Clinical comparison of radiolocalization of two monoclonal antibodies (mAbs) against the TAG-72 antigen

Nucl. Med. Biol. Vol. 21, No. I, pp.9-15, 1994 Printed in Great Britain. All rights reserved

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0969-805 l/94 $6.00 + 0.00 80 1994 Pergamon Press Ltd

Clinical Comparison of Radiolocalization Two Monoclonal Antibodies (mAbs) Against the TAG-72 Antigen

of

C. R. DIVGI’*, A. M. SCOTT’, K. MCDERMOTT’, P. S. FALLONE’, S. HILTON’, K. SILER’, N. CARMICHAEL’, F. DAGHIGHIAN’, R. D. FINN’, A. M. COHEN’, J. SCHLOM’ and S. M. LARSON’ ‘Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10021 and rNational Cancer Institute, Bethesda, MD 20892, U.S.A. (Accepted I August 1993) Ten patients with colorectal cancer metastases received 12jI-B72.3 and “‘ICC49 prior to laparotomy (five patients received 1 mg, and five 20 mg of each mAb). Tumor: serum ratios of ‘j’ I-CC49 were better than those of ‘251-B72.3 (P < 0.01 at I mg; P = 0.05 at 20 mg; P < 0.01 at both doses). All known lesions > 1 cm in diameter were visualized at the 20 mg dose. There was no difference in absolute tumor uptake of ‘*51LB72.3or i3’ICC49. We conclude that mAb CC49 has better relative uptake in colorectal cancers than mAb B72.3.

Introduction

biological dose (OBD); if the OBD is not known, then an appropriate dose escalation needs to be incorporated into the trial design. The mAbs must not compete for the same antigenic epitope; they must both be labeled in identical fashion with the same element. The same element must be used because there are considerable differences between radiometal- and radioiodine-labeled antibodies, among them differences in hepatic uptake and in vivo detachment of radiolabel from antibody. The major advantage of studying two mAbs against a given cancer system in the same patient or patient group is that the mAbs can then be directly compared to each other in the same tissue sampling, reducing a number of potential sources of variation between specimens, such as variations in antigen expression, the fraction of specimen which is tumor, variations in extracellular volume and non-specific or passive accumulation of radioantibody etc., reducing the number of samples required for statistical significance. With the ultimate aim of choosing an appropriate mAb for radioimmunotherapy of colorectal cancer, we compared I25I-B72.3 and 13’ILCC49, two murine IgG, mAbs reacting against different epitopes on the same antigen, TAG-72, in pre-surgical patients with metastatic colorectal cancer.

Monoclonal antibodies (mAbs) against several antigenic systems in colorectal cancer have been studied (Goldenberg et al., 1978; Mach et al., 1983; Beatty et af., 1986; Patt et al., 1988; Abdel-Nabi et al., 1988, 1990; Bischof-Delaloye et al., 1989; Corbisiero et al., 1991; Griffin et al., 1991; Divgi et a!., 1991; Esteban et al., 1987; Colcher et al., 1987; Carrasquillo et al., 1988; Welt et al., 1991). Two secreted antigens, carcinoembryonic antigen (CEA) and tumor associated glycoprotein-72 (TAG-72) have received the most attention (Goldenberg et al., 1978; Mach et al., 1983; Beatty et al., 1986; Patt et al., 1988; Abdel-Nabi et al., 1988, 1990; Bischof-Delaloye et al., 1989; Corbisiero et al., 1991; Griffin et al., 1991; Divgi et al., 1991; Esteban et al., 1987; Colcher et al., 1987; Carrasquillo et al., 1988). There is a need for clinical trials comparing two or more antibodies against the same antigen in the same patient population so that appropriate evaluation of these antibodies may be made to select the better antibody for further development, either for radioimmunodetection or for radioimmunotherapy. There are several important points to consider in the appropriate design of clinical trials comparing mAbs against a given antigen. It is important that the mAbs to be compared are used at their optimum

Materials and Methods Patients

*All correspondence should be addressed to: Chaitanya T. Divgi, Nuclear Medicine Service, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, NY 10021, U.S.A.

