There is often no definitive cause of thyroid cancer. However, listed below are a few known risk factors for developing Medullary Thyroid Cancer.

Genetic Factors

Medullary Thyroid Cancer (MTC) can be either sporadic or hereditary. Approximately 80% of cases are sporadic, meaning that there was no family history of MTC. The exact etiology, or cause, of sporadic MTC is not fully understood.

The remaining 20% of cases of MTC are hereditary, meaning that the disease occurs due to genetic mutations that are inherited from family members. These inherited forms of MTC usually occur at a younger age (childhood or early adulthood) and can be categorised as one of 3 main syndromes: Multiple Endocrine Neoplasia 2A (MEN 2A), Multiple Endocrine Neoplasia 2B (MEN 2B), and Familial MTC (FMTC).


Patients MEN 2A tend to have MTC, along with additional growths (parathyroid hyperplasia) or tumours in the parathyroid and adrenal glands. One example is pheochromocytomas, which are rare, hormone-secreting tumors in the adrenal gland that produce epinephrine and norepinephrine, causing symptoms such as sweating and headaches, among others.


Patients MEN 2B tend to have MTC and pheochromocytomas, as well as benign growths of nerve tissue within the oral cavity or elsewhere, called mucosal neuromas.  Medullary thyroid carcinomas related to MEN 2B are often more aggressive.

Familial Medullary Thyroid Cancer

Patients with FMTC present with cancer only in the thyroid and/or associated metastatic lymph nodes. FMTC is not associated with any other tumours or altered hormonal production, as are MEN 2A and MEN 2B.

RET Proto-oncogene Mutations

Genetic mutations in the RET proto-oncogene are known to be the most prevalent risk factor in the development of MTC. These mutations occur in both hereditary and sporadic MTC. If this mutation is detected, screening for other related tumours (such as those present in MEN 2A and MEN 2B) should be performed. The presence of RET proto-oncogene mutations is associated with both an earlier age of presentation and a more aggressive disease.