Genetic and Molecular Mechanisms in Assessing Response in Patients With Prostate Cancer Receiving Enzalutamide Therapy

PRIMARY OBJECTIVE: I. To assess the correlations between baseline molecular features and pathways and prostate-specific antigen (PSA) change (\</\>= 50% decline) at 12 weeks versus (vs.) baseline. SECONDARY OBJECTIVES: I. To measure PSA change at 12 weeks and at each study visit vs. baseline after enzalutamide treatment. II. To measure objective response after enzalutamide treatment. III. To assess the correlations between the baseline molecular features and pathways and progression-free survival, disease-specific survival, and overall survival. IV. To assess the correlations between the baseline molecular features and pathways and time to PSA progression. V. To identify molecular features and cellular pathways present in tumors from men with metastatic castrate-resistant prostate cancer (CRPC) that are progressing despite enzalutamide treatment. VI. To explore correlation between baseline molecular features and pathways and changes in circulating tumor cells (CTCs) counts. VII. To explore correlation between baseline molecular features and pathways and objective response. VIII. To assess the correlations between the baseline molecular features and pathways and degree of PSA decline at 12 weeks and maximal PSA decline observed while on study. IX. To assess the correlations between the baseline molecular features and time on treatment. EXPLORATORY OBJECTIVES: I. To assess correlations between cell-free deoxyribonucleic acid (DNA) (cfDNA) molecular features from blood and molecular features and pathways from the biopsy samples. II. To assess correlations between cfDNA molecular features and endpoints in the primary and secondary objectives listed above. III. To assess correlations between cell-free DNA and tumor molecular features and changes in PSA after discontinuing enzalutamide. IV. To explore correlations with baseline molecular features and tissue histology. V. To explore correlations with baseline tissue histology and PSA change, time to PSA progression, time on treatment, progression-free survival, and overall survival. OUTLINE: Patients receive enzalutamide orally (PO) once daily (QD) in the absence of disease progression or unacceptable toxicity. Patients undergo a tumor biopsy of a metastatic site at study entry (prior to initiation of enzalutamide) and after the time of progression. Patients may continue treatment beyond progression at the investigator's discretion. After completion of study treatment, patients are followed up at 2-3 or 6 weeks and then every 12 weeks thereafter.