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Originally published as JCO Early Release 10.1200/JCO.2007.14.5375 on March 17 2008 © 2008 American Society of Clinical Oncology. Phase II Study of Sunitinib Malate, an Oral Multitargeted Tyrosine Kinase Inhibitor, in Patients With Metastatic Breast Cancer Previously Treated With an Anthracycline and a Taxane
From the Dana-Farber Cancer Institute, Boston, MA; University of Colorado Health Sciences Center, Denver, CO; University of California San Francisco, San Francisco; California Cancer Care Inc, Greenbrae; Pfizer Inc, La Jolla; TRACON Pharmaceuticals Inc, San Diego, CA; Rush University Medical Center, Chicago, IL; Sidney Kimmel Cancer Center at Johns Hopkins, Baltimore, MD; and the Indiana University Simon Cancer Center, Indianapolis, IN Corresponding author: Harold J. Burstein, MD, PhD, Dana-Farber Cancer Institute, 44 Binney St, Boston, MA, 02115; e-mail: hburstein{at}partners.org
Purpose Sunitinib is an oral, multitargeted tyrosine kinase inhibitor that inhibits vascular endothelial growth factor receptor (VEGFR), platelet-derived growth factor receptor, stem cell factor receptor (KIT), and colony-stimulating factor-1 receptor. This phase II, open-label, multicenter study evaluated sunitinib monotherapy in patients with metastatic breast cancer (MBC). Patients and Methods Sixty-four patients previously treated with an anthracycline and a taxane received sunitinib 50 mg/d in 6-week cycles (4 weeks on, then 2 weeks off treatment). The primary end point was objective response rate. Plasma samples were obtained for pharmacokinetic and biomarker analysis.
Results Seven patients achieved a partial response (median duration, 19 weeks), giving an overall response rate of 11%. Three additional patients (5%) maintained stable disease for Conclusion Sunitinib is active in patients with heavily pretreated MBC. Most AEs were of mild-to-moderate severity and manageable with supportive treatment and/or dose modification. Further studies in breast cancer are warranted.
Treatment options for advanced breast cancer include chemotherapy, antiestrogen interventions, and HER2-directed therapy. Despite the success of these strategies, there is a persistent need for novel and improved therapeutic approaches. Substantial preclinical and indirect clinical evidence has shown that angiogenesis plays an essential role in breast cancer development, invasion, and metastasis.1,2 Multiple angiogenic factors, including vascular endothelial growth factor (VEGF), are commonly overexpressed by invasive breast cancers.3,4 Studies have shown that certain breast carcinoma cells directly express VEGF receptor (R)-1 and VEGFR-2,5,6 with enhanced VEGFR-2 activation observed in malignant breast cancer tissue.7 VEGF functions are mediated by binding to one of three receptor tyrosine kinases: VEGFR-1 (flt-1), VEGFR-2 (flk-1/kdr), and VEGFR-3 (flt-4).8 VEGF is not the only clinically relevant mediator of angiogenesis in breast cancer; platelet-derived growth factor (PDGF) is another angiogenic growth factor contributing to progression of breast cancer cells through autocrine and paracrine mechanisms. Immunohistochemical studies of breast cancer specimens have shown PDGF expression in cancer cells and PDGF receptor (PDGFR- and PDGFR-β) expression predominantly in stromal cells, signifying a paracrine mechanism for tumor development or maintenance.9,10 In addition, elevated PDGF levels in plasma and increased PDGF expression in breast tumor tissues correlate with an increased incidence of metastasis, lower response to chemotherapy and shorter patient survival time.11,12 Overexpression of stem cell factor receptor (KIT), a member of the PDGFR receptor subfamily, has also been documented in breast cancer.13 Colony-stimulating factor-1 expressed by breast cancer cells can stimulate tumor-associated macrophages to secrete important growth factors for breast cancers, including epidermal growth factor, interleukin-6, and transforming growth factor-β.14 Taken together, this evidence highlights tumor angiogenesis as an attractive therapeutic target.15
Sunitinib malate is an oral tyrosine kinase inhibitor that targets several receptor tyrosine kinases, including VEGFR (VEGFR-1, VEGFR-2 and VEGFR-3), PDGFR (PDGFR-
Patients The study population comprised women ( 18 years of age) with a histologically or cytologically confirmed MBC diagnosis. All patients were to have had unidimensionally measurable disease and previous treatment with an anthracycline and a taxane in the adjuvant and/or advanced disease setting (patients only treated in the adjuvant setting must have experienced relapse or disease progression during treatment or within 12 months of the last dose of adjuvant therapy). Anthracycline and taxane treatment could be administered concurrently or sequentially. Patients could have received up to two nonanthracycline or nontaxane chemotherapy regimens in the advanced disease setting, resulting in up to four previous chemotherapy regimens. Prior hormone therapy and immunotherapy were permitted, as were surgery and radiation therapy, provided that they did not affect the only areas of measurable disease. In addition, patients were required to have Eastern Cooperative Oncology Group performance status of 0 or 1, and to have completed all prior chemotherapy and radiotherapy at least 3 weeks before study entry. Patients on bisphosphonate therapy for metastatic bone disease must have initiated therapy 3 months before study entry. All patients had adequate hematologic, hepatic, renal, and cardiac function, and had provided written, informed consent. The main exclusion criteria were prior treatment with tyrosine kinase inhibitors or antiangiogenic agents, radiation to more than 25% of bone marrow, or high-dose chemotherapy requiring hematopoietic stem cell rescue. This study was performed in accordance with the International Conference on Harmonization Good Clinical Practice guidelines, the Declaration of Helsinki (1996 version), and applicable local regulatory requirements and laws. The study was approved by the institutional review board or independent ethics committee of each participating center.
