ZD 1839 in Treating Patients With Prostate Cancer That Has Not Responded to Hormone Therapy

DISEASE CHARACTERISTICS: * Histologically or cytologically confirmed adenocarcinoma of the prostate * PSA at least 20 ng/mL at study entry * Must have documented evidence of disease progression, defined by 1 of the following conditions: * Rising PSA documented after discontinuation of peripheral antiandrogens * Minimum evidence of progression is a 25% increase in PSA over the reference value, provided that the increase is at least 5 ng/mL * Must have a first increase in PSA documented at least 1 week after the reference value and a second increase in PSA documented at least 1 week after the first increase * Progressive measurable disease during androgen ablative therapy (including medical or surgical castration) * Castrate level (no greater than 50 ng/mL) of testosterone required if receiving medical androgen-ablative therapy at study entry * Concurrent luteinizing hormone-releasing hormone agonist therapy required if receiving this medication at study entry PATIENT CHARACTERISTICS: Age: * 16 and over Performance status: * ECOG 0-1 Life expectancy: * Not specified Hematopoietic: * Absolute granulocyte count at least 1,500/mm3 * Platelet count at least 100,000/mm3 Hepatic: * Bilirubin no greater than 2 times upper limit of normal (ULN) * AST/ALT no greater than 2.5 times ULN (5 times ULN if documented liver metastases) Renal: * Creatinine no greater than 2 times ULN Other: * No other malignancy within the past 5 years * No active uncontrolled bacterial, fungal, or viral infection * No significant neurological disorder that would preclude informed consent * No other serious illness or medical condition that would preclude study PRIOR CONCURRENT THERAPY: Biologic therapy: * Concurrent epoetin alfa allowed Chemotherapy: * No prior chemotherapy * No concurrent cytotoxic therapy Endocrine therapy: * See Disease Characteristics * At least 4 weeks since prior peripheral antiandrogens (6 weeks for bicalutamide) * Concurrent steroids allowed if on stable dose for at least 4 weeks before study and no dose increase planned Radiotherapy: * At least 4 weeks since prior radiotherapy except low-dose, nonmyelosuppressive radiotherapy approved by the National Cancer Institute of Canada, Clinical Trials Group Surgery: * See Disease Characteristics * No concurrent ophthalmic surgery Other: * No prior investigational agents * No other concurrent investigational therapy * No concurrent ketoconazole * No concurrent high-dose narcotic therapy for pain (e.g., morphine equivalent dose more than 60 mg/day) * Concurrent bisphosphonates allowed