Inclusion Criteria:
1. Male or female participants aged 18 years or older at the time of informed consent.
2. Ability to understand and willingness to sign a written informed consent document, prior to undertaking any study-related procedures.
3. Confirmed Familial Adenomatous Polyposis (FAP) by molecular genetic testing and at least six polyps of 5-9 mm. Patients with FAP that present thyroid nodule and/ or desmoid tumors are eligible.
4. History of prophylactic colectomy with either ileo-rectal anastomosis (IRA) or ileal pouch-anal anastomosis (IPAA), performed at least 12 months prior to screening, and without ongoing surgical complications.
5. Presence of rectal/pouch polyps at baseline; polyps must be \<10 mm in size. If polyps ≥10 mm are identified during the baseline colonoscopy, they must be endoscopically removed at the time of the baseline colonoscopy before first dose of ST316.
6. Willingness to forgo concurrent use of supplements containing, turmeric, omega-3 fatty acids, oral corticosteroids, NSAIDs, or other FAP-directed drug therapy for the duration of the study. Low-dose aspirin (80-100 mg daily) for cardioprotective indications will be permitted.
7. Adequate organ function as defined by ALL of the following laboratory criteria (obtained within 28 days prior to first dose):
Total bilirubin ≤1.5 × institutional ULN (unless Gilbert's syndrome). Alkaline phosphatase ≤1.5 × institutional ULN. AST (SGOT) ≤1.5 × institutional ULN. ALT (SGPT) ≤1.5 × institutional ULN. Serum creatinine ≤1.5 × institutional ULN.
8. Women of childbearing potential (WOCBP) and male participants who are sexually active with WOCBP must agree to use highly effective contraception from screening throughout study duration and for at least 90 days after last dose.
9. Not currently breastfeeding. Women must agree not to breastfeed from first dose through 90 days after last dose.
Exclusion Criteria:
1. Use of any other investigational agent or participation in an interventional clinical trial within 12 weeks prior to first dose of ST316.
2. Receipt of systemic oral corticosteroids within 30 days prior to first dose of ST316.
3. Uncontrolled intercurrent illness or recent (within 4 weeks) major surgical procedure (excluding disease-related surgery, which should be \>12 months from screening) that would limit compliance or pose undue risk to the participant.
4. History of invasive malignancy within 3 years prior to screening (exceptions: carcinoma of the cervix in situ, carcinoma in situ of any site, or basal/squamous cell carcinoma of the skin that has been completely excised).
5. Concurrent use of anticoagulants with a risk of bleeding that may preclude study-related procedures (i.e., endoscopy and biopsies).
6. Use of other NSAIDs (e.g., ibuprofen) exceeding 4 days per month, within 6 weeks prior to first dose of ST316.
7. Regular use of aspirin at doses exceeding 700 mg per week.
8. Treatment with other FAP-directed drug therapy (including sulindac, celecoxib, or fish oil) within 4 weeks prior to first dose of ST316.
9. Any of the following findings on baseline biopsy obtained during screening colonoscopy:
1. Colorectal cancer on biopsy.
2. Duodenal cancer on biopsy.
3. High-grade dysplasia found on polyp biopsy where the polyp has not been completely removed.
4. A large polyp (\>1 cm) not completely removed at baseline colonoscopy.
10. QTcF \>480 ms before first dose of ST316.
11. Significant medical or psychiatric disorder that would preclude study participation or informed consent capacity.
12. Known hypersensitivity to ST316 or any of its excipients.
13. Currently pregnant, breastfeeding, or planning to conceive during the projected duration of the study (including 90 days post-last dose).
