About Medullary Thyroid Cancer (MTC)
Medullary Thyroid Cancer
Medullary thyroid carcinoma (MTC) is a rare type of thyroid cancer. It accounts for <3% of all thyroid cancers. MTC starts in the thyroid’s C cells. Sometimes it starts by random chance. Other times it can be caused by genes that are inherited. In some patients, we do not know the cause and more research is required to determine the other causes of MTC.
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MTC: Cause, Disease Course, Follow Up and Prognosis
Cause of MTC
Medullary thyroid carcinoma (MTC) is a rare type of thyroid cancer. It accounts for <3% of all thyroid cancers. MTC starts in the thyroid’s C cells. Most of the time it starts by random chance through an alteration in a gene within the C cell of the thyroid, called a somatic mutation. Other times it can be caused by a gene that is inherited. Inherited MTC usually occurs within the Multiple Endocrine Neoplasia Type 2 (MEN2) syndromes. In some patients, we do not know the cause and more research is required to determine the other causes of MTC.
Not every person with MTC can be cured. For people whose cancer couldn’t be completely removed and for people whose cancer came back after surgery, their cancer may stay the same size (remains stable), grow slowly, or grow quickly. Sometimes MTC can grow again in the neck where it started and other times it can grow in other parts of the body (distant metastases). Sometimes cancer that comes back is watched by doctors to see how quickly it grows (called active surveillance), and other times it is treated. Treatment available includes active surveillance, surgery, standard systemic therapy, systemic therapy in a clinical trial, and focal therapy.
Treatment for MTC that has come back after surgery may be different from treatments for other types of cancer that have come back. Sometimes MTC is not treated beyond active surveillance because the cancer is small, stable, or growing slowly for a long time.
Follow up for patients with a history of MTC usually includes regular visits with their clinicians, measurement of tumor markers in the blood and imaging.
Calcitonin and carcinoembryonic antigen (CEA) are two tumor markers for MTC that are measured in the blood. Their uses includes: 1) their absolute amount to help estimate how much disease is present (for example a calcitonin level of >500pg/ml when a person is first diagnosed with MTC suggest that they may have disease that has developed at sites outside of the neck) and 2) their trend over time to help estimate how fast the disease is growing. This trend is described as the doubling time and describes the amount of time it takes for the tumor values to double in amount. A longer doubling time usually means that the disease is growing slower.
Imaging may consist only of an evaluation of the neck such as an ultrasound or CT of that region. Alternatively, if there is concern the disease has spread outside of the neck, additional imaging such as CT or MRI of the chest, abdomen, pelvis and spine may be performed. Sometimes a Gallium-68 Dotatate PET/CT can help identify suspected disease, especially when other imaging does not show evidence of MTC.
Timing of follow up depends on the behavior of the disease; if there is no evidence of disease or it is growing slowly, an annual visit may be appropriate. If the disease is growing more quickly, appointments may be more often.
Staging, although it can be predictive of survival, does not necessarily define how the disease course goes.