Plasma retinol levels and side effects following high-dose retinyl acetate in breast cancer patients.

Plasma retinol levels and toxicity were evaluated in thirteen metastatic breast cancer patients treated orally with high-dose (300,000 I.U./day) retinyl acetate in combination with oral tamoxifen. Following the first dose of the drug, there was a drop of plasma retinol concentrations followed by a recovery to the pre-treatment levels and by a further increase to reach a plateau six to eight hours after drug administration. During the first two months of treatment cumulative increase of plasma retinol was seen, and long-term systemic concentrations in the +50-60% range level were maintained by the treatment. The toxicity observed was acceptable and included gastrointestinal symptoms, skin toxicity and headache. These toxicities could be related to the long-term increase of retinol systemic concentrations. We concluded that the daily dose of 300,000 I.U. retinyl acetate can be administered to cancer patients over a period of several months, is well tolerated and yields a substantial increase of systemic retinol.