Phase II study of tamoxifen and high-dose retinyl acetate in patients with advanced breast cancer.

Retinoids have shown a tumor growth inhibition and a synergistic activity with hormonal manipulations in human breast cancer cell lines and rat mammary carcinoma. To investigate the potential usefulness of this synergistic activity in human breast cancer, 33 postmenopausal patients with advanced disease were treated with the combination of tamoxifen (10 mg p.o. three times a day) and retinyl acetate (300,000 IU p.o. daily). Out of 31 evaluable patients, 3 achieved complete response, 9 partial response (overall response rate: 38.5%, 95% confidence interval = 21%-56%) and 16 (52%) showed no change. The median duration of response was 11.5 months (range: 3-19+ months), while the 2-year overall survival rate for the entire group of patients was 63%. Toxicity was generally mild, hot flushes, nausea (and/or vomiting), headache and cutaneous itching being the most frequent side-effects. Only 1 patient discontinued treatment for severe toxicity. These preliminary results suggest that the combination of tamoxifen and high-dose retinyl acetate is a safe and effective regimen for breast cancer patients. However, the study design does not allow us to establish whether the very low rate of early disease progression we observed might be related to a possible synergistic effect between retinoids and antiestrogens or rather to the quite indolent disease of the patients who have been selected for entry into this trial.