Cyclophosphamide and Dexamethasone for the Treatment of Metastatic Castration Resistant Prostate Cancer

Inclusion Criteria

• Ability to understand and willingness to sign an informed consent form
• Ability to adhere to the study visit schedule and other protocol requirements
• Adults >= 18 years of age at time of consent
• Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1 or 2
• Life expectancy >= 3 months
• Histologically or cytologically confirmed prostate adenocarcinoma
• Metastatic status defined as at least 1 documented metastatic lesion on either a bone scan or a computed tomography (computed tomography [CT] / positron emission tomography [PET] / magnetic resonance imaging (MRI) scan
• Must have less than 50 ng/dL testosterone
• Must have demonstrated disease progression after treatment with 2 or more prior lines of therapies for castration resistant prostate cancer (CRPC), including one second generation androgen targeted agent (such as abiraterone or enzalutamide).
• PSA defined progression after most recent directed therapy. Progression is defined as PSA increase >= 25% of baseline or absolute increase of >= 2 ug/L on two PSA measurements at least 7 days apart
• Absolute neutrophil count (ANC) >= 1.0 x 10^9/L
• Platelet count >= 100 x 10^9/L
• Hemoglobin >= 8 g/dL
• Total bilirubin level =< 1.5 x the upper limit of normal (ULN) range
• Aspartate aminotransferase (AST) and alanine transaminase (ALT) levels =< 2.5 × ULN or AST and ALT levels =< 5 x ULN (for participants with documented metastatic disease to the liver)
• International normalized ratio (INR) and activated partial thromboplastin time (aPTT) =< 1.5 x ULN (for participants on anticoagulation they must be receiving a stable dose for at least 1 week prior to first treatment)
• Creatinine clearance > 30 mL/min by Cockcroft-Gault formula
• Participants with BRCA1/2 or homologous recombination (HR) deoxyribonucleic acid (DNA) repair mutations, and/ or microsatellite instability (MSI) must have received prior treatment (e.g., PARP inhibitors or other agents) for BRCA/ HR DNA repair mutation and/ or MSI
• Participants with known active hepatitis B virus (Hep B) are allowed if antiviral therapy for hepatitis B has been given for >8 weeks and viral load is < 100 IU/mL prior to first dose of trial treatment. Participants with treated or untreated hepatitis C virus (HCV) are allowed.
• Male participants who agree to use highly effective method of birth control with their partner (e.g., implants, injectables, birth control pills with two hormones, intrauterine devices [IUDs], complete abstinence or sterilized partner, and female sterilization) and a barrier method (e.g., condoms, vaginal ring, sponge, etc.) during the period of therapy and for 90 days after the last dose of study drug

Exclusion Criteria

• Any condition that would prohibit the understanding or rendering of informed consent
• A history of any other active malignancy with progression and requiring treatment/intervention, with the exception of cutaneous malignancies such as basal cell carcinoma, squamous cell carcinoma, melanoma, or the type of malignancy being studied in this protocol
• Participants with urinary outflow obstruction that has not been treated or managed with either indwelling catheter or self-catheterization
• Severe untreated infection that in the opinion of the investigator would interfere with participant safety or compliance on trial within 28 days prior to enrollment
• Any condition, including concomitant disease, additional malignancies, laboratory abnormalities, or psychiatric illness, that in the opinion of the investigator would interfere with the participant’s safety or compliance while on trial