Radioimmunotherapy for B-cell non-Hodgkin lymphoma

Best Practice & Research Clinical Haematology Vol. 19, No. 4, pp. 655e668, 2006 doi:10.1016/j.beha.2006.05.002 available online at http://www.sciencedirect.com

2 Radioimmunotherapy for B-cell non-Hodgkin lymphoma Thomas E. Witzig*

MD

Professor of Medicine Division of Hematology, Department of Internal Medicine, Mayo Clinic and Mayo Foundation, Stabile 6, 200 SW First Street, Rochester, MN 55905, USA

Radioimmunotherapy (RIT) combines the targeting advantage of a monoclonal antibody with the radiosensitivity of non-Hodgkin lymphoma (NHL) cells. There are now two radioimmunoconjugates (RICs) e ibritumomab tiuxetan (Zevalin
) and tositumomab (Bexxar
) e that are approved by the FDA in the US for relapsed low-grade or follicular B-cell NHL. Both agents target the CD20 antigen on B-cell lymphoma cells. In relapsed disease, single doses of RIT produce an 80% overall response rate, with approximately 20% of patients achieving durable responses. RIT is very well tolerated and is delivered on an outpatient basis over 1 week. The only significant toxicity is reversible myelosuppression. Both RIT agents have demonstrated high anti-tumor activity in patients who are refractory to rituximab. Current trials are testing RIT as initial therapy with rituximab maintenance, as adjuvant therapy after chemotherapy, or in high-dose protocols with stem-cell support. Key words: radioimmunotherapy; NHL; ibritumomab tiuxetan (Zevalin
); tositumomab (Bexxar
); CD20; radioimmunoconjugate.

The addition of the anti-CD20 monoclonal antibody rituximab to the therapeutic armamentarium has been one of the most important developments in the treatment of NHL in the last 25 years. Rituximab was the first monoclonal antibody to be approved by the FDA for the treatment of non-Hodgkin lymphoma (NHL), based on its single-agent activity in relapsed B-cell NHL.1 Rituximab immunotherapy is now routinely used in the treatment of low-grade NHL as an up-front single agent2,3 or as part of combination chemotherapy.4e6 The addition of rituximab to CHOP (cyclophosphamide, doxorubicin, vincristine, prednisone chemotherapy) has added approximately 15% to the overall survival (OS) for large-cell NHL.7e9 The unlabeled antibodies have indeed added efficacy, but many patients still relapse. One method of enhancing the cytotoxic potential of monoclonal antibodies is to * Tel.: þ1 507 266 9276; Fax: þ1 507 266 9277. E-mail address: [email protected]. 1521-6926/$ - see front matter ª 2006 Elsevier Ltd. All rights reserved.

656 T. E. Witzig

attach them to a radionuclide to form a radioimmunoconjugate (RIC). The use of an RIC is referred as to radioimmunotherapy (RIT) and has the advantage of targeting not only the cell to which the antibody is bound but also the surrounding tumor cells and microenvironment. The RIC kills tumor cells by the direct effects of the antibody e such as antibody-dependent cellular cytotoxicity (ADCC) e as well as by the effects of the ionizing radiation. There is also evidence that antibody bound to CD20 can enhance the pro-apoptotic effects of radiation.10 This review will focus on RIT that targets CD20, since it is now in clinical use for FDA-approved indications.11,12 Rituximab immunotherapy and anti-CD20 radioimmunotherapy have substantially improved the treatment options for patients with B-cell NHL, and have enhanced the survival not only of patients with large-cell NHL but also of those with follicular NHL.13 ANTI-CD20 RADIOLABELED ANTIBODIES Currently, there are two RICs registered in the US: ibritumomab tiuxetan (Zevalin
, BiogenIDEC) and tositumomab (Bexxar
, GlaxoSmithKline). Ibritumomab, a murine anti-CD20 antibody, was attached to tiuxetan, a MX-DTPA linkerechelator, to form ibritumomab tiuxetan. Tiuxetan forms a covalent, urea-type bond with ibritumomab and chelates the radionuclide via five carboxyl groups. Ibritumomab tiuxetan is then coupled with either indium-111 (111In) for tumor imaging and dosimetry, or with yttrium-90 (90Y) for therapy. 90Y emits pure b radioactivity with a path length of approximately 5 mm. Since there is no g emission, tumor and normal organ images cannot be obtained with 90 Y-ibritumomab tiuxetan. Therefore, g-emitting 111In-ibritumomab tiuxetan is used to produce images of the tumor and normal organs for dosimetry and biodistribution studies.14 The images are usually obtained between days 1 and 7 following 111In-ibritumomab tiuxetan injection to ensure that the 90Y-ibritumomab tiuxetan is targeting the tumor and that no unusual pattern of biodistribution to normal organs is occurring. The FDA currently requires one 111In-ibritumomab tiuxetan image 48 hours after injection (a second image is optional) for routine applications. This image is used to check for normal biodistribution and is not used to calculate the dose of 90Y-ibritumomab tiuxetan. Rather, the dose of 90Y-ibritumomab tiuxetan is determined by weight and baseline platelet count. The unlabeled antibody rituximab 250 mg/m2 is given before 90Y-ibritumomab tiuxetan to improve biodistribution.15 If there is normal biodistribution, on day 8 the patient receives another dose of rituximab followed by a therapeutic dose of 90Y-ibritumomab tiuxetan. If the platelet count is normal (>150,000 cells/mm3) the recommended dose is 0.4 mCi/kg; if the platelet count is 100,000e150,000 cells/mm3 the dose is 0.3 mCi/kg. The dose is capped at 32 mCi for patients weighing
80 kg. Tositumomab is a murine monoclonal antibody that binds to CD20. For RIT, tositumomab is radiolabeled with iodine-131 (131I). Since 131I emits g as well as b radiation, it can be used for both dosimetry and treatment.16 In contrast to 90Y-ibritumomab tiuxetan, the therapeutic dose of tositumomab is based on dosimetry.17 Patient-specific dosing is necessary because of the inter-patient differences in spleen size, tumor burden, and the metabolism and renal excretion of 131I.16e20 Iodine concentrate (Lugol’s solution) is given pre-treatment to block uptake of 131I in the thyroid. On day 1, 450 mg of cold tositumomab followed by 5 mCi of 131I-tositumomab is given. Dosimetry is performed on day 1 and repeated within 2e4 days and 6e7 days after the dose. Patients receive a dose of 131I-tositumomab calculated to deliver 75 cGy to the whole body for patients who have a platelet count >150,000 cells/mm3 or 65 cGy for patients with platelets between 100,000 and 150,000 cells/mm3. The therapeutic dose is given within 7e14 days of the

