Bevacizumab for Advanced Breast Cancer

Hematol Oncol Clin N Am 21 (2007) 303–319

HEMATOLOGY/ONCOLOGY CLINICS OF NORTH AMERICA

Bevacizumab for Advanced Breast Cancer Tiffany A. Traina, MDa,*, Hope S. Rugo, MDb, Maura Dickler, MDa a

Department of Medicine, Breast Cancer Medicine Service, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10021, USA b Breast Oncology Clinical Trials Program, University of California, San Francisco Comprehensive Cancer Center, 2356 Sutter Street, 6th Floor, Box 1710, San Francisco, CA 94143, USA

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ignificant advances in breast cancer treatment have occurred with the development of novel biologic therapies that specifically target growth factor receptor signaling pathways. One such pathway is the vascular endothelial growth factor (VEGF) signal transduction pathway, which plays a key role in new blood vessel formation. This process of neovascularization, known as angiogenesis, is important for the growth, maintenance, and metastasis of solid tumors. Bevacizumab (Avastin) is a recombinant humanized monoclonal antibody that targets VEGF, which is one of the central growth factors responsible for tumor angiogenesis. In this article the authors briefly review the role of angiogenesis in breast cancer and discuss the impact of antiangiogenic therapy, namely bevacizumab, on the treatment of this disease.

THE ROLE OF ANGIOGENESIS IN BREAST CANCER Tumor angiogenesis is critical for a cancer to transition from the avascular to the vascular phase [1]. This period of time, termed the ‘‘angiogenic switch,’’ is regulated by the expression of pro-angiogenic factors, such as VEGF, basic fibroblast growth factor, platelet-derived endothelial growth factor, and transforming growth factor b, in addition to microenvironment stimuli, such as hypoxia [2,3]. VEGF, a glycoprotein produced by both normal and neoplastic cells, plays a major role in the regulation of angiogenesis in physiologic (ie, tissue repair) and pathologic conditions [4]. VEGF is a potent mitogen and survival factor for endothelial cells and has significant effects on vascular permeability. Considerable laboratory and indirect clinical evidence has accumulated to support the significant role of angiogenesis in breast cancer development, invasion, metastasis, and progression [5,6].

*Corresponding author. E-mail address: [email protected] (T.A. Traina). 0889-8588/07/$ – see front matter doi:10.1016/j.hoc.2007.03.006

ª 2007 Elsevier Inc. All rights reserved. hemonc.theclinics.com

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VEGF binds to a transmembrane immunoglobulin receptor with an intracellular tyrosine kinase domain. The family of VEGF receptors includes VEGFR-1, VEGFR-2, VEGFR-3, neuropilin-1, and neuropilin-2. Of these, VEGFR-2 is most involved in solid tumor angiogenesis. The binding of VEGF to VEGFR-2 leads to receptor dimerization, tyrosine kinase phosphorylation, and recruitment of intracellular signaling molecules responsible for survival, vascular permeability, migration, and proliferation. Some of the signaling pathways triggered by this mechanism include AKT/PKB, eNOS, MAPK, FAK and paxillin, Ras-Raf-MEK-Erk, and PLC-c. These are shown in Fig. 1 [7]. The VEGF ligand and receptor families are more complicated than it would initially seem. There are several VEGF ligands, including VEGF-A, VEGF-B, VEGF-C, VEGF-D, and placental growth factor (PIGF). Each of these has specific binding preferences for VEGF receptors and exists in multiple isoforms. For example, VEGF-A binds to VEGFR-1 and VEGFR-2, whereas VEGF-B only binds to VEGFR-1. This complex, redundant system may explain one mechanism for the development of resistance to antiangiogenic therapies, such as bevacizumab. Elevated VEGF expression has been associated with decreased relapse-free and overall survival in patients who have both lymph node–positive and lymph node–negative early stage breast cancer [5,8–10]. Several studies support the inverse relationship between VEGF expression and clinical outcomes in breast cancer [11–13]. Taken together with the preclinical data from other human malignancies, VEGF seems to be a rational potential target for the pharmacologic inhibition of tumor angiogenesis. The novel antineoplastic agent bevacizumab was developed with this target in mind.

Fig. 1. Downstream signal transduction pathways associated with activation of the VEGF/ VEGFR pathway. (From Cross MJ, Dixelius J, Matsumoto T, et al. VEGF-receptor signal transduction. Trends Biochem Sci 2003;28:491; with permission.)

