Mixed Medullary and Papillary Thyroid Carcinoma in a Patient on Tirzepatide.

Medullary thyroid cancer (MTC) stems from thyroid parafollicular C cells and is considered a rare type of neuroendocrine tumor. It can be inherited as part of syndromes, such as familial medullary thyroid cancer (FMTC) and multiple endocrine neoplasia type 2 (MEN 2), or it can arise sporadically. GLP-1 receptor agonist drugs (GLP1 RA), like semaglutide and tirzepatide, carry an FDA black box warning against using them in patients who have a prior history or a family history of MTC or MEN2. This recommendation stems from rodent studies showing thyroid C-cell tumors. Current studies have not confirmed an association between GLP1RAs and risk of differentiated thyroid cancer in human studies. In addition, there is no consensus on screening or evaluating patients for thyroid cancer prior to or during treatment with GLP1 RA. Here, we report a case of mixed medullary and papillary thyroid carcinoma newly diagnosed in a 68-year-old female on tirzepatide for type 2 diabetes who presented with a neck mass.