RATIONALE: Androgens can cause the growth of prostate cancer cells. Luteinizing hormone-releasing hormone agonists may lessen the amount of androgens made by the body. Internal radiation uses radioactive material placed directly into or near a tumor to kill tumor cells. Giving luteinizing hormone-releasing hormone agonist together with an iodine I 125 implant may be an effective treatment for patients with prostate cancer.

PURPOSE: This randomized phase III trial is studying how well giving luteinizing hormone-releasing hormone agonist therapy together with an iodine I 125 implant works with or without additional luteinizing hormone-releasing hormone agonist therapy in treating patients with previously untreated prostate cancer.

OBJECTIVES:

• To evaluate the biochemical progression-free survival (PFS), overall survival, clinical PFS, and disease-free survival of patients with previously untreated intermediate-risk prostate cancer treated with neoadjuvant luteinizing hormone-releasing hormone (LHRH) agonist therapy and permanent iodine I 125 implantation with vs without adjuvant LHRH agonist therapy.
• To determine the non-adaptive interval to salvage therapy in patients treated with these regimens.
• To determine the safety of these regimens in these patients.

OUTLINE: This is a multicenter study. Patients are randomized to 1 of 2 treatment arms.

• Arm I: Patients receive neoadjuvant luteinizing hormone-releasing hormone (LHRH) agonist therapy for up to 3 months and undergo permanent iodine I 125 implantation. Patients then receive adjuvant LHRH agonist therapy for up to 9 months.
• Arm II: Patients receive neoadjuvant LHRH agonist therapy and undergo permanent iodine I 125 implantation as in arm I.

DISEASE CHARACTERISTICS:

• Histologically or cytologically confirmed prostate cancer

  • Previously untreated disease

• Intermediate-risk disease, as defined by the following:

  • Clinical stage < T2c
  • Prostate-specific antigen (PSA) ≤ 20 ng/mL
  • Gleason score < 8

PATIENT CHARACTERISTICS:

• ECOG performance status 0-1
• Life expectancy ≥ 3 months
• Leukocyte count ≥ 3,000/uL
• Hemoglobin ≥ 10.0 g/dL
• Platelet count ≥ 100,000/uL
• Serum creatinine ≤ 2.0 mg/dL
• ALT and AST ≤ 100 IU/L
• No other cancer requiring treatment
• No poorly controlled hypertension (i.e., diastolic blood pressure ≥ 120 mm Hg)
• No severe psychiatric disorders, including schizophrenia or dementia
• No poorly controlled diabetes
• Considered appropriate for study participation, as determined by the Principal Investigator or Clinical Investigator

PRIOR CONCURRENT THERAPY:

• No prior drugs for benign prostatic hyperplasia (other than antiandrogen therapy)
• No prior surgery for prostate cancer
• No concurrent steroid drugs (except for ointment)
• No other concurrent antiandrogen therapy