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BEVACIZUMAB Early pharmacologic studies of a murine anti-VEGF antibody in xenograft models of cancer demonstrated tumor growth inhibition and improved survival [14–16]. The humanized murine anti-VEGF antibody bevacizumab is composed of a human IgG backbone (93%) and an antigen-binding complementarity-determining region derived from a murine monoclonal antibody (7%). Bevacizumab recognizes and neutralizes all isoforms of human VEGF-A with a dissociation constant (Kd) of 1.1 nmol/L [17,18]. On binding circulating VEGF, bevacizumab prevents the ligand from interacting with its receptor, thereby abrogating the biologic activity of VEGF [17]. Clinical pharmacology studies of bevacizumab have demonstrated a linear pharmacokinetic profile and a long terminal half-life of approximately 21 days (range 11–50 days). The clearance of bevacizumab varied relative to body weight, gender, and tumor burden [19]. The pharmacokinetics of bevacizumab do not seem to be significantly affected by concomitant dosing of cytotoxic agents, such as doxorubicin, carboplatin/paclitaxel, and 5-fluorouracil/ leucovorin/irinotecan. Bevacizumab has now been studied in multiple phase I, II, and III clinical trials and has been shown to improve clinically meaningful outcomes in colorectal, renal, lung, and breast cancers [20–28]. The FDA has approved its use for the first- and second-line treatment of metastatic colon cancer when used in combination with 5-fluorouracil–based chemotherapy.

BEVACIZUMAB MONOTHERAPY IN METASTATIC BREAST CANCER A phase I/II, dose-escalation study was conducted in patients who had metastatic breast cancer to determine the safety, efficacy, and pharmacokinetics of bevacizumab [29]. Seventy five patients who had disease progression after at least one conventional therapy were given bevacizumab at escalating doses of 3 mg/kg, 10 mg/kg or 20 mg/kg every 2 weeks. The overall response rate for bevacizumab monotherapy was 9.3% in this group of previously treated patients. Median time to progression measured 2.4 months and median overall survival measured at approximately 10 months. Overall, bevacizumab demonstrated modest clinical benefit and an acceptable toxicity profile, which differed from that typically associated with cytotoxic chemotherapy. Four patients discontinued treatment because of an adverse event: hypertensive encephalopathy, nephrotic syndrome, proteinuria, and headache associated with nausea and vomiting. Headache was the dose-limiting toxicity observed at 20 mg/kg; grade 3/4 headache occurred in 7% of patients. In this study, 10 mg/kg was determined to be the optimal dose of bevacizumab in breast cancer. The most common grade 3/4 adverse events at 10 mg/kg included hypertension, dyspnea, asthenia, and myalgia. Proteinuria of any degree occurred in 24% of patients; however, grade 3/4 proteinuria was described in less than 3% of patients. No serious cases of bleeding were

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reported. Thrombotic events occurred in three patients; two patients experienced congestive heart failure. Several preclinical studies have suggested that the combination of anti-VEGF therapy with chemotherapy may be synergistic [30–35]. Although the mechanism of this synergy remains to be elucidated, it has been postulated that anti-VEGF agents act to normalize convoluted tumor vasculature, thereby reducing interstitial fluid pressure and allowing for improved drug delivery to solid tumors [36]. Because early safety data of single-agent bevacizumab demonstrated a toxicity profile unique from that of traditional cytotoxic therapy, clinical trials of combination bevacizumab and conventional chemotherapy ensued to exploit the benefits of synergy with nonoverlapping toxicity. COMBINATION THERAPY WITH BEVACIZUMAB IN METASTATIC BREAST CANCER Bevacizumab and Chemotherapy Two large randomized phase III trials of bevacizumab in combination with chemotherapy have been reported to date (Table 1). The first of these compared capecitabine with and without bevacizumab in 462 women who had breast cancer. Eligible patients had anthracycline- and taxane-resistant disease and had received at least one chemotherapy regimen in the metastatic setting or had progression of disease within 12 months of completing adjuvant therapy [25]. Capecitabine was delivered at the same dose and schedule for both treatment arms (2500 mg/m2/d divided twice daily for 14 days followed by a 7-day rest period). Patients randomized to the experimental combination arm received bevacizumab at 15 mg/kg intravenously every 3 weeks. The primary endpoint of the study was progression-free survival. The addition of bevacizumab to capecitabine improved the overall response rate from 9.1% to 19.8% (P ¼ .001). Combination therapy did not significantly prolong progression-free survival in this cohort of pretreated women (4.86 versus 4.17 months, hazard ratio (HR) 0.98, 95% CI 0.77–1.25, P ¼ .857) [25]. Although survival outcomes were not improved with the addition of bevacizumab, the combination was well tolerated and did not seem to worsen Table 1 Randomized phase III data of bevacizumab in combination with chemotherapy Capecitabine (C)  bevacizumab (B) N ¼ 462 C RR PFS OS

9.1% 4.17 months 14.5 months

Paclitaxel (P)  bevacizumab (B) N ¼ 680 CþB a

19.8% 4.86 months 15.1 months

P

PþB

13.8% 6.11 months 25.2 months

29.9%b 11.4 monthsb 28.4 months

Abbreviations: OS, overall survival; PFS, progression free survival; RR, response rate. a P ¼ 0.001. b P<.0001.

