In addition to the classical papillary, follicular, poorly differentiated, undifferentiated and medullary carcinomas there are a number of rare forms of thyroid carcinoma.
Squamous Cell Carcinoma
Representing about 1% of all thyroid malignancies, SCC of the thyroid behaves in a similar way to undifferentiated thyroid carcinoma and has a poor prognosis.
A low grade malignant lesion that consists of epidermoid cells and mucocytes. It accounts for about 0.5% of thyroid malignancies. There is a variable quantity of extracellular mucin. The mucous cells usually line gland-like structures. Prognosis is similar to the low grade thyroid carcinomas.
There are a number of thymus related malignancies which are all very rare.