PRIOR CONCURRENT THERAPY: Biologic therapy: Prior monoclonal antibody HER2 therapy for metastatic disease allowed only if combined with chemotherapy or hormonal therapy and treatment failed No concurrent immunotherapy Chemotherapy: See Disease Characteristics At least 4 weeks since prior cytotoxic chemotherapy (at least 6 weeks since prior mitomycin or nitrosourea) No prior retinoid therapy for breast cancer At least 3 months since any other prior retinoid therapy except topical application for dermatological indications No concurrent chemotherapy Endocrine therapy: See Disease Characteristics At least 2 weeks since prior non-FDA approved hormonal therapy No other concurrent hormonal therapy except chronic low dose hormone replacement therapy or low dose corticosteroids for noncancer indication Radiotherapy: See Disease Characteristics Prior radiotherapy allowed Concurrent radiotherapy allowed only to non-indicator tumor(s) that do not represent new disease or disease progression Surgery: Prior surgery allowed Other: At least one month since prior investigational therapy (except hormonal) No other concurrent investigational therapy Concurrent medication with drugs that significantly alter hepatic metabolism (e.g., phenobarbital, phenytoin, oral azole antifungals) allowed only if dosage stable No more than 15,000 IU of vitamin A consumed daily