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capecitabine-related toxicity for this population previously exposed to multiple chemotherapy regimens. Bevacizumab-related toxicities included hypertension (grade 3, 17.9% versus 0.5% for capecitabine alone), thromboembolic events (grade 2, 5.6% versus 3.7% for capecitabine alone) and proteinuria (grade 1–4, 22.3% versus 7.4% for capecitabine alone). Nine patients in the study developed grade 3 or 4 congestive heart failure or cardiomyopathy, two in the capecitabine alone group (0.9%) and seven in the combination group (3.1%). Significant bleeding was rare, limited to minor mucosal bleeds, and did not differ between treatment arms. Thromboembolic events were uncommon and not significantly different based on therapy (7.3% versus 5.6%) [25]. Investigators proposed that the activity of bevacizumab may have been obscured by the extent of prior therapy in this study population who had highly refractory disease [25]. More advanced stages of breast cancer may have developed redundant angiogenic pathways, making blockade of only one ligand or receptor insufficient for significant clinical benefit. The next randomized phase III study therefore explored combination therapy with bevacizumab in a relatively chemonaı¨ve population. The Eastern Cooperative Oncology Group (ECOG) compared weekly paclitaxel with or without bevacizumab as first-line therapy for patients who had locally recurrent or metastatic breast cancer in ECOG trial 2100 [26]. Preclinical evidence suggests that taxanes have antiangiogenic activity that may be enhanced by low-dose weekly administration [37,38]. The combination of weekly paclitaxel and bevacizumab was selected for its dual antiangiogenic inhibition at a time when breast cancers may be critically dependent on VEGF. Paclitaxel was administered to 715 participants at 90 mg/m2 weekly (3 weeks on, 1 week off). Patients randomized to the combination received bevacizumab at 10 mg/kg every 2 weeks (n ¼ 365). Patients who had HER2-positive breast cancer were excluded from this study unless previously treated with trastuzumab. Other pertinent exclusion criteria included brain metastases and significant underlying heart disease. Patients were permitted to have received adjuvant taxane therapy if a disease-free interval of at least 12 months had elapsed. Patients were stratified according to prognostic factors, such as disease-free interval, number of metastatic sites, exposure to adjuvant therapy, and hormone receptor status. The study was powered to detect a 33% improvement in progression-free survival, the primary endpoint of the study. Treatment arms were well balanced, as expected. Two thirds of patients had received prior adjuvant therapy and nearly 20% had previous taxane therapy. At a second planned interim analysis, the combination of bevacizumab and paclitaxel showed significant improvement in progression-free survival (median, 10.97 months versus 6.11 months, HR 0.498, P < .001). Similarly, the bevacizumab-treated arm demonstrated a higher overall response rate (28.2% versus 14.2%, P < .0001). Overall survival data remain immature; however, at the time of this interim analysis no statistically significant difference had been observed from the addition of bevacizumab (25.2 months versus 28.4 months, HR 0.84 [0.64–1.05], P ¼ .12) [26].

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In this phase III study, bevacizumab-related toxicities were observed; however, the combination of bevacizumab and chemotherapy seemed well tolerated overall. The bevacizumab treatment arm had greater grade 3 or 4 hypertension (15.3% versus 2%, P < .0001), proteinuria (2% versus 0%, P ¼ .002), neuropathy (20.2% versus 14.2%; P ¼ .01), and bleeding episodes (2.3% versus 0%, P ¼ .02). There were no increased thromboembolic events or episodes of congestive heart failure in the combination arm [26]. Several phase II studies are exploring the combination of bevacizumab with additional chemotherapeutics with known activity in breast cancer. For example, 27 patients who had breast cancer were given the combination of bevacizumab (10 mg/kg every 2 weeks) and docetaxel (35 mg/m2 weekly for 3 weeks in a 4-week cycle) as first- or second-line therapy for their metastatic disease [39]. The combination of bevacizumab and docetaxel demonstrated an overall response rate of 52% and median progression-free survival of 7.5 months. Most toxicities were grade 2 or less and were manageable. Most side effects observed were those expected from docetaxel chemotherapy. Hematologic toxicity was notable for grade 3/4 neutropenia (19%) and leukopenia (26%). Grade 3/4 nonhematologic side effects (largely attributed to docetaxel) included fatigue (15%), neuropathy (8%), stomatitis (7%), thrombosis (7%), and arthralgia (7%). The bevacizumab-related adverse events were minor and similar to those previously reported in larger studies, with the exception of serious hypertension, which occurred in only 1 patient (4%) as compared with approximately 11% to 18% of patients. A total of 33% of patients discontinued treatment for reasons such as pulmonary embolism (n ¼ 2), grade 3 hypertension (n ¼ 1), serious bacterial infection (n ¼ 1), pleural effusion (n ¼ 1), dyspnea (n ¼ 1), and neuropathy (n ¼ 1) [39]. Burstein and colleagues [40] have completed a single-institution, phase II trial of bevacizumab in combination with vinorelbine for refractory advanced breast cancer. Eligible patients were permitted no more than two prior chemotherapy regimens for metastatic disease. A total of 56 study participants received bevacizumab (10 mg/kg every 2 weeks) and vinorelbine (25 mg/m2 weekly) until disease progression or unacceptable toxicity. The overall response rate was 31% and as high as 42% in patients receiving the combination as first-line therapy. Bevacizumab with vinorelbine seemed feasible with modest side effects, such as hypertension (grade 2 or less), epistaxis, proteinuria, and thrombosis [40]. These data support that combination antiangiogenic therapy with chemotherapy is generally well tolerated and may demonstrate greater efficacy in less refractory patients or with other chemotherapy agents. Additional ongoing phase II trials test the feasibility and efficacy of bevacizumab in combination with several other chemotherapy regimens. A randomized phase II trial is studying bevacizumab in combination with nanoparticle albumin-bound (nab) paclitaxel given either weekly, every 2 weeks, or every 3 weeks. Other trials explore the combination of bevacizumab with nab-paclitaxel and carboplatin [41], nab-paclitaxel and gemcitabine [42], and low-dose repetitive ‘‘metronomic’’ chemotherapy with oral cyclophosphamide and