Radioimmunotherapy for B-cell NHL 657

dosimetric dose and consists of 450 mg of cold tositumomab followed by the calculated dose of 131I-tositumomab. PHASE I STUDIES OF ANTI-CD20 RADIOIMMUNOCONJUGATES The phase I studies had the goals of determining the dose of the cold antibody predose and the dose of the therapeutic RIC. These studies enrolled only patients with <25% marrow involvement, no evidence of marrow myelodysplasia, platelet count >100,000, and relatively normal renal and hepatic function. The phase I study of 90 Y-ibritumomab enrolled patients with relapsed low- or intermediate-grade CD20þ B-cell NHL.21 Comparison of images with 111In-ibritumomab tiuxetan performed with and without pre-dosing with unlabeled ibritumomab revealed that pre-dosing with cold antibodies improved biodistribution of 111In-ibritumomab tiuxetan. In the second phase I study, pre-dosing with rituximab rather than cold ibritumomab was tested, since rituximab (a humanized antibody, in contrast to murine ibritumomab) was less likely to induce the formation of human antimurine antibodies (HAMA) against ibritumomab tiuxetan. Fifty-one patients with low and intermediate grade or mantle cell lymphoma were enrolled. The study concluded that 250 mg/m2 of rituximab used before 111In-ibritumomab tiuxetan imaging and 90Y-ibritumomab tiuxetan therapy15 was acceptable for imaging and dosimetry. The doses of 90Y-ibritumomab tiuxetan used in the phase I/II trial were 0.2, 0.3, and 0.4 mCi/kg; higher doses were not tested in this trial because stem cells were not harvested pre-treatment and myelosuppression was the primary toxic effect. Across all dose levels tested the objective response rate (ORR) was 67%, with 26% complete remission (CR).15 In the phase I trial of 131I-tositumomab, the therapeutic dose was established as 75 cGy and pre-dosing with 450 mg of cold tositumomab was demonstrated to produce optimal tumor/normal organ biodistribution.18,22,23 The ORR was 71% (42/59) with 34% (20/59) CR in all histologic subtypes; the ORR was 83% in low-grade or transformed histology compared to 41% in patients with intermediate histology.23 TOXICITY OF ANTI-CD20 RADIOIMMUNOCONJUGATES The phase I trials clearly demonstrated that the primary toxic effect of RIT is myelosuppression. This myelosuppression becomes dose-limiting if stem-cell support is not available.24,25 The myelosuppression occurs late in comparison to that experienced with chemotherapy. The white blood cell (WBC) and platelet counts begin to drop at week 4 following the therapeutic dose of RIT, with the nadir occurring between weeks 6 and 9. By week 12 the counts have typically recovered. Patients who are on anticoagulants should be closely monitored during the period of thrombocytopenia to avoid hemorrhage. Patients with baseline platelet counts of 100,000e150,000 are recommended to receive 0.3 mCi/kg of 90Y-ibritumomab tiuxetan26 and a dose of 131 I-tositumomab calculated to deliver 65 cGy to the whole body.22,27 Interestingly, despite the neutropenia, serious infections are uncommon because RIT does not cause mucosal or skin toxicity; thus, barriers to microbes remain intact. Other toxic effects are usually mild. The incidence of human anti-mouse antibodies (HAMA) is <2% with ibritumomab tiuxetan and approximately 10% with tositumomab. The development of HAMA was higher in the trial of tositumomab for previously untreated patients.28 Development of myelodysplasia (MDS) and acute leukemia have been observed in patients treated with RIT; however, these patients had been treated with

658 T. E. Witzig

chemotherapy that included alkylating agents and/or purine nucleoside analogs prior to RIT.24,25,29,30 In the study of previously untreated patients who received RIT, no patient has developed MDS to date.28,30 Although longer follow-up is clearly necessary, it is reassuring that with over 10 years of experimental and clinical use RIT is not increasing the risk of MDS over chemotherapy alone. RADIOIMMUNOTHERAPY FOR PREVIOUSLY UNTREATED INDOLENT LYMPHOMA The majority of patients treated on clinical research trials and the patients treated subsequent to FDA approval have had relapsed or refractory low-grade follicular or transformed NHL. Only one published trial allowed previously untreated patients.28 This phase II trial treated 76 patients with previously untreated, advanced-stage (stage 3 or 4) follicular lymphoma (71% follicular grade 1 and 29% follicular grade 2) with a standard dose of 131I-tositumomab; 63% of the patients had bone-marrow involvement, 31% had an elevated lactate dehydrogenase (LDH), and 43% had bulky disease (masses
5 cm). The patients were relatively young, with a median age of 49 years (range: 23e69 years). The ORR was 95% (72/76) with a CR rate of 74% (56/76). Molecular CR was seen in 80% of assessable patients. After a median follow-up of 5.1 years, the 5-year progression-free survival PFS for all patients was 59%. As expected, the main toxicity was moderate myelosuppression, but no patient required a transfusion or growth factor use; 7% of the patients developed hypothyroidism and have subsequently required oral thyroid supplementation. Interestingly, 63% of patients developed a HAMA. This is a considerably higher percentage than observed in previously treated patients.18,27,29 The mechanism behind this difference is likely related to the blunted immune response observed in patients that have been heavily pretreated with chemotherapy. PATIENTS WITH RELAPSED AND REFRACTORY DISEASE Studies in relapsed and refractory follicular NHL were the first clinical efficacy studies performed using RIT. Several studies will be reviewed. Vose et al27 enrolled 47 patients with relapsed low-grade or transformed NHL. Patients received either 75 cGy or 65 cGy of 131I-tositumomab depending on baseline platelet count. The histology was low grade in 79% and transformed in 21%. The patients had previously received a median of four (range: one to eight) prior chemotherapy regimens, the LDH was elevated in 38%, and the bone marrow was involved in 51%. The ORR was 57%, and 32% of patients obtained a CR. The median response duration was 9.9 months. The achievement of CR was associated with a median duration of response (MDR) of 19.9 months. The median OS from study entry was 36 months; there were no treatment-related deaths. Although patients with indolent NHL can often respond to salvage regimens, the duration of the response typically shortens with each relapse.31 Kaminski et al performed a study to address the question of how the ORR to RIT with 131I-tositumomab compared to the response the patient had to their last chemotherapy prior to RIT.29 The study enrolled 60 patients with relapsed low-grade (n ¼ 36), transformed (n ¼ 23), or mantle-cell (n ¼ 1) NHL. The patients had received a median of four (range: 2 e 13) prior chemotherapy regimens and were required to have failed to respond or progressed within 6 months of the last chemotherapy regimen; 44% of the patients had an elevated LDH and 55% had bulky disease (mass
5 cm). The study clearly demonstrated that the ORR to RIT was 65% compared to 28% with

