2525 Background: Many advanced ER+ breast cancer pts show intrinsic resistance to endocrine treatment with the remainder acquiring resistance. Androgenic steroids upstream of aromatase can drive steroid receptor signaling critical to tumour growth. Evidence also exists for an ERα-/AR+ subset of breast cancers transcriptionally similar to ERα+ disease. We hypothesized that AA, a cytochrome (CYP) 17 inhibitor that irreversibly inhibits androgen and estrogen synthesis, would have anti-tumour activity in ER+ or ER-/AR+ pts.
METHODS
Post-menopausal women with ER+ or ER-/AR+ advanced breast cancer resistant to >2 lines of hormone therapies were treated in 6-pt cohorts with AA at doses between 250 and 2000mg daily.
RESULTS
A total of 25 pts were treated in the phase I trial with 2 pts ongoing on study. Median time on treatment was 1.8 mths (range 0.7 - 11.6 mths). There were no dose limiting toxicities. The majority of adverse events (AEs) were Common Toxicity Criteria grade 1 or 2: fatigue, nausea, anorexia, dyspnoea, palpitations, dizziness and flushes. Hypokalemia was frequent, due to secondary mineralocorticoid syndrome: grade 3/4 hypokalemia occurred in 4 pts. This was effectively managed with potassium supplementation, hydrocortisone (20 mg mane, 10 mg nocte) and eplerenone (50-200 mg) with no clinical consequences. Other grade 3 AEs were neutropenia and reduced left ventricular ejection fraction (1 pt) and exercise-induced hypotension with dizziness (1 pt). At the 2000mg dose 5/5 subjects had suppression of estradiol, testosterone, DHEA and DHEAS to below the lower limit of detection of the assay. Two pts (both ER+/AR+) continued on study beyond 11 mths, one of whom achieved a radiological partial response and 80% reduction in serum CA15.3 from baseline. Pharmacokinetic data will be presented.
CONCLUSIONS
AA is well tolerated in advanced breast cancer pts with preliminary evidence of antitumour activity. The predominant AEs are mechanism-based (hypokalemia) and can be managed expectantly, although careful monitoring of potassium levels is recommended.