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Authors' Affiliations: Breast Cancer Medicine Service, Departments of Pathology, Biostatistics, and Radiology, Memorial Sloan-Kettering Cancer Center; Weill Medical College of Cornell University, New York; Dana-Farber Cancer Institute; Massachusetts General Hospital, Boston, Massachusetts; Mayo Clinic, Rochester, Minnesota; Georgetown Lombardi Comprehensive Cancer Center, Washington, District of Columbia; University of North Carolina at Chapel Hill, Chapel Hill; Duke University Medical Center, Durham, North Carolina; University of California, San Francisco Helen Diller Family Comprehensive Cancer Center, UCSF, San Francisco, California; University of Alabama at Birmingham, Birmingham, Alabama; and The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins University, Baltimore, Maryland.
Published: October 2013
AI Article Synopsis
Article Abstract
Purpose: Patients with hormone receptor-negative breast cancer generally do not benefit from endocrine-targeted therapies. However, a subset with androgen receptor (AR) expression is predicted to respond to antiandrogen therapies. This phase II study explored bicalutamide in AR-positive, estrogen receptor (ER), and progesterone receptor (PgR)-negative metastatic breast cancer.
Experimental Design: Tumors from patients with ER/PgR-negative advanced breast cancer were tested centrally for AR [immunohistochemistry (IHC) > 10% nuclear staining considered positive]. If either the primary or a metastatic site was positive, patients were eligible to receive the AR antagonist bicalutamide at a dose of 150 mg daily. Clinical benefit rate (CBR), the primary endpoint, was defined as the total number of patients who show a complete response (CR), partial response (PR), or stable disease (SD) > 6 months; secondary endpoints included progression-free survival (PFS) and toxicity. Correlative studies included measurement of circulating endocrine markers and IHC surrogates for basal-like breast cancer.
Results: Of 424 patients with ER/PgR-negative breast cancer, 12% tested AR-positive. The 6-month CBR was 19% [95% confidence interval (CI), 7%-39%] for bicalutamide. The median PFS was 12 weeks (95% CI, 11-22 weeks). Bicalutamide was well-tolerated with no grade 4/5 treatment-related adverse events observed.
Conclusion: AR was expressed in 12% of patients with ER/PgR-negative breast cancer screened for this trial. The CBR of 19% observed with bicalutamide shows proof of principle for the efficacy of minimally toxic androgen blockade in a select group of patients with ER/PgR-negative, AR-positive breast cancer.
