SAT-597 A Case of Cribriform Morular Thyroid Carcinoma Leading To a Diagnosis of Familial Adenomatous Polyposis

Abstract J. Qu: None. M. Endo: None. T.S. Tylee: None. Introduction: Cribriform morular thyroid carcinoma (CMTC) is a rare thyroid malignancy strongly associated with familial adenomatous polyposis (FAP). While most cases of CMTC are identified in patients with known FAP, there are sporadic cases of CMTC, and in rare cases CMTC may be the presenting symptom for previously undiagnosed FAP. We present a case of CMTC diagnosed on fine needle aspiration (FNA) of a thyroid nodule with low suspicion ultrasound features that led to a subsequent diagnosis of FAP in a young woman. Clinical Case: A 30-year-old female with no significant past medical history was noted to have a thyroid nodule in 2019. Ultrasound showed a 3.4 x 2.0 x 2.3 cm TR2 left nodule. At the time, FNA was not completed due to low suspicion ultrasound features. In 2022, follow up ultrasound demonstrated no change in size but interval development of macrocalcifications, now classified as TR3. There were no abnormal lymph nodes. FNA was completed with malignant (Bethesda 6) results, concerning for papillary thyroid carcinoma. She underwent total thyroidectomy with left paratracheal node dissection. The pathology results showed a 3.0 cm cribriform morular thyroid carcinoma without angioinvasion, lymphatic invasion, or extrathyroidal extension with negative lymph nodes. While she had no known family history of colon cancer and no gastrointestinal symptoms, she was referred for colonoscopy given the strong association between CMTC and FAP. She was found to have numerous polyps. Endoscopy was subsequently performed, revealing multiple small duodenal polyps and one ampullary adenoma without high grade dysplasia. She completed genetic testing, which showed a pathologic variant in APC and confirmed the diagnosis of FAP. She ultimately received total proctocolectomy with permanent end ileostomy. Conclusion: Cribriform morular thyroid carcinoma is a rare form of thyroid cancer that has high association with FAP. Guidelines recommend yearly thyroid ultrasound screening in those with FAP to identify thyroid nodules and allow for early diagnosis of thyroid cancer. While our patient had a palpable thyroid nodule 2 years prior to diagnosis, it had low suspicion ultrasound features so was not initially biopsied, which delayed her diagnoses of both thyroid cancer and FAP. This case suggests FNA of nodules with low suspicion ultrasound features should be considered in patients with FAP, even if they do not meet current American College of Radiology criteria for FNA. Saturday, June 1, 2024