Understanding the Interaction between Androgen Receptor Signaling and Prostate-Specific Membrane Antigen Expression

The goal of this research study is to determine whether hormonal therapies used early in the
course of prostate cancer could increase the amount of Prostate-Specific Membrane Antigen
(PSMA) as detected by PET/CT scans for participants with recurrent prostate cancer. This
study will measure PSMA levels using standard PET/CT scans and participants will receive
standard-of-care androgen receptor antagonist monotherapy.

The names of the treatment interventions involved in this study are:

- Androgen receptor antagonist monotherapy.

- PSMA PET/CT scan

It is expected that about 15 people will take part in this research study.

Participation in this research study is expected to last about 4 weeks.

Inclusion Criteria:

- Patients age 40 or higher with prostate cancer that has been previously treated with
primary definitive local therapies (prostatectomy with or without salvage radiation,
or primary prostate radiation) and subsequently experiencing rising PSA meeting
criteria for biochemical failure (PSA >0.2 ng/dL x2 following prostatectomy, or PSA >
2 + nadir value following primary radiation).

- PSMA PET/CT (Ga68, piflutolastat F-18, or other FDA-approved tracer) during time of
biochemical recurrence, and within 6 weeks of registration, showing at least one
lesion suspicious for recurrent prostate cancer based on size and/or SUV.

- Testosterone >100 ng/dL within 6 months prior to enrollment with no intervening
hormonal therapies.

- Assigned by treating physician to receive standard-of-care AR antagonist monotherapy,
using FDA-approved apalutamide, darolutamide, or enzalutamide.

Exclusion Criteria:

- High disease burden, significant symptoms of disease, or other clinical situation
requiring medical/surgical castration and/or docetaxel during the time of the study.

- Not suitable for AR antagonist therapy (e.g. inability to swallow pills, poor
adherence, advanced liver disease, prohibitive co-payment without available patient
assistance funding, contraindicated drug-drug interaction).

- Older-generation AR antagonists (e.g. bicalutamide) are not allowed on study.