Gefitinib With or Without Tamoxifen in Treating Patients With Tamoxifen-Resistant Metastatic Breast Cancer

DISEASE CHARACTERISTICS: * Histologically confirmed breast cancer * Metastatic disease * Initial clinical benefit from tamoxifen for metastatic disease, defined by 1 of the following: * Stable disease for 24 weeks or longer * Objective tumor response * Documentation of clinical progression on tamoxifen within the past 6 weeks * Hormone receptor status: * Estrogen or progesterone receptor positive on most recently analyzed biopsy PATIENT CHARACTERISTICS: Age * 18 and over Sex * Not specified Menopausal status * Not specified Performance status * ECOG 0-2 Life expectancy * At least 6 months Hematopoietic * Absolute neutrophil count ≥ 1,500/mm\^3 * Platelet count ≥ 100,000/mm\^3 Hepatic * AST ≤ 1.5 times upper limit of normal (ULN) * Bilirubin ≤ 1.5 times ULN Renal * Creatinine ≤ 1.5 times ULN OR * Creatinine clearance ≥ 50 mL/min Pulmonary * No clinically active interstitial lung disease * Patients with asymptomatic chronic stable radiographic changes are eligible Other * Not pregnant or nursing * Fertile patients must use effective contraception * No known hypersensitivity to gefitinib * No other malignancy within the past 5 years except basal cell carcinoma or carcinoma in situ of the cervix PRIOR CONCURRENT THERAPY: Biologic therapy * No concurrent trastuzumab (Herceptin®) Chemotherapy * No concurrent cytotoxic chemotherapy Endocrine therapy * See Disease Characteristics * At least 2 weeks since other prior tamoxifen * No concurrent hormone replacement therapy * No other concurrent antiestrogens, including raloxifene * No concurrent aromatase inhibitors * No concurrent megestrol * Concurrent systemic steroids for reasons other than skin toxicity allowed provided the steroids were initiated before study entry AND dose remains stable Radiotherapy * Concurrent palliative radiotherapy as short-term treatment for symptomatic bone metastases allowed provided other evaluable sites of disease are present AND treatment lasts no more than 14 days Surgery * Recovered from prior oncologic or other major surgery * No concurrent surgery during and for 7 days after study treatment * No concurrent ophthalmic surgery Other * Recovered from all prior therapy (except alopecia) * More than 30 days since prior investigational drugs * No other concurrent investigational agents * No concurrent administration of any of the following: * Phenytoin * Carbamazepine * Barbiturates * Rifampin * Phenobarbital * Hypericum perforatum (St. John's wort) * Systemic retinoids * CYP3A4 inhibitors (e.g., itraconazole) * Drugs that cause significant sustained elevation in gastric pH ≥ 5