Relugolix in Combination with Radiation Therapy for Treating Patients with High Risk Prostate Cancer

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 or unfavorable intermediate risk cancer with Decipher score > 0.6 * Unfavorable intermediate risk is defined as: ** Two or more intermediate risk features (grade group 2-3, prostate specific antigen [PSA] 10- 20, T2b-T2c) OR ** Grade group 3 OR ** One intermediate risk feature (grade group 2-3, PSA 10-20, T2b- T2c) with >= 50% of cores positive * High risk is defined as: ** T3a or ** Grade group 4 or 5 or ** 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 > 470 ms
• Prior pelvic therapy that would significantly overlap with radiation treatment fields
• Prior prostatectomy