Background: Familial adenomatous polyposis (FAP) is an autosomal dominant genetic disorder that carries an almost 100% risk of developing colorectal cancer by the age of 40. The genes primarily mutated in FAP are APC and MUTYH, with approximately 70% to 90% of FAP cases involving mutations in the APC gene, some of which may be associated with thyroid cancer. Case: We describe a case of a 30-year-old female patient with a history of papillary thyroid carcinoma who presented with abdominal pain. Gastrointestinal endoscopy revealed multiple polyps in the stomach and colon, along with liver and lung metastases from colon cancer. Further genetic testing revealed a mutation in the APC gene in this patient. Conclusion: Mutations in the APC gene lead to FAP, which subsequently results in colon cancer, and may also contribute to the development of thyroid cancer. Therefore, we recommend that young thyroid cancer patients should carefully inquire about their family history of genetic diseases, while also considering gastrointestinal endoscopy screening and ophthalmic examinations, and even molecular genetic testing. Additionally, when multiple polyps are found in the stomach and colon, the possibility of APC or MUTYH gene mutations should be considered.