Clinical Research Directory

Inclusion Criteria: * Ability of participant or Legally Authorized Representative (LAR) to understand this study, and participant or LAR willingness to sign a written informed consent * Age ≥ 18 years * Eastern Cooperative Oncology Group (ECOG) performance status 0 - 1 * Life expectancy \> 5 years * Patient diagnosed with National Comprehensive Cancer Network (NCCN) high risk and very high risk prostate cancer. * High risk is defined as: * T3a or * Grade group 4 or 5 or * Prostate-specific antigen (PSA) \> 20 ng/mL * Very high risk is defined as: * T3b to T4 or * Primary Gleason pattern 5 or * Two or three high-risk features or * \> 4 cores with grade group 4 or 5 * Eligible for treatment with combination brachytherapy, external beam radiation, and ADT * Leukocytes \>= 1.0 K/UL * Platelets \>= 100 K/UL * Hemoglobin ≥ 9 g/dL * Aspartate aminotransferase and alanine aminotransferase ≤ 2.5 x upper limit of normal (ULN) * Men with partners of child-bearing potential must agree to practice sexual abstinence or to use the forms of contraception listed for the duration of study participation and for 2 weeks following completion of relugolix therapy Exclusion Criteria: * Simultaneously enrolled in any therapeutic clinical trial * Current or anticipating use of other anti-neoplastic or investigational agents while participating in this study * Diagnosed with a psychiatric illness or is in a social situation that would limit compliance with study requirements * Has a known allergic reaction to any excipient or component contained in the study drug formulation * Active grade 3 (per the National Cancer Institute \[NCI\] CTCAE, version 5.0) or higher viral, bacterial, or fungal infection within 2 weeks prior to the first dose of study treatment * Current androgen deprivation therapy (unless testosterone \> 50 ng/dL). Please note prior or concurrent bicalutamide at 50 mg/daily or less is allowed. Prior androgen deprivation therapy is allowed if testosterone has recovered to \> 50 ng/dL * Prolonged echocardiogram corrected QT (QTc) interval \> 440 ns * Prior pelvic therapy that would significantly overlap with radiation treatment fields * Prior prostatectomy