Atypical Papillary Thyroid Carcinoma with Squamous Metaplasia and RET/NRAS/TERT/PIK3CA Mutations: A Case Report

Background: Papillary thyroid carcinoma (PTC) with squamous metaplasia is a relatively rare and special subtype adenocarcinoma of thyroid which involves multiple genetic changes. We reported a rare case of atypical PTC with squamous metaplasia and RET/NRAS/TERT/PIK3CA mutations which was confirmed after surgical resection pathologically. Case summary: A 2.5×2.5×2 cm3, smooth, hard, clear boundaries and solid nodule on the left thyroid gland was found on relevant physical examination of the patient. And then, the unilateral radical resection of thyroid carcinoma was performed after diagnosing. The tumor cells were squamous metaplasia and arranged in structures with diffuse growth pattern microscopically. At high magnification, stretched nucleus, nuclear grooves and internuclear pseudoinclusions in tumor cells were detected, and the follicular epithelium cells were atypical. Immunohistochemical staining shown strong positiveness of CK19, TTF-1, P40 and Galectin-3, partial positiveness of TG of tumor cells and negativeness of Calcitonin, which could exclude medullary thyroid carcinoma (MTC). Furthermore, first generation sequencing of 18 PTC related genes techniques shown RET, NRAS, TERT and PIK3CA was mutated. Conclusion: Genetic detection is vital to the diagnosis of thyroid adenocarcinoma, especially for the PTC with atypical morphology or rare metaplasia