High‐grade medullary thyroid carcinoma with papillary‐like nuclear features: A report of five cases

Abstract

AbstractBackgroundMedullary thyroid carcinoma (MTC) with papillary‐like nuclear features has not been previously described. Here, we aimed to describe the unique features of MTC and examine their prognostic value as markers of high‐grade MTC.MethodsOf the 110 MTC patients reviewed, a total of five (4.5%) who exhibited MTC with papillary‐like nuclear features based on observations from cytological preparations were included in this study. Papillary‐like nuclear features were defined as exhibiting all of the following characteristics: ground‐glass chromatin pattern, grooves, indented membrane, and lobulation.ResultsThe patients included four females and one male, with a median age of 70 years. Calcitonin‐doubling times for patients 1 and 3 were 0.8 and 0.34 years, respectively. Cytologically, patients 4 and 5 displayed a Ki‐67 labeling index of 5.1% and necrotic cells, respectively. All three histologically evaluated patients exhibited papillary‐like nuclear features and a Ki‐67 labeling index of >5.0%. Patients 1 and 3 had mitotic counts of ≥5 per 2 mm2. The MTC in all five patients was classified as high‐grade. Moreover, patient 1 harbored a RET mutation (M918T), while RET (R912W), BRAF (V600E), and CTNNB1 (S33F, T41I) mutations were present in patient 2.ConclusionOur work suggests that papillary‐like nuclear features in MTC may be associated with high‐grade tumors. These findings may be cytologically indicative of high‐grade tumors other than necrosis or mitosis.