Ten patients with metastatic colorectal carcinoma who were candidates for exploratory laparotomy for 9

C. R. DIVGIez al.

10

resection of metastatic disease and/or placement of a hepatic intra-arterial infusion pump, were studied. Requirements included a negative human anti-mouse antibody serum titer and adequate renal, hepatic and hematopoietic function. The radioimmunolocalization study was approved by the Institution Review Board at this center. Informed consent was obtained from all patients. Patients l-8 had hepatic metastases at the time of presentation; patient 9 had a right adrenal metastasis and patient 10 had a pelvic recurrence. All patients underwent standard imaging modalities including abdominal CT scans, and subsequently underwent biopsy of suspected lesion(s). The first five patients received 1 mg each of lZSI-B72.3 and i3’I-CC49 labeled with <74 MBq (2 mCi) “‘1 and < 370 MBq (10 mCi) 13’I, respectively. The second group of 5 patients received 20 mg each of B72.3 and CC49 labeled with similar amounts of radioiodine. Patient characteristics are summarized in Table 1. Monoclonal antibodies

Both murine IgG, monoclonal antibodies were developed in the laboratory of Jeffrey Schlom at the National Cancer Institute. MAb B72.3 is a murine IgG, that reacts against TAG-72, a secreted antigen found in most mutinous adenocarcinomas (Johnson et al., 1986). MAb CC49 is a higher affinity “second generation” murine IgG, that reacts with a different epitope on the same antigen (Kuroki et al., 1990). The K, for B72.3 is 2.5 x lo9 M-l, while that for CC49 is about 8-fold greater. B72.3 was labeled with I25I and CC49 with “‘I using the Iodogen (Pierce Inc., Rockford, Ill.) method. Briefly: the requisite amount of mAb and radioiodine were mixed in sterile 10 mL glass vials precoated with Iodogen and incubated at room temperature for 15 min. The radiolabeled mAb

Table 1. Characteristics

was separated from the mixture by passage through a BioGel P6 (Bio-Rad Inc., Melville, N.Y.) size exclusion column. Thin layer chromatography of an aliquot was carried out and the preparation utilized only if the percent of protein-bound radioactivity was 295%. Radioimmunoreactivity

Every injected dose of each radiolabeled mAb was assayed for radioimmunoreactivity using the method described by Lindmo et al. (1984). Briefly: appropriate dilutions of each mAb were added in triplicate to wells of microtiter plates precoated with antigenpositive (LS174T) and antigen-negative (A435) cell extract and incubated at 4°C for 1 h. The percent of bound radioactivity was plotted against dilution to obtain the percent binding at conditions of antigen excess. Specific radioimmunoreactivity was calculated as the difference between the percent bound to the antigen-positive wells and that bound to the antigennegative wells. Administration of radiolabeled mAbs

Patients received the radiolabeled mAbs a week prior to surgery. Both radiolabeled mAbs were diluted in 100 mL 5% HSA in normal saline and administered as an intravenous infusion over 1 h. Patients were monitored for vital signs for at least 4 h after completion of antibody infusion. Pharmacokinetics and radioimmunoscintigraphy

Blood was obtained for determination of radiolabeled mAb clearance immediately following antibody infusion; after 60 min, and subsequently at least at each imaging time point as well as on the day of surgery.

of the 10 patients studied, including the serum half-life of each radioiodinated (sCEA = serum CEA, in ng/mL) Lesions detected

Dose

Patient No.