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methotrexate [43]. Preliminary data from these trials suggest the combinations are feasible and worthy of further efficacy trials. Bevacizumab with Endocrine Therapy The justification for combining a novel therapy that targets angiogenesis with conventional cytotoxic therapies seemed reasonable given preclinical data, the activity of bevacizumab as monotherapy, and the distinctly different toxicity profile of this biologic when compared with most chemotherapy agents. In a similar way, preclinical evidence suggests that the combination of bevacizumab with endocrine therapy may prove to be a clinically advantageous approach. Estrogen is a potent modulator of angiogenesis and has been shown to directly regulate new blood vessel formation through effects on endothelial cells in physiologic and pathologic conditions. In the human menstrual cycle, the microvascular blood supply of the adult endometrium undergoes cyclical benign neovascularization under the control of ovarian steroids. Additional in vitro evidence supports this important role of estrogen. Endothelial cell proliferation and migration is increased by estrogen exposure in human umbilical vein endothelial cell cultures [44]. Estrogen-induced angiogenesis is mediated by VEGF [45,46] and estrogen withdrawal reduces VEGF expression in oophorectomized animal models [47]. In MCF-7 breast cancer cell lines, estrogen increases levels of VEGF protein [48] and aromatase inhibition in a carcinogen-induced mouse model lowered VEGF expression [49]. Provocative work from Jain and colleagues [50] strongly supports the role for hormonal modulation of angiogenesis. He and his colleagues developed a model for observing angiogenesis in vivo and demonstrated that castration of a mouse with androgen-dependent breast cancer led to tumor and blood vessel regression. The initial response to castration was followed by the development of endocrine resistance and ultimately tumor regrowth and neovascularization. This second wave of angiogenesis was shown to depend on VEGF. These observations mirror what many patients who have initially hormone-sensitive breast cancers experience. Despite an upfront response to endocrine manipulation, inevitably most patients become refractory to hormonal therapies in the metastatic setting [50]. Anti-VEGF therapy may delay resistance to endocrine therapy in patients who have hormone-sensitive breast cancer. In a feasibility study of combination anti-VEGF and endocrine therapy, bevacizumab and letrozole were given to eligible patients who had hormone receptor–positive, metastatic, or locally advanced breast cancer. Study participants were postmenopausal or underwent ovarian suppression. Prior use of a nonsteroidal aromatase inhibitor without progression of disease was permitted because safety was the primary endpoint of the trial. Forty three women received letrozole 2.5 mg orally daily and bevacizumab 15 mg/kg intravenously every 3 weeks. Patients were evaluated for toxicity every 3 weeks and for response after every 12 weeks [51,52].

