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

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.