Study Design
Administration of Study Treatment
Assessments The response to sunitinib treatment was evaluated by the investigator based on objective tumor assessments using RECIST.22 Adverse events (AEs) were assessed and AE severity was graded in accordance with the Cancer Therapy Evaluation program, Common Terminology Criteria for AEs, version 3.0. Sunitinib and SU12662 concentrations were analyzed using a validated, sensitive, and specific isocratic liquid chromatographic tandem mass spectrometric method, as previously described.23 Assay reproducibility and accuracy (expressed as coefficient of variation [CV%] and bias % of quality control samples, respectively) ranged from 2.2% to 6.9% and –7.3% to 0.3%, respectively, for sunitinib, and from 4.0% to 10.4% and –4.7% to 2.4%, respectively, for SU12662. Total drug concentrations were calculated as the sum of sunitinib + SU12662 concentrations.
Plasma levels of four putative biomarkers were analyzed with validated enzyme-linked immunosorbant assay kits or kit components (R&D Systems, Minneapolis, MN). For the biomarker descriptive results, a cut point of
Statistical Methods
Patient Characteristics A total of 64 patients were enrolled in the study. Patient characteristics at baseline are summarized in Table 1. In 42% of patients (n = 27), tumors were negative for estrogen receptor (ER) overexpression; HER2 was overexpressed in 19% of patients (n = 12). Nearly one third of patients (31%; n = 20) had tumors that were negative for ER, progesterone receptor, and HER2 overexpression. Of the 12 patients with HER2-positive tumors, eight received previous treatment with trastuzumab. All patients had received prior chemotherapy; 95% had received both an anthracycline and a taxane. Three patients had not received previous taxane treatment (Table 1). The most common sites of metastatic disease were lymph nodes, liver, lung, and bone.
All 64 patients received at least one dose of sunitinib and were included in efficacy and safety analyses. Patients received a median of two treatment cycles (range, 1 to 8). Dose interruption during at least one cycle was required in 33 patients (52%). Twenty-five patients (39%) required dose reduction. AEs were the reason for dose interruption or reduction in 36 patients (56%). The median number of days on treatment was 70.5 (range, 1 to 336), and the median relative dose intensity (relative to assigned dose for each cycle) was 84% (range, 3.6% to 107.1%). One patient completed eight cycles of treatment and received additional therapy under a continuation protocol. Patient discontinuation was primarily due to progressive disease (n = 59; 92%). No patients were considered to have discontinued due to AEs.
Activity
Neither steroid receptor nor HER2 status appeared to correlate with clinical response. Among the patients with triple negative tumors, the response rate was 15% (three responses in 20 patients), and in HER2-positive, trastuzumab-treated tumors the response rate was 25% (three responses in 12 patients).
