[Update of pathology in medullary thyroid carcinoma]

Medullary thyroid carcinoma (MTC) is the most common neuroendocrine carcinoma within the thyroid gland, characterized by strong invasiveness, high metastasis and recurrence rates. It is relatively rare among thyroid malignancies. The cytological and histological features of MTC are diverse and disperse, presenting as papillary, follicular, solid, trabecular, and spindle cell patterns. Immunohistochemical staining shows variable expression of calcitonin, carcinoembryonic antigen, and neuroendocrine markers. MTC can be classified into hereditary and sporadic types, with most cases caused by germline or somatic mutations in the RET gene located on chromosome 10. The 5th edition World Health Organization classification of endocrine and neuroendocrine tumors categorizes MTC into low-grade and high-grade based on tumor necrosis, mitotic figures, and Ki-67 proliferation index, highlighting that histological grading and RET gene mutations are independent prognostic predictors. This paper summarizes the recent advances in the pathological diagnosis of MTC, focusing on the key roles of the MTC grading system, molecular characteristics, and genetic screening and counseling in risk stratification for recurrence and targeted therapy.