Decreasing Dosing Regimens of Abiraterone 500 mg in Men With Prostate Cancer to Find Lowest Recommended Dose.

Doctors leading this study plan to collect new information about the lowest effective dose of abiraterone acetate in study participants with prostate cancer who are taking abiraterone in combination with prednisone for the first time. The duration of this study will be about 3 months (12 weeks). How long you stay on abiraterone, and at what dose after completion of the 12 weeks of study drug administration, will be up to you and your treating physician.

Doctors leading this study plan to collect new information about the lowest effective dose of abiraterone acetate in study participants with prostate cancer who are taking abiraterone in combination with prednisone for the first time. The duration of this study will be about 3 months (12 weeks). How long you stay on abiraterone, and at what dose after completion of the 12 weeks of study drug administration, will be up to you and your treating physician.

Therefore, this study will evaluate if alternative dosing strategies with 500 mg pills may be equally effective as taking abiraterone 1000 mg daily. This study will specifically assess whether taking 500 mg of abiraterone every other day with a low-fat meal, or 500 mg with a low-fat meal at less frequent intervals (fewer times per week), is equally effective in treating prostate cancer as the 1000 mg/day dose.

Eligibility Criteria:
Inclusion Criteria:

* Histologically or cytologically confirmed prostate cancer with plans to initiate abiraterone acetate
* Have never received prior abiraterone or other androgen receptor modulators, including enzalutamide, apalutamide, or darolutamide.
* Must have a baseline DHEA-S level of \>20 mg/dL (in order to adequately assess DHEA-S response)
* A minimum washout of 28 days for any other anticancer therapy other than medical or surgical castration, prior to first dose of study drug is required.
* Any other radiotherapy or radionuclide require 28-day washout prior to first dose of study drug.
* Denosumab or zoledronic acid are allowed.
* Eastern Cooperative Oncology Group performance status ≤ 2 (Appendix A).
* Participants must have normal hepatic function as defined by clinical lab values set by the study doctor/research team.
* Ability to understand and the willingness to sign a written informed consent document.

Exclusion Criteria:

* Therapy with other hormonal therapy, including any dose of megestrol acetate (Megace), finasteride (Proscar), dutasteride (Avodart), or any herbal product known to decrease Prostate-Specific Antigen levels or any systemic corticosteroid (other than prednisone ≤10mg/day) within 4 weeks prior to first dose of study drug.
* Inability to swallow capsules or known gastrointestinal malabsorption.
* Blood pressure that is not controlled despite \> 2 oral agents (SBP \>160 and DBP \>90 documented during the screening period with no subsequent blood pressure readings \<160/100).
* Serum K+ \< 3.5 mmoL/L. Patients with a K+ \< 3.5 mmoL/L are required to have a documented subsequent K+ \>3.5 prior to enrollment to be eligible.
* Serious intercurrent infections or non-malignant medical illnesses that are uncontrolled.
* Active psychiatric illness/social situations that would limit compliance with protocol requirements.
* Serious heart issues/congestive heart failure as assessed by New York Heart Association's definition of class II, class III, or IV congestive heart failure.
* Taking other medications or drugs with strong inhibitors or inducers of CYP3A4 (See Section 8.12 below for list of strong inhibitor or inducers) due to concerning possible drug-drug interactions with abiraterone.