Safety
Biomarkers Plasma levels of the soluble biomarkers VEGF, soluble VEGFR-2 (sVEGFR-2), soluble VEGFR-3 (sVEGFR-3), and soluble KIT (sKIT) were measured at baseline and serially during treatment.24 Significant changes (P < .00005) in the mean plasma levels of all four biomarkers were seen within the first cycle of sunitinib treatment. At the end of the first cycle, concentrations of VEGF increased to more than three times baseline levels in 32 (73%) of 44 patients, sVEGFR-2 levels decreased by 30% in 45 (88%) of 51 patients, and sVEGFR-3 concentrations decreased by 30% in 42 (82%) of 51 patients (Fig 2). Levels of each of these three markers displayed a cyclical effect coinciding with the sunitinib dosing schedule, with levels returning to near baseline concentrations at the end of the 2-week off-treatment period (Fig 2). During the first cycle, concentrations of sKIT decreased by 30% in 31 (62%) of 50 patients, and levels continued to decrease over time (up to eight cycles), regardless of off-treatment periods.
Some changes in soluble protein levels correlated with TTP and OS. Decreases in sVEGFR-3 levels of 20% at the start of cycle 2 (or at the start of the last treatment cycle) were associated with a trend for longer OS compared with decreases in sVEGFR-3 levels of less than 20% (median not reached [NR], 95% CI, 45.1 to NR v 37.6 weeks, 95% CI, 29.9 to NR; P = .07). The threshold of 20% approximated the mean/median reduction observed at cycle 2, day 1 (approximately 12%). Decreases in sKIT levels by 50% at the start or end of the last treatment cycle were also associated with significantly longer TTP (median, 22.1 weeks; 95% CI, 17.0 to 30.0 v 10.1 weeks; 95% CI, 7.9 to 10.1; P < .0001) and OS (median, 62.6 weeks, 95% CI, 53.1 to NR v 36.0 weeks, 95% CI, 28.4 to NR; P = .0194), compared with sKIT level decreases of less than 50%. The threshold of 50% in this analysis approximated the mean/median reduction observed at cycle 2, day 28 (approximately 46%).
Pharmacokinetics
This study evaluated sunitinib activity and safety in patients with MBC. The clinical benefit rate with sunitinib treatment was 16%, with 11% of patients (n = 7) achieving a PR. Of note, clinical activity was seen irrespective of HER2 and ER status. Response rates of 15% in cases of triple-negative tumors, and 25% in trastuzumab-treated, HER2-positive tumors constitute provocative findings, given the limited treatment options available for such patients. The safety profile of sunitinib in this study was similar to that of other single-agent sunitinib studies in patients with advanced cancer. The most frequently reported AEs were fatigue, nausea, diarrhea, mucosal inflammation, and anorexia. Most AEs were mild to moderate (grades 1 to 2) in severity. Grade 3/4, transient neutropenia was experienced by 34% of patients. This compares with 12% of patients with renal cell carcinoma and 10% of patients with gastrointestinal stromal tumors.25,26 The higher incidence of neutropenia reported here may be due to the heavily pretreated nature of the study population. Fifty-six percent of patients had their dose interrupted or reduced as a result of an AE, but none was considered to have discontinued treatment due to an AE. Careful monitoring of toxicity, with appropriate dose reduction from 50 to 37.5 or 25 mg, may be warranted in patients with advanced breast cancer, and such doses may prove necessary for administering this agent with chemotherapy. In preclinical models, sunitinib administration resulted in a significant reduction of phosphotyrosine levels of VEGFR-2, PDGFR-β, and KIT, which correlated with tumor growth inhibition.16,17 In a pharmacodynamic analysis of sunitinib in patients with renal cell carcinoma, significantly greater changes in VEGF and sVEGFR-2 and -3 levels occurred in patients experiencing objective responses, compared with those who had SD or disease progression (all P < .05).27 Sunitinib therapy was also associated with increases in soluble VEGF concentrations and decreases in plasma levels of soluble VEGFRs and KIT in this study. sVEGFR-3 may be a novel marker for the biologic activity of sunitinib,27 while sKIT concentrations were correlated with clinical responses. These correlative findings suggest that strategies simultaneously inhibiting both VEGFR and VEGF may be worth exploring.