Radioimmunotherapy for B-cell NHL 659

chemotherapy (P < 0.001). The ORR was 81% in the low-grade patient group compared to 39% (9/29) in patients with transformed NHL. The MDR with 131I-tositumomab was 6.5 months compared to 3.4 months with chemotherapy; 17% had a CR with 131 I-tositumomab compared to 3% with chemotherapy (P ¼ 0.01).29 RADIOIMMUNOTHERAPY VERSUS IMMUNOTHERAPY The availability of rituximab in 1998 raised the question of whether the anti-CD20 RICs really offered any advantages over the respective unlabeled anti-CD20 antibodies. To address this important question, several studies were performed comparing the RIC with their respective cold counterparts. 90Y-ibritumomab tiuxetan was compared to rituximab in patients with relapsed CD20þ NHL who had never received rituximab. This study was launched before rituximab was widely available and prior to the studies of maintenance rituximab. Thus, it was possible to enroll rituximab-na€ıve patients and treat them with only four doses of standard rituximab. Patients with relapsed low-grade or follicular NHL were randomized to receive either 0.4 mCi/kg (maximum of 32 mCi) 90Y-ibritumomab tiuxetan or rituximab 375 mg/kg weekly  4;32 143 patients were randomized, 73 received 90Y-ibritumomab tiuxetan and 70 received rituximab. The ORR (International Workshop NHL criteria)33 was 80% with 90Yibritumomab tiuxetan compared to 56% for rituximab (P ¼ 0.002). The CR rate was 30% in the 90Y-ibritumomab tiuxetan group and 16% in the rituximab (P ¼ 0.04) group. The estimated median time to progression (TTP) was similar in both groups: 11.2 þ months (range: 0.8e31.5þ) for the 90Y-ibritumomab tiuxetan and 10.1 þ months (range: 0.7e26.1 months) for the rituximab group (P ¼ 0.173). However, the estimated time to next therapy for patients with non-transformed histology was significantly longer for 90Y-ibritumomab tiuxetan patients (17.8 þ months; range: 2.1e21.7þ) than for rituximab patients (11.2 months; range: 1.3e19.0þ) (P ¼ 0.040). The above study compared the human chimeric rituximab with its parent antibody (murine ibritumomab radiolabeled with 90Y). A somewhat similar study was done with 131 I-tositumomab; however, in this case the only difference was the radiolabel since both treatment arms used tositumomab.34 Seventy-eight patients with relapsed lowgrade and transformed NHL were randomized to receive 131I-tositumomab or two doses of cold tositumomab. The patients were a median age of 55 years (range: 28e85) and had received a median of two prior regimens (range: 1e5); 88% had stages III/IV, 40% had elevated LDH, and 41% had bulky disease (size
5 cm). The ORR was 55% for 131I-tositumomab compared to 19% for those who received cold tositumomab (P ¼ 0.002). The corresponding CR rates were 33% versus 8%, respectively. The MDR has not been reached for the 131I-tositumomab group versus 28.1 months for the cold tositumomab group. The MDR for the CR patients has not been reached for either treatment group. The median TTP was 6.3 months for the 131I-tositumomab versus 5.5 months (P ¼ 0.031); 27% of patients receiving 131I-tositumomab developed a HAMA. Nineteen patients who originally were randomized to tositumomab were crossed over to 131I-tositumomab and 68% responded. EFFICACY OF RADIOIMMUNOTHERAPY IN RITUXIMAB-REFRACTORY PATIENTS It soon became apparent that rituximab was being administered to most patients with NHL prior to consideration for RIT. The relevant question became: ‘will RIT work in

660 T. E. Witzig

patients who are resistant to rituximab?’ Two such studies have indeed demonstrated that the addition of the radioactive particle can overcome the resistance to the antiCD20 antibody alone. The first study evaluated the anti-tumor activity of 90Y-ibritumomab tiuxetan in 57 rituximab-refractory patients.35 In this study ‘rituximab-refractory’ was defined as no response to the patient’s last course of rituximab or a tumor response lasting <6 months. The median age was 54 years (range: 34e73), 95% of patients had follicular NHL, 32% had bone-marrow involvement, and 74% had bulky disease (
5 cm). This patient group had been heavily pretreated (median of four prior therapies). The ORR using International Workshop criteria33 was 74%, with 15% CR. The median estimated TTP was 6.8 months (range: 1.1e25.9þ) and 8.7 months (range: 1.7e25.9þ) for responders. In the second study reported by Horning et al,36 131I-tositumomab was administered to 40 patients who had relapsed after receiving rituximab. Thirty-five met the criteria of rituximab resistance; the other five patients had responded to rituximab for >6 months. The ORR was 65%, with 38% CR. The median progression-free survival was 10.4 months, and in responders it was 24.5 months. In summary, RIT for relapsed indolent NHL produces an ORR of approximately 60e80% and a complete response in 15e30% of patients. The RICs produce a higher response rate than their respective cold unlabeled antibody. RIT has a high response rate (approximately 75e80%) in rituximab-refractory patients. There have been several recent reports that have provided long-term follow-up results on the studies reviewed above. They suggest that approximately 20% of relapsed patients treated with a single dose of 131I-tositumomab or 90Y-ibritumomab tiuxetan have not yet relapsed. These patients tend to be those that achieved a CR.37e39 AGGRESSIVE OR TRANSFORMED NHL Patients with diffuse large-cell NHL that relapse after RCHOP and respond to salvage chemotherapy are typically treated with high-dose chemotherapy with stem-cell support. Therefore, the available experience of RIT in aggressive NHL is limited to relapsed refractory disease in patients who relapsed after e or were not eligible for e stem-cell transplantation. In the initial phase I/II of 90Y-ibritumomab tiuxetan the ORR was 43% for the 14 patients with intermediate-grade histology.15 A recent update on the long-term course of patients in that study demonstrated a 58% (7/12) ORR for the patients with diffuse large-cell histology with an MDR of 49.8 months (1.3e67.6þ).39 A more recent study with shorter follow-up evaluated 90Y-ibritumomab tiuxetan in the treatment of 104 elderly patients with relapsed and primary refractory diffuse large B-cell lymphoma that were not candidates for stem-cell transplantation. The ORR in the entire group was 44%.40 Patients not treated with rituximab-based chemotherapy had a 52% ORR compared with a 19% ORR in the group that had previously been treated with rituximab. The latter group appears to have been particularly highrisk since 37% were reported to be refractory to RCHOP. Although the treatment was generally well tolerated, four patients died due to adverse events. Three of these were cerebral hemorrhages associated with grade 4 thrombocytopenia; the other case was a late hemorrhage not attributed to RIT. The data on RIT in transformed NHL is derived from patients who were not candidates for high-dose chemotherapy and stem-cell transplantation. The experience with 71 patients with transformed NHL treated with 131I-tositumomab in five studies

