trans-4-Hydroxytamoxifen concentration and metabolism after local percutaneous administration to human breast.

trans-4-Hydroxytamoxifen (4-OHTAM), a very active metabolite of the antiestrogen tamoxifen, was percutaneously administered to the affected breast of nine patients before surgery for breast cancer in order to evaluate 4-OHTAM absorption through the skin and its subcellular localization and metabolism. After percutaneous administration of 80 muCi, [3H]-4-OHTAM was detected in breast tissue. It was especially concentrated in tumor tissue and nuclear and cytosolic fractions, in which it remained unmetabolized except for limited isomerization from the trans to the cis form. In contrast to breast tissue, concentrations of radioactivity remained low in plasma but with a high proportion of metabolites. In another experiment [3H]tamoxifen was percutaneously administered over the breast of 3 patients, resulting in tissue retention weaker and shorter than after [3H]-4-OHTAM. In addition [3H]-4-OHTAM was administered to either breast or abdominal skin; the appearance of radioactivity in plasma and urine was delayed after administration to the breast in comparison with administration to the abdomen. It therefore appears that 4-OHTAM passes through the skin and is concentrated in receptor structures of breast tissue, thus avoiding the hepatic metabolism subsequent to p.o. administration. We suggest that local percutaneous administration of this active antiestrogen could be useful in the treatment of hormone-dependent benign breast diseases.