This is a Phase I study of the combination tamoxifen and 9-cis-Retinoic acid in patients with breast cancer. The primary objective of the study is; 1) to determine the maximum tolerated dose of 9-cis-Retinoic acid in combination with Tamoxifen and to determine the overall and dose limiting toxicities. Other objectives are: 2) to determine the effect of Tamoxifen on the pharmacokinetics of 9-cis-Retinoic acid; 3) to evaluate the anti-tumor activity of this combination therapy within the context of a phase I study; 4) and to determine the expression of surrogate biomarkers of breast carcinogenesis before and after treatment.