Radioimmunotherapy for B-cell NHL 661

since 1990 has been reported.41 The median age was 59 years; median number of prior therapies was four (range: 1e11), 28% of the patients had bone-marrow involvement, 70% had bulky disease (>5 cm), 57% had elevated LDH, and 52% had an international prognostic index (IPI) score of 3 or more. The median follow-up was 19.4 months (range: 0.5e101). The ORR was 39%, with 25% CR. The MDR was 20 months (lower limit 10.8, upper limit not reached). The median TTP for all patients was 4.3 months (3.2e10.2), but for those who responded to the treatment the median TTP was 20.2 months (lower limit 12.4, upper limit not reached). Five patients remain in remission beyond 40 months. In summary, the use of RIT in the relapsed large-cell NHL patient is feasible and can produce gratifying responses in selected patients. Patients with low-bulk disease that is not progressing rapidly are ideal candidates for this treatment. MANTLE-CELL LYMPHOMA There have been limited trials of single-agent RIT for relapsed mantle-cell lymphoma (MCL). In the phase I/II trial of 90Y-ibritumomab tiuxetan there were three patients with MCL and none responded.15 A dedicated trial of 90Y-ibritumomab tiuxetan in 15 patients with relapsed MCL showed a 33% ORR with an MDR of 5.7 months.42 CHEMOTHERAPY AND STEM-CELL COLLECTION FOLLOWING RIT The myelosuppression universally observed after RIT has raised the question of the feasibility of chemotherapy following RIT. Ansell et al43,44 examined the subsequent therapy administered to 58 patients who had relapsed after receiving 0.4 mCi/kg of 90 Y-ibritumomab tiuxetan. The administered regimens were: 93% CHOP, 60% cyclophosphamide, vincristine and prednisone (CVP), 41% rituximab, 34% chlorambucil, 19% fludarabine, 14% ProMACE/CytoBOM, and 22% (13/58) received miscellaneous other regimens. Twenty-eight (48%) of the patients had transformed NHL (14 had the transformation before 90Y-ibritumomab tiuxetan, and in 14 the transformation developed after 90Y-ibritumomab tiuxetan). Subsequent chemotherapy was feasible and tolerable. Twenty-eight per cent of the patients received growth factors with their next chemotherapy, and two patients required reduced doses due to persistent myelosuppression. Peripheral blood stem-cell collection was also feasible, with one of eight patients requiring bone marrow harvest after failing peripheral blood stem-cell collection. All eight patients engrafted. Although these data are encouraging, if the patient is considered to be a candidate for autologous transplant, stem cells should be collected before RIT whenever possible. A single case report describes a successful autologous transplant following relapse after 131I-tositumomab.45 This issue has recently been addressed using the 131I-tositumomab patient database. Sixty-eight patients who relapsed a median of 168 days after RIT were reviewed.46 At the time of relapse, the median WBC was 4.9 K cells/mL (range: 1.1e21.4 K cells/mL) and the median platelet count was 130 K cells/mL (range: 9e440 K cells/mL); only the platelet count was significantly lower than the pre-RIT value. The 65% of patients (44/ 68) who received further chemotherapy were able to receive a median of two (range: one to four) additional regimens using typical myelosuppressive agents. Thirteen patients went on to stem-cell transplantation: three had stem cells harvested prior to RIT, ten after RIT.

