Purpose: To determine the predictive value of androgen receptor (AR) levels in primary tumors of women who undergo medroxyprogesterone acetate (MPA) therapy for advanced breast cancer after relapse on tamoxifen adjuvant therapy.
Methods: Between 1984 and 1987 at Flinders Medical Centre, South Australia, 136 postmenopausal women received adjuvant tamoxifen therapy for lymph node-positive breast cancer. Estrogen receptor (ER), progesterone receptor (PgR), and AR levels, tumor size, and degree of axillary node involvement were determined at the time of diagnosis. The median follow-up period was 81 months; 89 women developed metastatic disease, 83 of whom subsequently received MPA (500 mg/d). The objective response rate ([RR] ie, complete response [CR] and partial response [PR]) and progression-free interval (PFI) were assessed in response to MPA therapy. Associations between RR, PFI, and primary tumor characteristics including ER, PgR, and AR levels were examined using the Mann-Whitney U test, Kaplan-Meier product-limit estimator, and Cox proportional hazards regression, as appropriate.
Results: Thirty-two of 83 patients (38.6%) responded to MPA. RR was significantly associated with the presence of AR (P < .001), but not with other primary tumor characteristics or duration of tamoxifen therapy. After initiation of MPA treatment, PFI increased with increasing concentration of AR in the primary tumor.
Conclusion: Response to MPA after adjuvant tamoxifen treatment for lymph node-positive breast cancer was positively associated with AR level in the primary tumor. This finding suggests that MPA action in breast cancer may be mediated in part by the AR.