Sex

Aee

sCEA

1“x

I

F

47

94

2

M

52

159

3

F

67

228

4

M

54

27

5

F

71

5

6

M

54

12

7

M

66

5

8*

M

61

27

9

M

43

10

M

49

20 mg

mAb

Serum T,,, (h)

CT scan (diameter)

MAB scan

cc49

Negative

50.96

69.3

Hepatic

43.3

49.5

Negative

43.3

37.1

Negative

49.5

59.2

Hepatic

43.3

49.5

Hepatic

46. I

52. I

Hepatic

51.5

58.4

Hepatic

41.3

51.4

37

Hepatic (R) lobe: (1.5 cm) (L) lobe: (2 cm) Hepatic (R) lobe: (3 cm) Hepatic (R) lobe: (2 cm) Hepatic (R) lobe: (5 cm) Hepatic (R) lobe: (4 cm) Hepatic (R) lobe: (3 cm) Hepatic (R) lobe: (4cm) Hepatic (R) lobe: (2 cm) (R) Adrenal (4 cm)

52.1

53.1

76

Pelvic (6 . cm),

(R) Adrenal, hepatict Pelvic

69.8

72.3

*Patient 8 had additional para-aortic nodal disease seen only on laparotomy. tLeft lobe lesion seen on CT scan 7 months later, confirmed then at laparotomy.

B72.3

Comparison of anti-TAG-72 mAbs in colon cancer Anterior and posterior whole body 13’1 images were obtained on the day of infusion as well as at two time points (the first usually 2-3 days after infusion, and the second usually 4-5 days after infusion) prior to surgery. Additional anterior and posterior spot images of the thorax, abdomen and pelvis were obtained, as was at least one single photon computed tomograph (SPECT) of the abdomen, obtained between 2 and 4 days after antibody infusion. SPECT images were studied in the transverse, coronal and sagittal planes. In vitro studies Samples of serum (0.5 mL each) were counted in a y-counter along with appropriate dilutions of the standards and biopsy specimens. All serum, tissue and standard counts were obtained at the same time. Samples were simultaneously counted in the “‘1 and 13’1windows in a y-well scintillation counter (LKB Wallac, Piscataway, N.J.). Absolute “‘1 was calculated after suitable adjustments for down-scatter from the 13’I. Samples were counted to less than 1% relative error, according to the criteria of Loevinger and Berman (1951).

Results Ten patients with known colorectal carcinoma with evidence of metastatic disease were studied (Table 1). Eight patients had known hepatic disease prior to surgery; in one of them, para-aortic nodal involvement was noted at surgery. One patient had a right adrenal lesion, while patient 10 had a pelvic recurrence. The labeling method was simple and efficient. The procedure reproducibly resulted in 290% incorporation of radioiodine to antibody as determined by thin layer chromatography. Specific radioirnmunoreactivity of lz51-B72.3 was > 35%; that of ‘3’IICC49 >55%. None of the patients had any side effects during or after antibody infusion. Imaging

All radioimmunoscintigraphic scans (MAB scans) were initially interpreted without knowledge of the other imaging findings. Radionuclide scans were interpreted as positive if there were focal areas of increased tracer concentration in the liver. Nodal areas of increased radiotracer concentration were interpreted as positive only if the uptake was persistent. SPECT delineated lesion extent better than did the planar images. Whole body 13’I-CC49 imaging carried out on the day of infusion showed blood pool images; this corresponded with pharmacokinetic analysis which demonstrated initial radioactivity confined to the vascular compartment (between 14 and 32% of the injected dose per liter of serum). Lesions were usually visualized by day 2 or 3, with improved tumor contrast at later time points. SPECT especially improved delineation of hepatic lesions. Two of five