662 T. E. Witzig

RE-TREATMENT WITH RADIOIMMUNOTHERAPY The data on re-treatment with RIT is limited to one fully published study47 and one reported only in abstract form.48 Thirty-two patients with a previous response to 131 I-tositumomab were eligible for re-treatment at the time of relapse. The patients had received a median of four therapies between the doses of 131I-tositumomab. The ORR to the second dose was 56% (18/32) with an MDR of 15.2 months. Eight patients (25%) had a CR and their MDR was 35 months, with five patients in a continued response 1.8e5.7 years on from the second dose. In ten of the 18 responders the response to the second treatment was longer than that experienced with the first dose of RIT. The rates of grade 3/4 neutropenia and thrombocytopenia were 50% and 43%, respectively; 10% of patients receiving the second dose developed a HAMA, and 12% developed an elevated serum thyroid-stimulating hormone level. Second malignancies occurred in six patients, and four developed MDS. There have been no reported studies of using a second dose of 90Y-ibritumomab tiuxetan at the time of relapse; however, there is an ongoing trial of two sequential doses of 90Y-ibritumomab tiuxetan. Patients in this trial have stem cells harvested and cryopreserved prior to receiving a single dose of 0.4 mCi/kg (maximum 32 mCi) of 90Y-ibritumomab tiuxetan. Patients responding with a CR or PR receive a second dose (the phase I dose) of 0.2, 0.3, or 0.4 mCi/kg of 90Y-ibritumomab tiuxetan.49 The trial is ongoing at the 0.4 mCi/kg cohort, and no patient has yet required stem-cell reinfusion (Dr G. Wiseman, personal communication March 27, 2006). It appears clear that both agents can be safely administered a second time. The determination of whether it is more efficacious to provide two sequential doses or one dose followed by the second course at relapse will require a randomized trial. COMBINATIONS OF RADIOIMMUNOTHERAPY AND CHEMOTHERAPY There have been limited studies of RIT combined with chemotherapy. Advanced follicular lymphoma is incurable with conventional chemotherapy and radiotherapy. The Southwest Oncology Group (SWOG) conducted a phase 2 trial (S9911) of CHOP  6 followed by a single dose of 131I-tositumomab. Ninety patients with previously untreated, advanced-stage follicular lymphoma were enrolled. The ORR was 90% with 67% CR/CRu’s. Forty-seven patients had less than a CR after CHOP. When these patients were restaged after 131I-tositumomab, 27 (57%) had improved their response to a CR. The 2-year PFS was estimated to be 81%, with a 2-year overall survival of 97%. The authors are currently conducting a trial that randomizes patients to either RCHOP or CHOP/131I-tositumomab. This trial e plus a large European trial that randomized patients after induction chemotherapy to observation (standard of care) versus a single dose of 90Y-ibritumomab tiuxetan e should provide important information of the ability of RIT to prolong TTP and OS compared to chemotherapy alone. The purine nucleoside analogues have also been tested in combination with RIT. Leonard et al50 treated 35 patients with three cycles of fludarabine (25 mg/m2/d  5 d q 5 weeks  3 cycles) followed by a single dose of 131I-tositumomab. The ORR to the combined therapy was 100%, with 86% of patients achieving a CR. The median PFS has yet to be reached and will be at least 48 months. Myelosuppression was the main toxicity, with grade 4 neutropenia and thrombocytopenia occurring in 16 (45%)

Radioimmunotherapy for B-cell NHL 663

and nine (26%) patients, respectively. Ten (25%) of patients received growth factor support and seven (20%) received blood product support. Only two patients required platelet transfusions after RIT. Two patients (6%) developed HAMA at days 184 and 195 from RIT. One patient has developed MDS. The Eastern Cooperative Oncology Group recently completed enrollment of patients with new, untreated mantle-cell NHL to a trial that administered RCHOP followed by a single course of 90Y-ibritumomab tiuxetan. There were no safety issues with the sequence of chemotherapy followed by RIT. Other trials in the cooperative groups are testing combinations of chemotherapy and RIT for newly diagnosed, earlystage diffuse large cell. RADIOIMMUNOTHERAPY WITH STEM-CELL SUPPORT It is clear that the primary dose-limiting toxicity of RIT for NHL is myelosuppression. One method of overcoming this limitation is to harvest stem cells prior to RIT and then re-infuse the stem cells after the radiation emitted from the RIT has decayed. In a phase I study, Press et al51 entered 43 patients, and 19 were able to receive therapeutic infusions of 131I-tositumomab. The ORR was 95% (18/19) and 84% (16/19) had a CR. An additional 25 patients were enrolled into the phase II trial52 and 84% (21/25) were treated. Tumor response was observed in 86% (18/21) with 76% CR. The stem cells were infused 12e18 days after 131I-tositumomab; the source of stem cells was bone marrow in 19 and blood stem cells in the other two. Neutrophil recovery to >500 and platelet count recovery to >20,000 occurred a median of 23 days and 22 days, respectively, after stem-cell infusion. HAMA was documented in 16%. Longterm follow-up (median 42 months) on these patients and those from the phase 1 trial demonstrated that the projected OS and PFS was 68% and 42%, respectively.53 These studies have been expanded to combine 131I-tositumomab with cyclophosphamide and etoposide with autologous stem-cell support;54 52 of the 55 enrolled received treatment. The median age was 47 years (range: 34e58). All patients were required to have a bone marrow that had <25% involvement with NHL. The study determined that a dose of 131I-tositumomab that delivered 25 Gy to critical normal organs could be safely combined with chemotherapy and stem cells. The estimated OS and PFS at 2 years were 83% and 68%, respectively. Sixteen patients with mantle-cell NHL have been treated with a similar protocol,55 and all patients had a tumor response with 91% CR. The OS and PFS at 3 years were 93 and 61%, respectively. Nademanee et al56 have published the first phase I/II trial of high-dose 90Y-ibritumomab tiuxetan combined with chemotherapy and autologous stem-cell support for patients with relapsed NHL. The patients received a dose of 90Y-ibritumomab tiuxetan calculated to deliver 1000 cGy to the highest normal organ followed by etoposide 40e60 mg/kg on day e4 and cyclophosphamide 100 mg/kg day e2. Thirty-one patients were treated. Histology included follicular lymphoma (n ¼ 12), diffuse large B cell (n ¼ 14), and mantle cell (n ¼ 5). The median dose of 90Y-ibritumomab tiuxetan calculated to deliver 1000 cGy to the highest normal organ was 71.6 mCi (2649.2 MBq; range: 36.6e105 mCi; range: 1354.2e3885 MBq). Engraftment was prompt, and the median times to reach an absolute neutrophil count (ANC) >500/mL and platelet count >20,000/mL were 10 days and 12 days, respectively. During follow-up there have been two deaths, and five patients have relapsed. The 2-year estimated OS is 92%, and the PFS is 78%. It is to be noted that in this trial the dose of 90Y-ibritumomab