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In a preliminary report of this trial, the most common grade 2 or 3 toxicities associated with this regimen were hypertension (21%/16%), headache (14%/ 5%), proteinuria (5%/5%), and fatigue (14%/2%). Greater than 80% of study participants received a nonsteroidal aromatase inhibitor as first-line therapy of metastatic breast cancer for a median of 18 weeks (range, 1–216) before study entry [51]. This confounds the ability to draw conclusions regarding efficacy; however, to date the combination of letrozole and bevacizumab seems well tolerated and feasible. This has led to a planned multicenter randomized phase III trial of first-line endocrine therapy with or without bevacizumab within the Cancer and Leukemia Group B. Treating physicians will have the choice of endocrine therapy (either aromatase inhibition or tamoxifen). The North Central Cancer Treatment Group will be investigating fulvestrant, an estrogen receptor down-regulator with bevacizumab. Bevacizumab and Other Targeted Therapies Numerous redundant signal transduction pathways may explain resistance to monotherapy strategies and argue for combinations of anti-VEGF therapy. In addition to coadministration with chemotherapy and endocrine therapy, bevacizumab is being studied in combination with other novel treatments that target pathways responsible for cell growth and survival. Data suggest an association between the human epidermal growth factor receptor-2 (HER2) and the VEGF-R signaling pathways at the molecular level [10,53]. The gene for HER2 (erbB-2) is amplified or the HER2 protein is overexpressed in approximately 20% to 30% of all breast cancers and confers a more aggressive phenotype than HER2 normal cancers [54,55]. Transcriptional up-regulation of VEGF in HER2-overexpressing breast cancers has been reported and investigators postulate that this may contribute to the aggressive phenotype observed in HER2-positive breast cancers. Preclinical work supports that overexpression of HER2 leads to increased expression of VEGF at the RNA and protein levels in vitro. Moreover, blockade of the HER2 signaling pathway through antibody-mediated inhibition of the receptor significantly decreases VEGF levels [56]. These data provided a rationale for testing the combination of bevacizumab with trastuzumab, a humanized monoclonal antibody that selectively targets the extracellular domain of HER2, in women who had HER2-positive breast cancer [10]. An open-label phase I dose-escalation trial of bevacizumab and trastuzumab identified the recommended phase II doses for these agents when given together. Preliminary data suggest that coadministration does not alter the pharmacokinetics of either bevacizumab or trastuzumab. Of the nine patients treated, five are reported to have clinical responses with minimal toxicity. The combination of anti-VEGF and anti-HER2 therapy seems worthy of further study. Several small molecules have been created to target signal transduction pathways responsible for cell growth, apoptosis, and angiogenesis. An example of such an agent is erlotinib (Tarceva), which binds to the epidermal growth factor receptor (EGFR) and inhibits its intracellular tyrosine kinase.

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Anti-EGFR therapy may inhibit angiogenesis [57] by decreasing synthesis of angiogenic proteins from tumor cells and by disrupting autocrine and paracrine loops that exist between tumor cells and tumor-associated endothelial cells [2]. To test the combination of anti-VEGF and anti-EGFR therapy, 38 patients who had metastatic breast cancer were treated on a single-arm phase II study with erlotinib and bevacizumab after having received at least one prior chemotherapy regimen for their disease. One patient achieved a partial response and continues on therapy at more than 36 months. Although the combination had manageable toxicities, such as hypertension, diarrhea, rash, and nausea, the dual angiogenic inhibition had limited activity in patients who had previously treated metastatic breast cancer. These efficacy data reflect the importance of identifying biologically relevant targets and confirming their presence in study populations. It also highlights the need for identifying predictors of response to therapy as targeted agents are incorporated in treatment plans. BEVACIZUMAB-ASSOCIATED TOXICITY Anti-VEGF targeted therapy is generally well tolerated; however, bevacizumab use is associated with rare but serious toxicities. The cause of these side effects is poorly understood but may become increasingly clear as large randomized trials investigating multiple tumor types pay special attention to these issues. In this article, the authors briefly discuss a selection of the rare toxicities unique to anti-VEGF therapy. Side effects reported with bevacizumab are listed in Table 2. These are easily managed and rarely require bevacizumab discontinuation. In Phase I and II clinical trials, four potential bevacizumab-associated side effects were identified: hypertension, proteinuria, venous and arterial thromboembolic events, and hemorrhage. Randomized studies in patients who have metastatic malignancies further defined the safety profile of bevacizumab and identified additional side effects that may be attributable to anti-VEGF therapy. These include congestive heart failure (CHF) in patients who have had prior exposure to anthracyclines, gastrointestinal perforation, and wound healing complications. Hypertension is common in patients treated with bevacizumab, with an incidence of 20% to 30% across trials [25,26,29]. Blood pressure elevation can often be managed with initiation or increase of routine oral antihypertensive medications. Incidents of hypertensive crisis with encephalopathy or cardiovascular sequelae have been rarely reported. The mechanism of anti-VEGF–induced hypertension is unknown although it has been postulated that inhibition of nitric oxide release plays a part in driving higher systemic pressures [58]. Blood pressure should be closely monitored during bevacizumab therapy and treatment should be suspended in the event of uncontrolled hypertension. Proteinuria has been observed in nearly all bevacizumab studies to date, ranging in severity from an asymptomatic increase in urine protein (incidence of about 20%) to rare instances of nephrotic syndrome (0.5% incidence). Pathologic findings on renal biopsies in two patients have shown

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Table 2 Side effects reported with bevacizumab Infusion reaction Constitutional Skin Gastrointestinal

