Aromatase inhibition in male breast cancer patients: biological and clinical implications.

BACKGROUND: The role of aromatase inhibitors (AIs) and their impact on estradiol (E(2)) levels remain unknown in male breast cancer (MBC) patients. PATIENTS AND METHODS: MBC patients with metastatic disease and those treated with AIs were selected from the breast cancer database of the Centre Antoine-Lacassagne (Nice, France). Sex hormone levels were retrospectively assessed on serum samples from our institutional serum bank.
RESULTS: Fifteen patients entered the study. Two patients (13%) had complete response, four patients (27%) had partial response, two patients (13%) had stable disease and seven patients (47%) had progressive disease. The median progression-free survival and overall survival were 4.4 months [95% confidence interval (CI) 0.1-8.6] and 33 months (95% CI 18.4-47.6), respectively. All assessable patients (n = 6) had E(2) levels less than the lower limit of the assay during AI treatment. Among them, three had partial response, one had stable disease and two had progressive disease. A large increase in follicle-stimulating hormone, luteinizing hormone and E(2) levels was observed in one responding patient at progression.
CONCLUSIONS: AIs are active in MBC patients. This activity is correlated with a significant reduction in E(2) levels. Secondary resistance is in part related to a deleterious feedback loop resulting in a significant increase in substrate for aromatization.