PAX8 and medullary thyroid gland carcinoma: While TTF-1 is typically expressed in most medullary thyroid carcinomas, one should also note that PAX8 antibodies can show reactivity depending on their clones; for instance, most C-terminus specific PAX8 antibodies and N-terminus-specific MRQ-50 PAX8 antibody are often negative in medullary thyroid carcinomas [39].