664 T. E. Witzig

tiuxetan was not dose-escalated beyond a dose calculated to deliver 1000 cGy to the liver. Another trial e combining 90Y-ibritumomab tiuxetan with BEAM conditioning chemotherapy and stem cells e is dose-escalating the 90Y-ibritumomab tiuxetan in a typical phase I protocol. That trial has been published in abstract form57,58 and continues to accrue patients. The current dose is 1700 cGy to the liver (Jane Winter, MD, personal communication March 2006). RADIATION THERAPY AFTER RADIOIMMUNOTHERAPY A recent report has demonstrated that patients who relapse or progress with RIT can respond to external beam radiation. Justice et al59 reviewed 19 patients who received radiation therapy after 90Y-ibritumomab tiuxetan. They found a 90% (26/29 sites radiated) ORR, with 12 (41%) CR, seven (24%) CCR, seven (24%) PR, and three (10%) stable. Toxicities were generally transient, reversible, and corresponded to the anatomic regions irradiated. CURRENT RECOMMENDATIONS RIT with either 90Y-ibritumomab tiuxetan or 131I-tositumomab is a very attractive option for patients who have relapsed after chemotherapy. The advantages of RIT are that it has a high ORR with a single dose delivered on an outpatient basis. The RIT agents have few immediate side-effects, a low risk of nausea or vomiting, no alopecia, and a low risk of toxicity to normal organs other than the bone marrow. They are ideal for disease in locations such as the orbit or parotid where external beam radiotherapy can produce long-term side-effects. A disadvantage of RIT is that it cannot be used in patients with poor marrow reserve or heavy marrow involvement with NHL. Patients with very bulky disease (>10 cm) are not good candidates for RIT alone. These patients should receive debulking chemotherapy prior to RIT for optimal response. There is also a paucity of data on small lymphocytic lymphoma/chronic lymphocytic leukemia since these patients usually have >5000 absolute lymphocytes in the blood, making them ineligible for RIT. FUTURE DIRECTIONS Many of the current clinical trials for NHL are focusing on testing RIT as adjuvant therapy after rituximab-based chemotherapy or in higher doses with chemotherapy and stem-cell support. Other approaches being tested are RIT with radiosensitizers such as bortezomib or immunostimulatory agents such as cytidine-phosphate-guanosine (CpG). The results of these trials should be available in the next few years and will be important in defining the role of RIT in the overall treatment program for patients with NHL. SUMMARY RIT with either 90Y-ibritumomab tiuxetan or 131I-tositumomab is highly effective and safe for the treatment of relapsed low-grade or follicular NHL, irrespective of prior treatment with rituximab. RIT also induces high response rates in patients with newly diagnosed follicular lymphoma. However, similar results in newly diagnosed patients can be achieved with other therapies, and the role of RIT e including optimal

Radioimmunotherapy for B-cell NHL 665

sequencing with chemotherapy e will have to be established in randomized studies. Similarly, the value of re-treatment with RIT, and RIT in aggressive NHL, requires further study.

Practice points  radioimmunotherapy is an effective, well-tolerated therapy for patients with relapsed low-grade or follicular NHL  patients should have a platelet count >100,000 and an absolute neutrophil count >1500  patients with myelodysplasia should not receive RIT  radioimmunotherapy is effective for patients with previously untreated NHL; only patients who achieve CR have durable responses

Research agenda  important studies evaluating high-dose radioimmunotherapy with chemotherapy and stem-cell support for relapsed NHL are ongoing. The results to date indicate a high overall response rate and better results than historical controls; however, randomized trials have not yet been initiated  radioimmunotherapy is being added as adjuvant therapy for patients with indolent and aggressive NHL who have completed chemotherapy to learn whether the time-to-progression and overall survival can be prolonged; the results of these randomized studies could change the standard of care for these malignancies  radiosensitizers are being added to radioimmunotherapy to find out whether they can enhance response and duration of response  rituximab maintenance is being tested after radioimmunotherapy to learn whether the duration of the response can be prolonged

ACKNOWLEDGEMENTS Supported in part by a Lymphoma SPORE grant CA97274 from the National Cancer Institute. REFERENCES 1. McLaughlin P, Grillo-Lopez AJ, Link BK et al. Rituximab chimeric anti-CD20 monoclonal antibody therapy for relapsed indolent lymphoma: half of patients respond to a four-dose treatment program. Journal of Clinical Oncology 1998; 16: 2825e2833. 2. Witzig TE, Vukov AM, Habermann TM et al. Rituximab therapy for patients with newly diagnosed, advanced-stage, follicular grade I non-Hodgkin’s lymphoma: a phase II trial in the North Central Cancer Treatment Group. Journal of Clinical Oncology 2005; 23: 1103e1108.

