This study will investigate the efficacy of Degarelix, a Luteinizing Hormone Releasing Hormone (LHRH) antagonist, to reduce prostate volume prior to permanent seed prostate brachytherapy. There are 2 eligible populations of men, all of whom will have selected brachytherapy as their treatment of choice for their prostate cancer. Either they have an enlarged prostate that requires size reduction to render brachytherapy technically feasible, or they require androgen ablation in conjunction with brachytherapy for optimal tumor control. The hypothesis is that Degarelix will provide > 30% volume reduction by 3 months in > 30% of men.

All men will have a baseline transrectal ultrasound for brachytherapy planning that has demonstrated an enlarged prostate with or without pubic arch obstruction. After signing the informed consent document they will have a loading dose of 240 mg Degarelix and then monthly maintenance dose injections of 80 mg until such time as sufficient prostate reduction has occured (2-3 months) or they complete the 6 months of required androgen ablation for their disease status.

Inclusion Criteria:

• Histologic diagnosis of prostate cancer
• Favorable risk disease (cT1 or T2a, Gleason score (GS) 6, and Prostate Specific Antigen (PSA) < 10 ng/mL)
• Low-tier intermediate risk disease (cT2c,GS=6,and PSA 10-15 ng/mL, OR GS=7 and PSA < 10 ng/mL)
• Intermediate risk disease AND androgen deprivation therapy recommended by the treating physician for oncologic reasons such as (≥ 50% positive biopsy cores,cT2c,PSA 15-20 ng/mL,GS=7)
• Patient requires baseline planning trans-rectal ultrasound for the purposes of prostate brachytherapy, showing prostate volume > 40 mL and pubic arch interference (not required for those requiring androgen ablation for oncologic reasons)

Exclusion Criteria:

• castrate serum testosterone level
• previous or concurrent pelvic radiotherapy
• unable to give written informed consent
• contraindications to permanent seed prostate brachytherapy or to androgen deprivation therapy
• prior treatment for prostate cancer
• prior trans-urethral resection of the prostate
• previous therapy with a 5-α reductase inhibitor, anti-androgen agent, or LHRH agonist
• previous therapy with degarelix