II

patients at the 1 mg dose and all five patients at the 20mg dose had positive visualization of known hepatic lesions. At the 20 mg dose, all known lesions in 5 patients were visualized. In one patient at this dose level, para-aortic nodal disease < 1 cm in diameter, not visualized on the CT scan, was also not visualized on MAB scans. The small number of patients studied precluded adequate evaluation of the sensitivity and specificity of radioimmunoscintigraphy with ‘3’I-CC49 in the detection of metastatic colorectal cancer. Two clinical cases are presented. The first is patient 5, a 71-year-old female with colon carcinoma who presented with a serum CEA of 5 ng/mL and a CT scan showing a solitary 4cm diameter right hepatic lobe lesion [Fig. l(a)], who received 1 mg each of ‘251-B72.3 and i3’I-CC49. MAB scans [Fig. l(b)] showed uptake in the known right lobe lesion with no other focus of abnormal radionuclide concentration. At surgery, the only disease found was the known right hepatic lesion. Patient 9 was a 43-year-old male with a history of colon carcinoma who presented with a 3 cm right adrenal lesion seen on the CT scan (Fig. 2, lower left panel). The patient received 20 mg each of ‘251-B72.3 and 13’ICC49. MAB scans showed uptake of 13’I in the known adrenal mass (Fig. 2, upper left panel). In addition, another area of abnormal uptake was seen in the left hepatic lobe (Fig. 2, upper right panel). Figure 2, lower right panel, shows the corresponding, normal, CT scan. A posterior approach was used for resection of the adrenal mass, precluding adequate exploration of the left lobe of the liver. The right adrenal mass was resected and confirmed to be metastatic colon carcinoma. The left hepatic lobe lesion was visualized on CT 6 months following right adrenal resection, and confirmed upon subsequent laparotomy to be metastatic colon carcinoma. Pharmacokinetics and radiolocalization

Both mAbs showed a monoexponential clearance of blood radioactivity. The mean serum T,,, was 49.12 h (range 41.3-69.8 h) for ‘3’I-CC49 and 55.25 h (range 37.1-72.3 h) for 1251-B72.3 (P = NS) (Table 1). There was no correlation between blood T,12and injected dose in the patients. Table 2 shows the mean percent injected dose per gram of tumor in the various biopsy specimens as well as the tumor: serum ratios for each mAb. Multiple portions of the same tumor were sampled in order to obtain an idea of the heterogeneity of radioantibody distribution. There was a wide range of mAb tumor uptake even within the same tumor (Table 2). Comparison of absolute tumor uptake, and tumor: serum ratios, of B72.3 and CC49 was carried out using the paired T-test. There was no statistically significant difference between absolute tumor uptake of either mAb at either dose though there seemed to be a trend toward relatively improved tumor uptake of “‘I-CC49 at the 20 mg dose. At the 1 mg dose,

12

C. R. DIVGIet al.

Fig. 1. (a) CT scan of patient 5 just before mAb administration showing a solitary right hepatic lobe lesion. (b) SPECT study carried out 5 days after mAb administration. The top left image sequence shows relevant transaxial slices; corresponding coronal slices are shown in the middle panel; and sagittal images are in the bottom left panel. Reference planes are shown on the upper right panel. A 3-D reconstructed volume image is shown in the lower right panel.

there was no difference in average tumor %ID/g between B72.3 and CC49; at the 20 mg dose, 4 of the 5 patients showed greater tumor uptake of CC49 than of B72.3. However, tumor:serum ratios of

r3’I-CC49 were greater than those of *251-B72.3 (P < 0.01) at all dose levels, as well as at individual doses (P < 0.01 at the 1 mg dose and P = 0.05 at the 20mg dose).

Comparison of anti-TAG-72 mAbs in colon cancer

13

Fig. 2. Relevant radionuclide SPECT slices and corresponding CT slices of patient 9 are shown. Upper left panel, transverse SPECT image of the right adrenal lesion; the corresponding CT slice is shown on the bottom left panel; the abnormal left hepatic lobe uptake is shown in the transverse SPECT slice on the upper right panel, with the corresponding (normal) CT slice below.

Discussion Monoclonal antibodies offer unique features of specificity that make them potentially useful in the detection and treatment of cancer. The largest number of mAbs studied to date have been against colorectal cancer (Kramer and Larson, 1991). Studies have shown that radiolabeled mAbs have considerable potential in diagnosis and may be useful as therapeutic agents. The antigenic targets studied most to date have been CEA and TAG-72. However, the expanding number of mAbs against an antigenic target make selection of the ideal mAb difficult. Thus, there is a need for clinical trials that will directly compare two or more mAbs in the same patient group; such trials would then enable selection of the appropriate mAb for future development. We have compared radioiodinated B72.3 and CC49, two mAbs against TAG-72, in 10 pre-surgical patients with metastatic colorectal cancer. These two antibodies have been previously compared in vitro: CC49 is a higher-affinity mAb and generally shows higher specific uptake in xenograft models (Kuroki et al., 1990).

