Medullary thyroid carcinoma (MTC), originating from parafollicular calcitonin-producing C cells, accounts for 5-7% of all thyroid malignancies. Approximately 75% of MTC cases have a sporadic presentation, while the remaining 25% are inherited as an autosomal dominant trait. In the latter, MTC can coexist with other malignancies as part of the hereditary multiple endocrine neoplasia type 2 (MEN2) syndromes MEN2A and MEN2B. MEN2A includes: (i) classical MEN2A, (ii) MEN2A with cutaneous lichen amyloidosis, (iii) MEN2A with Hirschsprung disease (HSCR), and (iv) the familial MTC (FMTC) variant. MTC has high penetrance and is the common manifestation in all these pathologies, being the only clinical manifestation in FMTC. However, assigning a family to the FMTC variant has proven to be challenging. In fact, in some families initially showing only MTC and diagnosed with FTMC, Pheo developed after a long-term follow upfollow-up. Therefore, according to the latest ATA recommendations, FMTC includes families or individuals with only MTC full fillingfulfilling well-defined additional strict criteria at the time of diagnosis (Wells et al., 2015). The other thyroid malignancies arise from the follicular cells and encompass papillary thyroid carcinoma (PTC), which accounts for approximately 85% of the thyroidthyroid cancers, in addition to follicular, poorly differentiated, and the anaplastic thyroid carcinomas. (Fagin and Wells, 2016).