Inclusion Criteria

DISEASE CHARACTERISTICS: Histologically confirmed metastatic breast cancer No CNS
metastases No rapidly progressing visceral disease Previously irradiated lesions(s) may be
designated as measurable indicator tumor(s) only if more than 6 months since radiotherapy,
patient has no other measurable disease regrowth, and bidimensionally measurable regrowth
is documented within 2 months prior to study Stratum 1 (hormonal): Must be hormone
receptor positive (ER or PR) Prior hormonal therapy only allowed for metastatic disease
Must have progressed on last hormonal regimen Must have at least one bidimensionally
measurable tumor Stratum 2 (chemotherapy): Hormone receptor positive or negative Must have
progressed on or after prior chemotherapy (1-2 regimens) for metastatic disease (bone
marrow transplant counts as 2 regimens) Prior hormonal therapy allowed Must have at least
one bidimensionally measurable tumor Stratum 3 (tamoxifen): Must be hormone receptor
positive (ER or PR) and progressing on tamoxifen No symptomatic visceral metastasis if on
adjuvant tamoxifen at time of systemic recurrence Must have at least one bidimensionally
measurable tumor, or lytic bone lesion which measures at least one cm in diameter Hormone
receptor status: See above

PATIENT CHARACTERISTICS: Age: Over 18 Menopausal status: Not specified Performance status:
ECOG 0-2 OR Karnofsky 60-100% Life expectancy: At least 3 months Hematopoietic: WBC at
least 3,000/mm3 Absolute neutrophil count at least 1,500/mm3 Platelet count at least
100,000/mm3 Fasting triglycerides within normal range Hepatic: Bilirubin no greater than
1.5 times upper limit of normal (ULN) SGOT and/or SGPT no greater than 2.5 times ULN
Concurrent medication with drugs that significantly alter hepatic metabolism (e.g.,
phenobarbital, phenytoin, oral azole antifungals) allowed only if dosage stable Renal:
Creatinine less than 2 times ULN OR Creatinine clearance greater than 40 mL/min Concurrent
medication with drugs that significantly alter renal metabolism (e.g., probenecid) allowed
only if dosage stable Other: At least 5 years since any other prior invasive malignancy
except basal cell and squamous cell carcinoma of the skin No serious concurrent illness
that would prevent compliance No history of or clinically significant risk factors for
developing pancreatitis Fasting triglycerides within normal range Not pregnant or nursing
Fertile patients must use effective contraception

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