Medullary thyroid cancer, also called medullary thyroid carcinoma (MTC), is one of the least common types of thyroid cancer. There are 4 forms (or types) of medullary thyroid cancer: sporadic, MEN 2A-associated, MEN 2B-associated, and familial. This article will go over the 4 forms of medullary thyroid cancer, giving the basics of each type.