There were no side-effects in the patients studied. Both mAbs showed localization in metastatic colorectal cancer, with no difference in absolute tumor concentration. There was also no difference in serum clearance of either mAb. At the 20mg dose, “‘I-CC49 MAB scans visualized all known lesions 2 1 cm in diameter. At both 1 and 20 mg doses, the tumor: serum ratios of CC49 were significantly greater than those of B72.3. In contrast to the results presented here, the study by Gallinger et al. (1993) showed no significant difference in tumor:non-tumor ratios of B72.3 and CC49 in 8 patients studied. They did not administer more than 2.8 mg of CC49 or B72.3. While we also did not find any difference in absolute tumor uptake of either mAb, we did, however, find higher tumor:serum ratios of CC49 than of B72.3 at the 1 mg dose. We are unable to explain the discrepancy between our results and those of Gallinger et al. at the lower dose level, but feel that the results are valid in light of increased splenic uptake of CC49 reported by both groups. This would have resulted in lower normal tissue concentrations of CC49 with consequent higher tumor: serum ratios. While earlier studies with B72.3 had shown no effect of the

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C.

R. DIVGI

et al.

Table 2. Percent injected dose per gram of tumor (%ID/g) of each mAb in various portions of tumor (where aoolicablel is detailed L.

,

B72.3’

cc49* Patient No. I 2 3

4

5

8 9

10

Mean All doses

%IDk 0.00129 0.00108 0.005 0.00156 0.00243 0.00198 0.0039 0.00139 0.00138 0.00178 0.0088 0.0089 0.0082 0.0085 0.00106 0.0091 0.0052’ 0.0082 0.0111 0.0073 0.0013 0.0019 0.0024 0.00115 0.00104 0.0305 0.00579 0.0031 0.0032 0.0105 0.0055 0.0122 0.0047 0.00178 0.00485 0.00124 0.01269 0.00253 0.00265 0.00195 0.00294 0.00566’ 0.0055

T/serumt 2.1 1.7 4.7 1.6 2.5 2.0 4.0 1.0 1.0 1.3 4.8 4.9 4.5 4.7 5.8 5.0 3.4” 3.3 4.5 3.0 0.6 0.9 1.2 0.6 0.5 8.6 5.4 2.9 3.0 9.7 5.1 11.3 6.0 2.3 6.2 1.6 16.2 3.2 3.4 2.5 3.8 4.3b 4.0”

%ID/g

T/serum

0.00096 0.00162 0.0034 0.00379 0.00424 0.00466 0.00825 0.00507 0.00758 0.00794 0.0038 0.0042 0.0076 0.0061 0.0065 0.0074 0.0053 0.0013 0.0034 0.0042 0.0043 0.0177 0.0067 0.0022 0.0027 0.00243 0.0027 1 0.0011 0.0022 0.0065 0.0023 0.0032 0.00194 0.00109 0.00236 0.00205 0.00305 0.00145 0.00143 0.00154 0.00179 0.0041 0.0046

1.1 1.8 1.8 1.4 1.6 1.8 3.1 1.8 2.7 2.9 0.3 0.3 0.6 0.5 0.5 0.6 1.4 0.3 0.9 1.1 1.6 6.7 2.5 0.8 1.0 4.5 2.2 0.9 1.8 5.2 1.8 2.6 3.0 1.7 3.7 3.2 4.8 2.3 2.2 2.4 2.8 2.7 2.2