Pharmacokinetic analysis of systemic exposure to sunitinib demonstrated sufficient serum exposures so as to inhibit sunitinib-targeted tyrosine kinases in preclinical models. Median Ctrough levels of sunitinib (53 to 72 ng/mL) and total drug (sunitinib plus SU12662; 72 to 103 ng/mL) on the last treatment day of cycles 1 to 3 were within the range of The noncontinuous dosing regimen (4 weeks on, 2 weeks off) yielded an almost complete washout of sunitinib Ctrough levels and of SU12662 during the 2-week period before resumption of therapy. Levels of VEGF, sVEGFR-2, and sVEGFR-3 also displayed a cyclical pattern coinciding with the sunitinib dosing schedule. Investigators reported that these biochemical observations were paralleled in several patients with superficial cutaneous or nodal lesions, whose tumors seemed to respond clinically during periods on sunitinib therapy, but then grew during the 2-week period off treatment. These observations have prompted exploration of continuous daily dosing schedules in patients with breast cancer. Phase II studies of a continuous daily regimen in patients with renal cell carcinoma or gastrointestinal stromal tumors have demonstrated efficacy and safety similar to that observed in previous studies using the 4/2 schedule.29,30 We believe these data indicate that sunitinib has activity in advanced breast cancer, and is reasonably well tolerated. These findings are encouraging when compared with other recent experience of single-agent angiogenesis inhibitors in MBC. Overall response rates in similar studies were 9% (confirmed response rate, 7%) with bevacizumab and 2% with sorafenib,31,32 compared with 11% in this study. Median overall survival times in these three trials were 38 weeks for sunitinib, 43 weeks for bevacizumab,31 and 8 weeks for sorafenib.32 In addition, discontinuations due to AEs were lowest in the sunitinib study (0% v 6% for bevacizumab and 6% for sorafenib).31,32 Ongoing trials are evaluating sunitinib in advanced and early-stage breast cancer. These include phase II trials of sunitinib in combination with chemotherapy, and randomized trials comparing chemotherapy/sunitinib combinations against other chemotherapy/angiogenesis inhibitor regimens.
Although all authors completed the disclosure declaration, the following author(s) indicated a financial or other interest that is relevant to the subject matter under consideration in this article. Certain relationships marked with a "U" are those for which no compensation was received; those relationships marked with a "C" were compensated. For a detailed description of the disclosure categories, or for more information about ASCO's conflict of interest policy, please refer to the Author Disclosure Declaration and the Disclosures of Potential Conflicts of Interest section in Information for Contributors. Employment or Leadership Position: Mary Lehman, Pfizer Inc (C); Carlo L. Bello, Pfizer Inc (C); Samuel E. DePrimo, Pfizer Inc (C); Charles M. Baum, Pfizer Inc (C) Consultant or Advisory Role: Anthony D. Elias, Pfizer Inc (C) Stock Ownership: Mary Lehman, Pfizer Inc; Carlo L. Bello, Pfizer Inc; Samuel E. DePrimo, Pfizer Inc; Charles M. Baum, Pfizer Inc Honoraria: Kathy D. Miller, Pfizer Inc Research Funding: Anthony D. Elias, Pfizer Inc; Hope S. Rugo, Pfizer Inc; Antonio C. Wolff, Pfizer Inc; Peter D. Eisenberg, Pfizer Inc; Kathy D. Miller, Pfizer, Inc Expert Testimony: None Other Remuneration: None
Conception and design: Hope S. Rugo, Antonio C. Wolff, Mary Lehman, Carlo L. Bello, Samuel E. DePrimo, Charles M. Baum Financial support: Charles M. Baum Administrative support: Bonne J. Adams, Kathy D. Miller Provision of study materials or patients: Harold J. Burstein, Anthony D. Elias, Hope S. Rugo, Melody A. Cobleigh, Antonio C. Wolff, Peter D. Eisenberg, Charles M. Baum Collection and assembly of data: Harold J. Burstein, Anthony D. Elias, Hope S. Rugo, Peter D. Eisenberg, Mary Lehman, Bonne J. Adams, Samuel E. DePrimo, Charles M. Baum, Kathy D. Miller Data analysis and interpretation: Harold J. Burstein, Anthony D. Elias, Antonio C. Wolff, Mary Lehman, Carlo L. Bello, Samuel E. DePrimo, Charles M. Baum Manuscript writing: Harold J. Burstein, Anthony D. Elias, Peter D. Eisenberg, Mary Lehman, Carlo L. Bello, Samuel E. DePrimo Final approval of manuscript: Harold J. Burstein, Anthony D. Elias, Hope S. Rugo, Melody A. Cobleigh, Antonio C. Wolff, Peter D. Eisenberg, Mary Lehman, Charles M. Baum
We thank medical writers at ACUMED (Tytherington, United Kingdom) for assistance in drafting this manuscript.
published online ahead of print at www.jco.org on March 17, 2008. Authors' disclosures of potential conflicts of interest and author contributions are found at the end of this article.
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Copyright © 2008 by the American Society of Clinical Oncology, Online ISSN: 1527-7755. Print ISSN: 0732-183X
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