RATIONALE: Some drugs used in chemotherapy can reduce the pain experienced by some people with cancer. Combining more than one drug may be more effective at reducing cancer pain. It is not known whether receiving combination chemotherapy with clodronate is more effective than receiving combination chemotherapy without clodronate for hormone refractory metastatic prostate cancer.

PURPOSE: Randomized double-blinded phase III trial to compare the effectiveness of combination chemotherapy using mitoxantrone plus prednisone with or without clodronate in treating pain in patients with hormone refractory metastatic prostate cancer.

OBJECTIVES: I. Compare the effect of mitoxantrone and prednisone with or without clodronate on localized bone pain in patients with hormone refractory metastatic prostate cancer. II. Compare the overall survival and quality of life of these patients after these treatments.

OUTLINE: This is a randomized, double blinded, placebo controlled, multicenter study. Patients are stratified according to quality of pain (mild vs moderate) and previous corticosteroids or one regimen of non-anthracycline-containing cytotoxic chemotherapy (e.g., estramustine) vs none. Patients are assigned to 1 of 2 treatment arms. Arm I consists of oral prednisone twice a day and intravenous mitoxantrone followed by intravenous clodronate administered over 3 hours every 3 weeks. Arm II consists of oral prednisone twice a day and intravenous mitoxantrone followed by intravenous placebo administered over 3 hours every 3 weeks. Doses are adjusted for myelosuppression. Treatment continues until disease progression (although patients initially on placebo can continue on open-label clodronate) or until the maximum cumulative dose of mitoxantrone is reached. Patients with a palliative response may continue on prednisone and the study drug (clodronate or placebo) until disease progression. Quality of life is assessed before and every 3 weeks during study treatment. A daily pain diary is also maintained. All patients are followed at 2 weeks and then every 3 months until death.

PROJECTED ACCRUAL: This study will accrue 204 patients.

DISEASE CHARACTERISTICS: Histologically confirmed adenocarcinoma of the prostate or metastatic carcinoma of presumptive prostate origin as manifest by the presence of sclerotic bony metastases and a serum PSA level greater than the upper limit of normal Radiologically proven progressive bone disease (e.g., new bone scan lesions, increased uptake of isotope at previous sites of disease, and/or increasing bone pain) Hormone refractory disease (i.e., disease progression or recurrence despite documented castrate levels of serum testosterone achieved by bilateral orchiectomy or antiandrogen therapy) Bone pain due to metastatic disease Patients must have achieved stable analgesia for at least 7 days No uncontrolled epidural metastases

PATIENT CHARACTERISTICS: Age: Any age Performance status: ECOG 0-3 Life expectancy: At least 3 months Hematopoietic: WBC at least 3,000/mm3 Absolute granulocyte count greater than 1,500/mm3 Platelet count greater than 100,000/mm3 Hepatic: Bilirubin no greater than 3.15 mg/dL Renal: Creatinine less than 2.26 mg/dL Serum calcium no greater than 3.1 mmol/L Cardiovascular: Patients with history of angina pectoris, previous cardiac infarction, hypertension, or valvular or congenital heart disease must have baseline measurement of LVEF exceeding 50% Other: No other malignancy within 5 years except nonmelanomatous skin cancer No active infection or any other contraindication to chemotherapy with mitoxantrone No spinal cord or nerve root compression No unstabilized impending pathological fractures

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: One previous course of chemotherapy allowed No prior mitoxantrone or other anthracycline Endocrine therapy: See Disease Characteristics At least 4 weeks since prior nonsteroidal antiandrogens Radiotherapy: At least 4 weeks since prior radiotherapy At least 8 weeks since prior strontium-89 or samarium-153 Surgery: Not specified Other: No prior bisphosphonate therapy