Cardiovascular

Hematologic Hepatic Neurologic

Renal/genitourinary Pulmonary Musculoskeletal

Fever, chills, rigor, rash, urticaria, dyspnea Headache, infection without neutropenia, asthenia Rash, urticaria, delayed wound healing, pruritus Nausea, vomiting, colitis, stomatitis, intestinal obstruction Hypertension, hypotension, pericardial effusion, decrease in cardiac function, cardiac troponin I elevation Arterial and venous thrombosis, hemorrhage Liver function test abnormalities Dizziness, leukoencephalopathy syndrome, including reversible posterior leukoencephalopathy syndrome Proteinuria, nephrotic syndrome Pulmonary infiltration, dyspnea Arthralgia, chest pain

membranoproliferative glomerulonephritis. Overall, the incidence of National Cancer Institute-Common Terminology Criteria for Adverse Effects grade 3 proteinuria (>3.5 g/24-h urine) is low (<2%); however, it may be exacerbated by the use of other nephrotoxic agents, such as bisphosphonate therapy, in this patient population. Patients who experienced proteinuria while receiving the combination of bevacizumab and capecitabine seemed to be more likely to report hypertension [25]. To date, the safety of continuing bevacizumab in patients who have moderate or severe proteinuria has not been adequately tested. A random urine protein to urine creatinine ratio (UPC ratio) should be monitored routinely in patients receiving bevacizumab to assess for proteinuria. Venous and arterial thromboembolic events, ranging in severity from catheter-associated phlebitis to fatal arterial clots, have been reported in patients treated with bevacizumab. The risk for arterial thromboembolic events is increased with bevacizumab therapy, and such events included cerebral infarction, transient ischemic attack, myocardial infarction, and peripheral arterial

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thrombosis. In the pivotal trial in colorectal cancer, the incidence of arterial thromboembolic events was 1% in the control arm compared with 3% in the bevacizumab-containing arm [21]. The incidence of any arterial or venous thrombotic event was greater in the bevacizumab-containing arm (16.2% versus 19.4%) although this did not meet statistical significance [21]. A pooled analysis of five randomized studies showed a twofold increase in these events (4.4% versus 1.9%). Baseline characteristics, such as age greater than 65 years and prior arterial ischemic events, seem to confer additional risk for thrombosis. In the randomized trial of capecitabine with or without bevacizumab in patients who have metastatic breast cancer, the incidence of venous thrombotic events was rare and similar between both treatment arms (5.6% versus 7.3%) [25]. Bevacizumab in combination with paclitaxel led to infrequent thromboembolic events of similar incidence as with chemotherapy alone [26]. As we look toward combination regimens with bevacizumab to improve on efficacy, we must carefully monitor patients receiving multiple thrombogenic agents (ie, tamoxifen, other anti-VEGF targeted therapies). The incidence of hemorrhage is also increased with bevacizumab therapy. Epistaxis and minor mucosal bleeding are most common, occurring in 20% to 40% of patients, but bleeding is generally mild and rarely requires medical intervention. Life-threatening and fatal hemorrhagic events have been observed in bevacizumab studies and included pulmonary hemorrhage, central nervous system bleeding, and gastrointestinal bleeding. In a phase II study in non–small cell lung cancer, six cases of life-threatening hemoptysis occurred in patients who had central cavitary lesions of squamous cell histology among the 66 patients treated with bevacizumab and chemotherapy; four of these events were fatal [24]. In the pivotal phase III trial in advanced colorectal cancer, the rate of any gastrointestinal hemorrhage was 24% in the bevacizumab arm compared with 6% in the control arm. In the large randomized trials of bevacizumab in breast cancer, serious grade 3 bleeding was rare and not statistically different between treatment groups. Gastrointestinal perforations and fistulae were rare but serious adverse events that occurred at an increased rate in bevacizumab-containing therapies. Most of such events required surgical intervention and some were associated with a fatal outcome. In the pivotal phase III trial in colorectal cancer, the incidence of bowel perforation was 2% to 4% in patients receiving chemotherapy with bevacizumab and 0.3% in patients receiving chemotherapy alone [21]. Intestinal perforation has also been reported in patients who have gastric cancer, pancreatic cancer, ovarian cancer, or nonmalignant conditions, such as diverticulitis and peptic ulcer. Physicians administering bevacizumab should maintain a low threshold to consider gastrointestinal perforation in patients who develop abdominal pain while on bevacizumab therapy. Bevacizumab delays wound healing in animal models and may also compromise or delay wound healing in patients. Bowel anastomotic dehiscence and skin wound dehiscence have been reported in clinical trials with bevacizumab. The appropriate interval between surgery and initiation of bevacizumab