*CC49 was labeled with 13’I; 872.3 was labeled with 12’I. tT/serum = %/D/g tumor/%ID/mL serum. ‘P < 0.01; bP = 0.05; ‘not significant. All measurements by paired

milligram dose of mAb upon kinetics or radiolocalization (Esteban et al., 1987), there were preliminary data suggesting that the optimum biologic dose of CC49 was 20mg (J. Schlom, unpublished observation, 1991). We therefore decided to study five more patients at a higher (20 mg) dose of mAb. We are unaware of any other published clinical trial using two (or more) mAbs against a particular cancer, in pre-surgical patients. As mentioned above, such a trial should have several requirements, including radionuclides of the same element, comparable radiolabeling characteristics and no cross-reactivity or competition. We fulfilled all of these criteria: B72.3 and CC49 do not compete with each other (Kuroki et al., 1990); B72.3 was labeled with iz51and CC49 with 13’1,both with comparable stability by the Iodogen method. Using both mAbs at their optimum biological dose is also essential to relevant comparison. The trial was complicated somewhat by the observation that “‘ICC49 appears to be a better imaging

Lesion descriution (R) (L) (R) (R) (R) (R) (R) (R) (R) (R) (R) (R) (R) (R) (R) (R)

lobe lobe lobe lobe lobe lobe lobe lobe lobe lobe lobe lobe lobe lobe lobe lobe

liver liver liver liver liver liver liver liver liver liver liver liver liver liver liver liver

(R) lobe liver (R) lobe liver (R) lobe liver (R) lobe liver (R) lobe liver (R) lobe liver (L) lobe liver (L) lobe liver (L) lobe liver (R) adrenal (R) adrenal (R) adrenal (R) adrenal (R) adrenal (R) adrenal Pelvic recurrence Pelvic recurrence Pelvic recurrence Pelvic recurrence Pelvic recurrence Pelvic recurrence Pelvic recurrence Pelvic recurrence Pelvic fecurrence

T-test.

agent at a dose of 20 mg than at 1 mg. There was no absolute increase in tumor uptake of CC49 compared to B72.3; there was a trend toward increased percent injected dose of CC49 per gram of tumor. Logistic considerations precluded more patients being studied at the 20 mg dose: over 75 more patients would have been required in order to determine whether there was a difference in absolute uptake. However, tumor: serum ratios were significantly better for CC49 compared to B72.3. This implies that the improved contrast with CC49 (as compared to B72.3) would better enable radioimmunodetection of tumor; the relatively lower normal tissue uptake would also result in lowered normal tissue toxicity (for a given dose to tumor) in radioimmunotherapy. We therefore concluded that CC49 was a better mAb for use in the detection and treatment of colorectal cancer. The trial reported here is perhaps a situation where issues regarding design are most critical, i.e. one where the mAbs to be studied are directed against the

Comparison of anti-TAG-72 mAbs in colon cancer same antigen. TAG-72 (albeit against different epitopes). However, this trial design may be used very simply in comparing mAbs against different antigens expressed in the same cancer, e.g. in comparing a mAb against CEA with one against TAG-72. If the OBD of each mAb is known, this should be the dose used in the comparison. While it is theoretically possible to include two nuclides that may be imaged simultaneouslv < (iz31 and 13’1 or “I In and ‘llmIn. for \ example), half-life issues may preclude direct comparisons for any length of time. In such trials, therefore, it is usually possible to image only one of the mAbs to be studied. Biopsy of tumor and normal tissue should therefore be incorporated into trial design to allow quantitation of biodistribution of each of the mAbs being studied. In summary: we have shown that it is technically and logistically feasible to compare two radiolabeled mAbs against the same cancer in patients undergoing biopsy confirmation of tumor; that B72.3 and CC49 show comparable uptake in tumor, with a trend toward improved CC49 tumor uptake at the 20mg dose: and that CC49. with its better tumor: serum ratios, is the preferred mAb for future development for radioimmuno -diagnosis and -therapy.

Colcher D., Carrasquillo J. A., Esteban J. M. et al. (1987) Radiolabeled monoclonal antibody B72.3 localization in metastatic lesions of colorectal cancer patients. Nucl. Med. Biol. 14. 25 l-262.

