Medullary thyroid cancer has its origin in the parafollicular cells, which produce calcitonin. These cells are located adjacent to the thyroid's follicules, and are also known as C cells. Medullary thyroid cancer is marked by an increase calcitonin in the blood, as well as by the carcinoembryonic antigen (CEA).

Around 25% of medullary thyroid cancer occurs in families ("hereditary"), with the other 75% being classified as "sporadic." Sporadic medullary thyroid cancer patients tend to be older, and by the time there is a clinical presentation the condition may be more extensive.

Medullary thyroid cancer sufferers' main symptom is diarrhea. Some individuals may also undergo flushing. These symptoms both are especially particular with metastases in the liver, and may be the initial noticed presentation.

If detected early, surgery is a possibility for treatment. Still, there is a risk for recurrence. Unlike many other thyroid cancers, radioiodine treatment is not used against medullary thyroid cancer. External beam radiotherapy may be used with patients at risk for regional recurrence of the cancer, even if the best surgical treatment has already been performed.

Prognosis for medullary thyroid cancer patients where there is metastasis past the thyroid gland is generally poor compared to follicular and papillary cases. Generally, survival rate is better for individuals whose calcitonin levels only slowly increase, or even decrease. Quick increases in calcitonin levels, especially doubling within 6 months, is associated with a lower survival rate.

Other thyroid cancers include:

Anaplastic cancer

Follicular cancer

Lymphoma

Papillary cancer

Additionally, there are non-cancerous thyroid adenoma tumors.