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required to avoid the risk for impaired wound healing has not been determined; however, all clinical trials with bevacizumab have required a minimum of 28 days from prior major surgery. The optimal interval between termination of bevacizumab and subsequent elective surgery has not been determined either. Decisions on the timing of elective surgery should take into consideration the half-life of bevacizumab (average 21 days, with a range of 11–50 days) [21,59]. In the breast cancer population, as bevacizumab is explored in the neoadjuvant and adjuvant settings, the timing of breast reconstruction relative to last bevacizumab dose must be carefully considered. Recently, a phase II trial of neoadjuvant docetaxel with or without bevacizumab reported delayed wound healing (as measured by a delay in beginning radiation therapy) in 8 of 49 patients. Although more patients treated with bevacizumab experienced delayed wound healing, there was no statistically significant difference between treatment arms (5 patients versus 3 patients, P ¼ .691) [60]. The association between bevacizumab treatment and cardiac dysfunction remains uncertain. Some patients receiving bevacizumab have experienced cardiac toxicity ranging from asymptomatic declines in left ventricular ejection fraction (LVEF) to symptomatic CHF. It is not yet known whether bevacizumab potentiates the cardiac toxicity of anthracyclines. In a phase I/II trial of bevacizumab in metastatic breast cancer, 2 of the 75 (3%) women developed CHF. Both of these women had received prior anthracycline and chest wall radiation, however [29]. Similarly, the study of capecitabine with or without bevacizumab did note an increase in grade 3 and 4 cardiac toxicity on the bevacizumab-containing arm (7/229 versus 2/215). Half of the patients who experienced grade 3 or 4 cardiac toxicity had a baseline LVEF less than 50% [25]. All patients had received prior anthracycline treatment and three of the seven had radiation therapy to the left chest wall in the past. Because routine evaluation of LVEF was not required by that trial, it cannot be determined whether there was also an increase in grade 2 toxicity. This has raised the possibility that bevacizumab may exacerbate or potentiate anthracycline-induced cardiomyopathy. Bevacizumab in combination with mitoxantrone and cytosine arabinoside was evaluated in patients who had relapsed or poor risk leukemia who had baseline LVEF greater than 45% [61]. There were two cases of fatal cardiomyopathy in this study. Ten percent (5/48) of patients had decreases in LVEF from greater than 50% to between 30% and 35% (two grade 1, two grade 2, one grade 4). Some 92% of subjects had previously received substantial cumulative doses of anthracyclines and 30% of those who had cardiac toxicity had mantle radiation for prior Hodgkin’s disease. LVEF returned to normal in three of five patients after 2 to 4 weeks. The possible reversible nature of this cardiac toxicity is supported by data from a study of bevacizumab in combination with doxorubicin for soft tissue sarcoma. In this trial, patients who had not had prior anthracycline or chest radiation and had baseline LVEF greater than 50% received doxorubicin 75 mg/m2 concurrently with bevacizumab 15 mg/m2 every 3 weeks (with the

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addition of dexrazoxane if doxorubicin exceeded 300 mg/m2). LVEF was assessed every two cycles while on trial. The overall toxicity of the combination was similar to single agent doxorubicin with the exception of cardiac toxicity. The reported rates of cardiomyopathy from doxorubicin are 1% to 2% for a cumulative doxorubicin dose less than 300 mg/m2. In this study, LVEF declined significantly in 35% of patients (6/17) [62]. Four patients had grade 2 declines in LVEF after 1, 2, 4, and 4 cycles of combination therapy. Grade 2 is defined as an asymptomatic decline below the lower limit of normal or a decline greater than 20%. One patient each experienced grade 3 (symptomatic CHF) and grade 4 (severe/refractory CHF) cardiotoxicity with combination therapy. Cardiac toxicity was often reversible. Among the six patients who had decreased LVEF, follow-up demonstrated improvement of LVEF in five. A phase II trial of neoadjuvant docetaxel with or without bevacizumab followed by local therapy and adjuvant doxorubicin and cyclophosphamide for four cycles (AC4) did not demonstrate declines in LVEF for women who had early stage breast cancer [63]. Preliminary data from a study of neoadjuvant doxorubicin and docetaxel in combination with bevacizumab every 3 weeks for 6 cycles indicated a 10% rate of asymptomatic decline in LVEF (2/21 patients) but no symptomatic CHF. All LVEF declines normalized on follow-up evaluation [64]. Similarly, in the randomized Phase III trial of more than 600 women who had metastatic breast cancer receiving paclitaxel with or without bevacizumab, there was no difference seen in rate of CHF (0.3% versus 0%) [65]. The risk for cardiotoxicity to patients receiving left breast/chest radiation and bevacizumab is unknown. Bevacizumab is believed to potentiate the effects of radiation therapy in the neoadjuvant treatment of rectal cancers; however, it is unclear if bevacizumab adds to radiation-induced toxicity. This is currently being studied by Zhu and Willett [66,67]. Bevacizumab may act as a radiation sensitizer for those patients receiving concurrent therapies for their breast cancer. In summary, if bevacizumab plays a role in treatment-related cardiotoxicity, it remains to be proven. Finally, a rare side effect of bevacizumab recently identified is reversible posterior leukoencephalopathy syndrome (RPLS). RPLS or clinical syndromes related to vasogenic edema of the white matter have been reported in less than 1% of patients treated with bevacizumab. Clinical presentations are variable and may include altered mental status, seizure, and cortical visual deficit. Hypertension is a common risk factor and was present in most patients on bevacizumab who developed RPLS. MRI scans are critical for diagnosis and typically demonstrate vasogenic edema predominantly in the white matter of the posterior parietal and occipital lobes. Less frequently, the anterior distributions and the gray matter may also be involved. RPLS should be in the differential diagnosis in patients presenting with unexplained mental status changes, visual disturbance, seizure, or other central nervous system findings. RPLS is potentially reversible, but timely correction of the underlying causes, including blood pressure control, and interruption of the offending agent is important to prevent progression to irreversible tissue damage.

