Dutasteride in Treating Patients With Prostate Cancer

DISEASE CHARACTERISTICS: * Histologically confirmed prostate cancer, meeting all of the following criteria: * Prostate-specific antigen (PSA) \< 10.0 ng/mL * T1c-T2a disease * Gleason sum of 6 or 7 (secondary pattern 4 only) * Patients with low risk disease must meet the following criteria: * Gleason pattern 3 + 3 * PSA \< 10.0 ng/mL * Clinical T2a disease * Patients with Gleason secondary pattern 4 (i.e., Gleason Pattern 3 + 4) are eligible but must not have a primary pattern 4, PSA \> 10 ng/mL, or clinical T2b disease * Measurable disease on MRI of at least 0.2 cc, based on planimetry volume * Biopsy-proven disease within 2 years of screening visit * No biopsy artifact on MRI scan (minimum 12-week interval between biopsy and baseline MRI) * Eligible for active surveillance according to the criteria set out by the National Institute for Health and Clinical Excellence PATIENT CHARACTERISTICS: * ALT and AST ≤ 2 times the upper limit of normal (ULN) * Alkaline phosphatase ≤ 2 times ULN * Bilirubin ≤ 1.5 times ULN * Estimated glomerular filtration rate (eGFR) ≥ 60 mL/min * Able to swallow and retain oral medication * Able and willing to participate in the study for its duration * Able to read and write (health-outcomes questionnaires are written) * Able to understand instructions related to study procedures and give written informed consent * No history of another malignancy within five years that could affect the diagnosis of prostate cancer * No history or current evidence of drug or alcohol abuse within the last 12 months that might confound the results of the study or pose additional risk to the patient * No known hypersensitivity to any 5α-reductase inhibitor or to any drug chemically related to dutasteride * No contraindication for undergoing gadolinium-enhanced MRI, including any of the following: * Inability to see tumor focus of ≥ 0.2 cc on T2 sequences * Previous allergic reaction to gadolinium * Serum creatinine \> ULN * Incompatible pacemaker * Metal fragments in eyes * Hip replacements that give artifact with prostate/pelvis views * Any artifact or condition that reduces image quality of MRI (e.g., inability to keep still) * No unstable serious co-existing medical condition(s) including, but not limited, to any of the following: * Myocardial infarction, coronary bypass surgery, unstable angina, cardiac arrhythmias, clinically evident congestive heart failure, or cerebrovascular accident within 6 months prior to screening visit * Uncontrolled diabetes * Peptic ulcer disease uncontrolled by medical management PRIOR CONCURRENT THERAPY: * No prior radiotherapy (external-beam or brachytherapy), high-intensity focused ultrasound (HIFU), or photodynamic therapy (PDT) * No prior chemotherapy * At least 3 months since prior and no concurrent prostatic surgery, including TUNA, TURP, TUIP, laser treatment, thermotherapy, balloon dilatation, prosthesis, and ultrasound ablation * No prior oral glucocorticoids * Glucocorticoids, except inhaled or topical, are not permitted within 3 months prior to visit one * No prior GnRH analogues (e.g., leuprolide, goserelin) * No prior or concurrent hormonal treatment (e.g., megestrol, medroxyprogesterone, cyproterone, DES) of prostate cancer * No current and/or prior use of the following medications: * Finasteride (Proscar, Propecia), or dutasteride (GI198745, AVODART) exposure within 12 months prior to study entry * Any other investigational 5α-reductase inhibitors within the past 12 months * Anabolic steroids within the past 6 months * Drugs with antiandrogenic properties within the past 6 months (e.g., spironolactone, flutamide, bicalutamide, cimetidine, ketoconazole, progestational agents) * The use of cimetidine is permitted prior to study entry * The use of topical ketoconazole is permitted prior to and during the study * No participation in another investigational or marketed drug trial within the 30 days prior to the first dose of study drug or anytime during the study period