Corbisiero R. M., Yamauchi D. M., Williams L. E. et al. (1991) Comparison of immunoscintigraphy and computerized tomography in identifying colorectal cancer: individual lesion analysis. Cancer Res. 51, 5704--5711. Divgi C. R., McDermott K.. Johnson D. K. et al. (1991) Detection of hepatic metastases from colorectal carcinoma using indium- 111 (‘I’ In) labeled monoclonal antibody (mAb): MSKCC experience with mAb “‘In-CllO. Nucl. Med. Biol. 18, 705-710. Esteban J. M., Colcher D., Sugarbaker P. et al. (1987) Quantitative and qualitative aspects of radiolocalization in colon cancer patients of intravenously administered MAb B72.3. Int. J. Cancer 39, 50-59. Goldenberg D. M., Deland F., Kim. E. et al. (1978) Use of radiolabeled antibodies to CEA for the detection and localization of diverse cancers by external photoscanning. N. Engl. J. Med. 298, 138441388. Griffin T. W.. Brill A. B., Stevens S. el al. (1991) Initial clinical study of indium-1 1 l-labeled clone 110 anticarcinoembryonic antigen antibody in patients with colorectal cancer. J. (Yin. Oncol. 9, 631-640. Johnson V. G., Schlom J., Paterson A. J. et al. (1986) Analysis of a human tumor-associated glycoprotein (TAG-72) identified by monoclonal antibody B72.3. Cancer Res 46, SSO-Si7.

Kramer E. L. and Larson S. M. (1991) Tumor targeting with radiolabeled antibodv for diagnosis and therauv. Immunol. Allergy Clin: N. Am. 11; 301-339.

References Abdel-Nabi H. H., Schwartz A. N., Goldfogel G. et al. (1988) Colorectal tumors: scintigraphy with “‘In-antiCEA monoclonal antibody and correlation with surgical, histopathologic and immunohistochemical findings, Radiology 166, 747-752.

Abdel-Nabi H., Doerr R. J., Chan H-W. et al. (1990) In-l 1l-labeled monoclonal antibody immunoscintigraphy in colorectal carcinoma: safety, sensitivity, and preliminary clinical results. Radiology 175, 163-171. Beatty J. D., Duda R. B., Williams L. E. et al. (1986) Preoperative imaging of colorectal carcinoma with I” In-labeled anti-carcinoembryonic antigen monoclonal antibody. Cancer Res. 46, 6494-6502. Bischof-Delaloye A., Delaloye B. et al. (1989) Clinical value of immunoscintigraphy in colorectal carcinoma patients: a prospective study. J. Nucl. Med. 30, 1646-1656. Carrasquillo J. A., Sugarbaker P., Colcher D. et al. (1988) Radioimmunoscintigraphy of colon cancer with iodine131-labeled B72.3 monoclonal antibody. J. Nucl. Med. 29, 1022-1030.

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.’

Kuroki M., Fernsten P. D., Wunderlich D. ef al. (1990) Serologic mapping of the TAG-72 tumor-associated antigen employing 19 distinct monoclonal antibodies. Cancer Res. 50, 4872-4879. Lindmo T., Bowen E., Cuttitta F. et al. (1984) Determination of immunoreactive fraction of radiolabeled monoclonal antibody by linear extrapolation to binding at infinite antigen excess. J. Immunol. Methods 72, 77-89. Loevinger R. and Berman M. (1951) Efficiency criteria in radioactivity counting. Nucleonics 9, 26. Mach J. P.. Chatal J. F., Lumbroso J. D. et al. (1983) Tumor localization in patients by radiolabeled monoclonal antibodies against colon carcinoma. Cancer Res. 43, 5593 -5600. Patt Y. Z., Lamki L., Haynie T. M. et al. (1988) Improved tumor localization with increasing dose of indium-11 llabeled anti-carcinoembryonic antigen monoclonal antibody ZCE-025 in metastatic rectal cancer. J. C’lin. Oncol. 6, 1220&1230. Welt S., Divgi C. R., Real F. X. et al. (1990) Quantitative analysis of antibody localization in human metastatic colon cancer: a Phase I study of monoclonal antibody A33. J. Clin. Oncol. 8, 1894-1906.