666 T. E. Witzig 3. Colombat P, Salles G, Brousse N et al. Rituximab (anti-CD20 monoclonal antibody) as single first-line therapy for patients with follicular lymphoma with a low tumor burden: clinical and molecular evaluation. Blood 2001; 97: 101e106. 4. Hochster HS, Weller E, Gascoyne R et al. Maintenance rituximab after CVP results in superior clinical outcome in advanced follicular lymphoma: results of the E1496 phase III trial from the Eastern Cooperative Oncology Group and the Cancer and Leukemia Group B. Blood 2005; 106(11): 349. 5. Marcus R, Imrie K, Belch A et al. CVP chemotherapy plus rituximab compared with CVP as first-line treatment for advanced follicular lymphoma. Blood 2005; 105: 1417e1423. 6. Van Oers MHJ, Glabbeke MV, Tzeodorovic I et al. Chimeric anti-CD20 monoclonal antibody (Rituximab;Mabthera) in remission induction and maintenance treatment of relapsed/resistant follicular non-Hodgkin’s lymphoma: final analysis of a phase III randomized intergroup clinical trial. Session Type: Oral Session. Blood 2005; 106 [Abstract 353]. 7. Mounier N, Briere J, Gisselbrecht C et al. Rituximab plus CHOP (R-CHOP) overcomes bcl-2eassociated resistance to chemotherapy in elderly patients with diffuse large B-cell lymphoma (DLBCL). Blood 2003; 101: 4279e4284. 8. Coiffier B, Lepage E, Briere J et al. CHOP chemotherapy plus rituximab compared with CHOP alone in elderly patients with diffuse large-B-cell lymphoma. The New England Journal of Medicine 2002; 346: 235e242. 9. Habermann TM, Weller EA, Morrison VA et al. Rituximab-CHOP vs CHOP alone or with maintenance rituximab in older patients with diffuse large B-cell lympoma. Journal of Clinical Oncology 2006; 24(19): 3121e3127. 10. Skvortsova I, Popper BA, Skvortsov S et al. Pretreatment with rituximab enhances radiosensitivity of non-Hodgkin’s lymphoma cells. Journal of Radiation Research 2005; 46: 241e248. 11. Dillman RO. Radiolabeled anti-CD20 monoclonal antibodies for the treatment of B-cell lymphoma. Journal of Clinical Oncology 2002; 20: 3545e3557. 12. Cheson BD. Radioimmunotherapy of non-Hodgkin lymphomas. Blood 2003; 101: 391e398. 13. Fisher RI, LeBlanc M, Press OW et al. New treatment options have changed the survival of patients with follicular lymphoma. Journal of Clinical Oncology 2005; 23: 8447e8452. *14. Wiseman GA, Kornmehl E, Leigh B et al. Radiation dosimetry results and safety correlations from 90Yibritumomab tiuxetan radioimmunotherapy for relapsed or refractory non-Hodgkin’s lymphoma: combined data from 4 clinical trials. Journal of Nuclear Medicine 2003; 44: 465e474. *15. Witzig TE, White CA, Wiseman GA et al. Phase I/II trial of IDEC-Y2B8 radioimmunotherapy for treatment of relapsed or refractory CD20(þ) B-cell non-Hodgkin’s lymphoma. Journal of Clinical Oncology 1999; 17: 3793e3803. 16. Wahl RL, Zasadny KR, MacFarlane D et al. Iodine-131 anti-B1 antibody for B-cell lymphoma: an update on the Michigan Phase I experience. Journal of Nuclear Medicine 1998; 39: 21Se27S. 17. Wahl RL, Kroll S & Zasadny KR. Patient-specific whole-body dosimetry: principles and a simplified method for clinical implementation. Journal of Nuclear Medicine 1998; 39: 14Se20S. 18. Kaminski MS, Zasadny KR, Francis IR et al. Radioimmunotherapy of B-cell lymphoma with [131I]anti-B1 (anti-CD20) antibody. The New England Journal of Medicine 1993; 329: 459e465. 19. Wahl RL. Iodine-131 anti-B1 antibody therapy in non-Hodgkin’s lymphoma: dosimetry and clinical implications. Journal of Nuclear Medicine 1998; 39: 1S. 20. Koral KF, Dewaraja Y, Li J et al. Update on hybrid conjugate-view SPECT tumor dosimetry and response in 131I-tositumomab therapy of previously untreated lymphoma patients. Journal of Nuclear Medicine 2003; 44: 457e464. 21. Knox SJ, Goris ML, Trisler K et al. Yttrium-90-labeled anti-CD20 monoclonal antibody therapy of recurrent B-cell lymphoma. Clinical Cancer Research 1996; 2: 457e470. 22. Kaminski MS, Zasadny KR, Francis IR et al. Iodine-131-anti-B1 radioimmunotherapy for B-cell lymphoma. Journal of Clinical Oncology 1996; 14: 1974e1981. 23. Stagg R, Wahl RL, Estes J et al. Phase I/II study of iodine-131 anti-B1 antibody for non-Hodgkin’s lymphoma (NHL): final results. Proceedings of the American Society of Clinical Oncology 1998; 17: 39a. [Abstract 150]. *24. Witzig TE, White CA, Gordon LI et al. Safety of yttrium-90 ibritumomab tiuxetan radioimmunotherapy for relapsed low-grade, follicular, or transformed non-hodgkin’s lymphoma. Journal of Clinical Oncology 2003; 21: 1263e1270.

Radioimmunotherapy for B-cell NHL 667 25. Fehrenbacher L, Radford JA, Kaminski M et al. Patient-specific dosing of Bexxar
is associated with tolerable and predictable hematologic toxicity in patients with known hematologic risk factors. Proceedings of the American Society of Clinical Oncology 2001; 20: 287a. [Abstract 1144]. 26. Wiseman GA, Gordon LI, Multani PS et al. Ibritumomab tiuxetan radioimmunotherapy for patients with relapsed or refractory non-Hodgkin lymphoma and mild thrombocytopenia: a phase II multicenter trial. Blood 2002; 99: 4336e4342. *27. Vose JM, Wahl RL, Saleh M et al. Multicenter phase II study of iodine-131 tositumomab for chemotherapy-relapsed/refractory low-grade and transformed low-grade B-cell non-Hodgkin’s lymphomas. Journal of Clinical Oncology 2000; 18: 1316e1323. *28. Kaminski MS, Tuck M, Estes J et al. 131I-tositumomab therapy as initial treatment for follicular lymphoma. The New England Journal of Medicine 2005; 352: 441e449. *29. Kaminski MS, Zelenetz AD, Press OW et al. Pivotal study of iodine I 131 tositumomab for chemotherapyrefractory low-grade or transformed low-grade B-cell non-Hodgkin’s lymphomas. Journal of Clinical Oncology 2001; 19: 3918e3928. *30. Bennett JM, Kaminski MS, Leonard JP et al. Assessment of treatment-related myelodysplastic syndromes and acute myeloid leukemia in patients with non-Hodgkin lymphoma treated with tositumomab and iodine I131 tositumomab. Blood 2005; 105: 4576e4582. 31. Gallagher CJ, Gregory WM, Jones AE et al. Follicular lymphoma: prognostic factors for response and survival. Journal of Clinical Oncology 1986; 4: 1470e1480. *32. Witzig TE, Gordon LI, Cabanillas F et al. Randomized controlled trial of 90Y-labeled ibritumomab tiuxetan (zevalin) radioimmunotherapy versus rituximab immunotherapy for patients with relapsed or refractory low-grade, follicular, or transformed b-cell non-Hodgkin’s lymphoma. Journal of Clinical Oncology 2002; 20: 2453e2463. 33. Cheson B, Horning S, Coiffier B et al. Report of an international workshop to standardize response criteria for non-Hodgkin’s lymphoma. Journal of Clinical Oncology 1999; 17: 1244e1253. 34. Davis TA, Kaminski MS, Leonard JP et al. The radioisotope contributes significantly to the activity of radioimmunotherapy. Clinical Cancer Research 2004; 10: 7792e7798. 35. Witzig TE, Flinn IW, Gordon LI et al. Treatment with ibritumomab tiuxetan radioimmunotherapy in patients with rituximab-refractory follicular non-Hodgkin’s lymphoma. Journal of Clinical Oncology 2002; 20: 3262e3269. 36. Horning SJ, Younes A, Jain V et al. Efficacy and safety of tositumomab and iodine-131 tositumomab (Bexxar) in B-cell lymphoma, progressive after rituximab. Journal of Clinical Oncology 2005; 23: 712e719. 37. Wiseman GA & Witzig TE. Yttrium-90 (90Y) ibritumomab tiuxetan (Zevalin) induces long-term durable responses in patients with relapsed or refractory B-Cell non-Hodgkin’s lymphoma. Cancer Biotherapy & Radiopharmaceuticals 2005; 20: 185e188. *38. Fisher RI, Kaminski MS, Wahl RL et al. Tositumomab and iodine-131 tositumomab produces durable complete remissions in a subset of heavily pretreated patients with low-grade and transformed nonHodgkin’s lymphomas. Journal of Clinical Oncology 2005; 23: 7565e7573. *39. Gordon LI, Molina A, Witzig Tet al. Durable responses after ibritumomab tiuxetan radioimmunotherapy for CD20þ B-cell lymphoma: long-term follow-up of a phase 1/2 study. Blood 2004; 103: 4429e4431. 40. Morschhauser F, Huglo D, Martinelli G et al. Yttrium-90 ibritumomab tiuxetan (Zevalin) for patients with relapsed/refractory diffuse large B-cell lymphoma not appropriate for autologous stem cell transplantation: results of an open-label phase II trial. Blood 2004; 110 [Abstract 130]. 41. Zelenetz A, Saleh M, Vose J et al. Patients with transformed low grade lymphoma attain durable responses following outpatient radioimmunotherapy with tositumomab and iodine I 131 tositumomab [Bexxar]. Blood 2002; 100 [Abstract]. 42. Oki Y, Pro B, Delpassand E et al. A phase II study of yttrium 90 (90Y) ibritumomab tiuxetan (Zevalin) for treatment of patients with relapsed and refractory mantle cell lymphoma (MCL). Blood 2004; 104: 2632. [Abstract]. 43. Ansell SM, Ristow KM, Habermann TM et al. Subsequent chemotherapy regimens are well tolerated after radioimmunotherapy with yttrium-90 ibritumomab tiuxetan for non-Hodgkin’s lymphoma. Journal of Clinical Oncology 2002; 20: 3885e3890. 44. Ansell SM, Schilder RJ, Pieslor PC et al. Antilymphoma treatments given subsequent to yttrium 90 ibritumomab tiuxetan are feasible in patients with progressive non-Hodgkin’s lymphoma: a review of the literature. Clinical Lymphoma 2004; 5: 202e204.

