The influence of intramuscular 4-hydroxyandrostenedione on peripheral aromatisation in breast cancer patients

The influence of the aromatase inhibitor 4-hydroxyandrostenedione (4OHA) given intramuscularly on the peripheral aromatisation of androstenedione into oestrone was investigated in postmenopausal women with breast cancer and compared with the suppression of plasma oestradiol (E2). 7 patients were investigated before and during treatment on day 7, i.e. midway between two weekly injections. After an intravenous injection of [3H] androstenedione and [14C] oestrone, urine was collected for 96 h and the isotope ratio determined in the urinary oestrogen metabolites after isolation with high performance liquid chromatography. At 250 mg, 4OHA inhibited aromatisation to [mean (S.D.)] 15.2 (5)% of baseline (P < 0.002). There was significantly greater inhibition to 8.1 (2.7)% at 4OHA 500 mg (P < 0.01). Plasma E2 was reduced to 41.2 (14.1)% of baseline at 4OHA 250 mg with a further reduction to 32.7 (19.8)% at 500 mg (P < 0.05). These results confirm the dose-response relation previously established with plasma oestrogen measurements alone.