Endocrine Abstracts

JOINT2177

In the 2022 WHO classification, CMC was removed from the group of papillary carcinomas and included as a thyroid tumour of uncertain histogenesis. This neoplasm accounts for 0. 1-0. 2% of all TCs and was first described in 1994. Almost all CMC have genetic alterations in the Wnt/beta-catenin pathway, with APC mutations being the most common, associated with familial adenomatous polyposis (FAP) or as a sporadic form. We present four women with different clinical presentations. Case 1. Cerebellar medulloblastoma at 11 and colectomy by colectomy at 28 with positive genetics. Sonographic screening showed multinodular goiter with CNB suggestive of PTC. Surgery (2010) at 43 years showed four unencapsulated CMC foci 1. 5-4 mm in diameter, intrathyroidal with IHQ positive for TTF-1 and negative for HBME-1. Treated with I131 and without recurrence after 14 years of F-U. Case 2. Self-detected nodule with CNB suggestive of PTC. Surgery (2012) at 31 showed unifocal, unencapsulated, well-defined 38mm neoplasm with vascular invasion. IHQ positive for TTF-1 and negative for thyroglobulin and HBME-1 except in morules. Negative for mutation in APC and normal colonoscopy. Excellent therapeutic response 12 years after treatment with I131. Case 3. Positive genetic study for APC three years earlier (maternal carrier, c. 1548+1G>T) with subtotal colectomy and immature ovarian teratoma. Self-detected nodule with CNB suggestive of CMC. Surgery (2019) at 32y showed two foci of 20 and 3mm, unencapsulated, without vascular invasion and negative sentinel node (0/7). IHQ positive for TTF-1, beta-catenin and Ck19, negative for thyroglobulin and HBME-1. Treatment with I131 and excellent response five years later. Mesenteric desmoid tumour from 2021. Case 4. Positive genetics for APC (maternal carrier, c. 637C>T) and resected colon polyps seven years earlier. Self-detected nodule with CNB suggesting CMC. Surgery at age 21 (November 2024) revealed seven foci of CMC (12-44 mm). The largest had extensive vascular invasion (nine vessels) and focal extrathyroidal extension. Two of nine LNs with tumour foci in the central compartment. IHQ positive for TTF-1, nuclear and cytoplasmic beta-catenin and Ck19 and negative for thyroglobulin and HBME-1 except in morules, Ki-67: 8% with negative study for mutations in TERT promoter. Defined as an independent entity in the recent WHO classification, CMC shows a wide clinical variability at presentation. Sporadic cases tend to be solitary tumours, whereas CMCs associated with germline APC mutations tend to be multifocal. This neoplasm may present an aggressive histological picture even in young patients, especially in larger tumours.