MTC is a malignant tumor of parafollicular (follicular) cell origin in the thyroid gland. The incidence is 2% to 3%, divided into sporadic and familial. sporadic accounts for about 70% of all medullary carcinomas, preferably in the 50-60 age group, familial has a younger age of onset, accounting for about 30%, and is an autosomal dominant disease. men II, including IIA, IIB and familial medullary carcinomas, currently, familial medullary carcinomas are considered to be the spectrum of disease of MEN IIA.
Serum calcitonin levels correlate with tumor load, but are also non-secretory in <1% of cases. Examination of serum CEA is an important indicator in the follow-up of medullary carcinoma, especially when calcitonin levels are low.
The microscopic morphology of MTC is diverse and can resemble any thyroid malignancy, with typical structures being solid, lobulated, tubular or insular. The tumor cells are highly variable in size and can be round, polygonal, plasma cell-like, or spindle-shaped. The nuclei are low-moderate heterogeneous and have relatively low nuclear fission activity.
Subtypes: There are different types based on cellular and structural features, papillary/pseudopapillary, follicular (tubular/glandular), spindle cell, giant cell, clear cell, eosinophilic, melanotic, squamous subtype, paraganglioma-like, angiosarcoma-like, small cell, and intraperitoneal medullary thyroid carcinoma.
Immunohistochemical indicators: calcitonin, neuroendocrine markers (CD56, synaptophysin, chromogranin A), TTF-1, PAX8 and CEA can be expressed; TG is not expressed.