668 T. E. Witzig 45. Cooney J, Stiff P & Kaminski M. Successful autologous peripheral blood stem cell transplantation in transformed follicular lymphoma previously treated with radioimmunotherapy (iodine (131)I tositumomab). Bone Marrow Transplantation 2002; 29: 523e525. 46. Dosik AD, Coleman M, Kostakoglu L et al. Subsequent therapy can be administered after tositumomab and iodine I-131 tositumomab for non-Hodgkin lymphoma. Cancer 2006; 106: 616e622. 47. Kaminski MS, Radford JA, Gregory SA et al. Re-treatment with I-131 tositumomab in patients with non-Hodgkin’s lymphoma who had previously responded to I-131 tositumomab. Journal of Clinical Oncology 2005; 23: 7985e7993. 48. Wiseman G, Colgan J, Inwards D et al. Yttrium-90 Zevalin phase I sequential dose radioimmunotherapy trial of patients with relapsed low grade and follicular B-cell non-Hodgkins lymphoma (NHL): preliminary results. Blood 2002; 100: 358a. [Abstract 1387]. 49. Wiseman G & Witzig T. Yttrium-90 Zevalin phase I sequential dose radioimmunotherapy trial of patients with relapsed low grade and follicular B-cell non-Hodgkins lymphoma (NHL): preliminary results. Blood 2002; 100: 358a. [Abstract 1387]. 50. Leonard JP, Coleman M, Kostakoglu L et al. Abbreviated chemotherapy with fludarabine followed by tositumomab and iodine I 131 tositumomab for untreated follicular lymphoma. Journal of Clinical Oncology 2005; 23: 5696e5704. 51. Press OW, Eary JF, Appelbaum FR et al. Radiolabeled-antibody therapy of B-cell lymphoma with autologous bone marrow support [see comments]. The New England Journal of Medicine 1993; 329: 1219e1224. 52. Press OW, Eary JF, Appelbaum FR et al. Phase II trial of 131I-B1 (anti-CD20) antibody therapy with autologous stem cell transplantation for relapsed B cell lymphomas. Lancet 1995; 346: 336e340. 53. Liu SY, Eary JF, Petersdorf SH et al. Follow-up of relapsed B-cell lymphoma patients treated with iodine131-labeled anti-CD20 antibody and autologous stem-cell rescue. Journal of Clinical Oncology 1998; 16: 3270e3278. 54. Press O, Eary J, Gooley T et al. A phase I/II trial of iodine-131-tositumomab (anti-CD20), etoposide, cyclophosphamide, and autologous stem cell transplantation for relapsed B-cell lymphomas. Blood 2000; 96: 2934e2942. 55. Gopal AK, Rajendran JG, Petersdorf SH et al. High-dose chemo-radioimmunotherapy with autologous stem cell support for relapsed mantle cell lymphoma. Blood 2002; 99: 3158e3162. 56. Nademanee A, Forman S, Molina A et al. A phase 1/2 trial of high-dose yttrium-90-ibritumomab tiuxetan in combination with high-dose etoposide and cyclophosphamide followed by autologous stem cell transplantation in patients with poor-risk or relapsed non-Hodgkin lymphoma. Blood 2005; 106: 2896e2902. 57. Winter JN. Combining yttrium 90-labeled ibritumomab tiuxetan with high-dose chemotherapy and stem cell support in patients with relapsed non-Hodgkin’s lymphoma. Clincal Lymphoma 2004; 5: S22eS26. 58. Winter JN, Inwards D, Erwin W et al. Zevalin dose-escalation followed by high-dose BEAM and autologous peripheral blood progenitor cell (PBPC) transplant in non-Hodgkin’s lymphoma: early outcome results. Blood 2002; 100: 411a. [Abstract 1597]. 59. Justice T, Martenson Jr. JA, Wiseman G et al. Safety and efficacy of external beam radiation therapy for non-Hodgkin lymphoma in patients with prior 90Y-ibritumomab tiuxetan radioimmunotherapy. Cancer 2006; 107(2): 433e438.