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SUMMARY Antiangiogenic therapy is a promising addition to the cache of metastatic breast cancer treatments. The efficacy and manageable toxicity profile of bevacizumab support its use in combination with chemotherapy for advanced breast cancer. Studies are underway in the metastatic setting to explore bevacizumab in combination with hormone therapy and with other agents that target the HER2 and VEGF pathways. In addition, studies are ongoing to test bevacizumab in the adjuvant setting with anthracycline- and taxane-based chemotherapy. Large neoadjuvant trials are exploring the use of bevacizumab with conventional chemotherapy regimens and with metronomic low-dose cyclophosphamide and methotrexate. As we begin to incorporate antiangiogenic therapies in our approach to patients who have breast cancer, there is an urgent need for biomarkers to guide anti-VEGF therapy. Ongoing efforts to develop robust surrogate markers of response are critical in guiding appropriate patient selection for this novel yet costly therapy with rare but serious toxicities. References [1] Hanahan D, Folkman J. Patterns and emerging mechanisms of the angiogenic switch during tumorigenesis. Cell 1996;86(3):353–64. [2] Kerbel R, Folkman J. Clinical translation of angiogenesis inhibitors. Nat Rev Cancer 2002;2(10):727–39. [3] Rosen LS. Clinical experience with angiogenesis signaling inhibitors: focus on vascular endothelial growth factor (VEGF) blockers. Cancer Control 2002;9(2 Suppl):36–44. [4] Ferrara N. Role of vascular endothelial growth factor in the regulation of angiogenesis. Kidney Int 1999;56(3):794–814. [5] Gasparini G. Breast cancer: molecular genetics, pathogenesis and therapeutics. In: Bowcock A, editor. Angiogenesis in breast cancer. Role in biology, tumor progression, and prognosis; Totowa (NJ): Humana Press, Inc.; 1999. p. 347–71. [6] Warren RS, Yuan H, Matli MR, et al. Regulation by vascular endothelial growth factor of human colon cancer tumorigenesis in a mouse model of experimental liver metastasis. J Clin Invest 1995;95(4):1789–97. [7] Cross MJ, Dixelius J, Matsumoto T, et al. VEGF-receptor signal transduction. Trends in Biochemical Sciences 2003;28(9):488–94. [8] Relf M, LeJeunes, Scott PA, et al. Expression of the angiogenic factors vascular endothelial cell growth factor, acidic and basic fibroblast growth factor, tumor growth factor beta-1, plateletderived endothelial cell growth factor, placenta growth factor, and pleiotrophin in human primary breast cancer and its relation to angiogenesis. Cancer Res 1997;57(5):963–9. [9] Sledge GW Jr. Vascular endothelial growth factor in breast cancer: biologic and therapeutic aspects. Semin Oncol 2002;29(3 Suppl 11):104–10. [10] Konecny GE, Meng YG, Untch M, et al. Association between HER-2/neu and vascular endothelial growth factor expression predicts clinical outcome in primary breast cancer patients. Clin Cancer Res 2004;10(5):1706–16. [11] Linderholm B, Tavelin B, Grankvist K, et al. Vascular endothelial growth factor is of high prognostic value in node-negative breast carcinoma. J Clin Oncol 1998;16(9):3121–8. [12] Linderholm B, Grankvist K, Wilking N, et al. Correlation of vascular endothelial growth factor content with recurrences, survival, and first relapse site in primary node-positive breast carcinoma after adjuvant treatment. J Clin Oncol 2000;18(7):1423–31. [13] Foekens JA, Peters HA, Grebenchtchikov N, et al. High tumor levels of vascular endothelial growth factor predict poor response to systemic therapy in advanced breast cancer. Cancer Res 2001;61(14):5407–14.

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