Familial adenomatous polyposis (FAP) is an autosomal dominant disorder characterized by germline mutations in the adenomatous polyposis coli (APC) gene. This leads to numerous colorectal adenomas and a high risk of colorectal cancer (CRC). Our stem cell-derived colon organoid model revealed that a heterozygous APC mutation is sufficient to induce colorectal cancer formation. We found a link between APC mutation type, organoid maturation and FAP severity. Here, we show that severe germline mutations in hESCs employ diverse mechanisms of carcinogenesis. FAP1-hESCs expressing a truncated 332-amino acid protein exhibited a hyperactivated mTOR pathway, including PTEN inactivation and increased S6K1 and eIF4E activation. This affected oncogenic c-Myc expression and contributed to apoptosis resistance. Rapamycin treatment restored differentiation potential in FAP1 organoids but not FAP2 organoids, which expressed a larger truncated protein without mTOR pathway activation. Our in vitro colon organoids system findings were validated in human patients. Notably, a colon from a FAP1 patient exhibited high expression of mTOR pathway proteins. These findings highlight the potential of rapamycin for personalized therapy in FAP patients with distinct mTOR-mediated APC mutations. Our colon organoid model is valuable for studying CRC and developing new diagnostic, preventive, and therapeutic approaches to prevent or delay tumorigenesis in FAP patients.
© 2025. The Author(s).