• Male or female and ≥ 55 years of age

• Have provided written informed consent to participate in the study

• Diagnosis of phenotypic classical FAP with disease involvement of the duodenum or the residual colon/rectum/pouch as the primary disease site.

• Genetic diagnosis of FAP with APC gene mutation (Part 2 only).

• Has undergone colectomy or subtotal colectomy

• Spigelman Classification Stage II or higher.

• Investigator/Participant agrees to leave polyps ≤10 mm unresected during endoscopies performed at Screening and while on study

• Have no significant cardiovascular abnormalities at Screening:

∙ Left ventricular ejection fraction \>50% as determined on screening echocardiogram

‣ A QT interval corrected for heart rate using the Fridericia formula (QTcF) \< 450 msec in men and \<470 msec in women.

• Have no significant hematopoietic abnormalities at Screening:

∙ White blood cell count (WBC) ≥ 3,000/mm3 (non-black populations); 2,700/mm3 (black populations)

‣ Platelet count ≥ 120,000/mm3

‣ Hemoglobin ≥ 10.0 g/dL

‣ No history of clinical coagulopathy.

⁃ Have no significant hepatic abnormalities at Screening:

• Total bilirubin ≤ 1.5 X upper limit of normal (ULN) (individuals with Gilbert syndrome may be enrolled)

∙ AST, ALT, ALP ≤ 2.0 X ULN.

⁃ Have no significant renal abnormalities at Screening: serum creatinine ≤ 1.5 times X ULN.

⁃ Female participants who are women of childbearing potential (WOCBP) must have a negative serum pregnancy test at screening and a negative urine pregnancy test within 24 hours before the first dose of study drug. If the urine test is positive or cannot be confirmed negative, a serum pregnancy test will be required and must be negative for the participant to be eligible.

⁃ All participants must be willing to follow the contraceptive guidance in the protocol and must not be lactating or planning to attempt to become pregnant during the study or for a further period of 4 months after the last dose of study drug or impregnate someone during this study or for a further period of 14 weeks after the last dose of study drug (Appendix 1).

⁃ Absence of gross blood in stool at Screening; red blood on toilet paper only is acceptable.

⁃ Participant must be willing to discontinue use of non-steroidal anti-inflammatory agents (NSAIDs) 6 weeks prior to Study Day 1 and remain off NSAIDs throughout the treatment period of the study (use of aspirin ≤ 700 mg week is allowed.)