Impact of androgen receptor expression in fluoxymesterone-treated estrogen receptor-positive metastatic breast cancer refractory to contemporary hormonal therapy

The purpose of this study is to evaluate survival outcome in patients with hormone receptor (HR)-positive (+) metastatic breast cancer (MBC) who received fluoxymesterone after disease progression while receiving contemporary hormonal therapy, as well as the association between estrogen receptor (ER)/androgen receptor (AR) status and survival outcome in these patients. We retrospectively identified 103 patients treated with fluoxymesterone for HR + MBC from 2000 to 2014 and with at least one previous hormonal therapy in a metastatic setting. A median of 3 (range 1-10) hormonal therapies (aromatase inhibitors, tamoxifen, and/or fulvestrant) were received before fluoxymesterone; 33 patients discontinued fluoxymesterone before progression because of physician decision or adverse events including toxicity in 14 patients. Of the remaining 70 patients, 2 (3 %) had complete response, 7 (10 %) partial response, and 21 (30 %) stable disease for at least 6 months, yielding a clinical benefit rate of 43 %. The median PFS was 3.9 months (95 % CI 3.2-5.3 months). Multivariate analysis revealed no significant association between PFS and the type or number of prior systemic treatments. All 39 patients who had archived tumor slides available for AR staining had ER + carcinoma; 10 had aeyen1 % but < 10 %, 18 had aeyen10 %, and 11 had no AR nuclear expression. AR positivity with various cutoffs (i.e. any AR + cells, aeyen1 % AR + cells, or aeyen10 % AR + cells) was not significantly associated with survival outcome. Fluoxymesterone can be considered for patients whose ER + MBC progresses on contemporary hormonal therapy, regardless of the level of AR expression.