Enzalutamide and Metformin Hydrochloride in Treating Patients With Hormone-Resistant Prostate Cancer

Inclusion Criteria: * Patients must have histologically or cytologically confirmed prostate cancer with a Gleason score available or interpretable; patients must have prostate cancer deemed to be castration-resistant by one or more of the following criteria (despite androgen deprivation and anti-androgen withdrawal when applicable): * Progression of unidimensionally measurable disease assessed within 28 days prior to initial administration of drug * Progression of evaluable but not measurable disease assessed within 28 days prior to initial administration of drug for PSA evaluation and within 42 days for imaging studies (e.g, bone scans) * NOTE: rising PSA, defined as at least two consecutive rises in PSA to be documented over a reference value (measure 1); the first rising PSA (measure 2) should be taken at least 7 days after the reference value; a third confirmatory PSA measure (2nd beyond the reference level) should be greater than the second measure, and it must be obtained at least 7 days after the 2nd measure; if this is not the case, a fourth PSA is required to be taken and be greater than the second measure; measurable disease is not required * Patients who have measurable disease must have had X-rays, scans or physical examinations used for tumor measurement completed within 28 days prior to initial administration of drug * Patients must have non-measurable disease (such as nuclear medicine bone scans) and non-target lesions (such as PSA level) assessed withi…