Medullary Thyroid Carcinoma (MTC)


Medullary thyroid cancer (MTC) is a type of thyroid cancer that affects specialized cells in the thyroid gland called the parafollicular C cells, which are responsible for making calcitonin hormone.1 Calcitonin plays a role in regulating calcium and phosphate levels in the blood.2

Medullary thyroid cancer can either be familial and associated with mutations in the RET proto-oncogene or sporadic.3 

In the US, thyroid cancer in general represents approximately 2% of all cancer types and medullary thyroid cancer represents 2% to 3% of all thyroid cancers.4

Medullary thyroid cancer can spread to the cervical lymph nodes and other parts of the body including the bones, lungs, liver, and brain.4

5-Year Survival Rate of Medullary Thyroid Cancer

The 5-year survival rate is an estimate of the percentage of people with the same type and stage of cancer that are still alive after 5 years of diagnosis.5

According to the American Cancer Society, the 5-year survival rate of medullary thyroid cancer  based on people diagnosed between 2010 and 2016 is nearly 100% in localized cases, 91% in regional cases, and 38% in distant cases.5 

The combined 5-year survival rate for all stages combined is 89%.5

5- and 10-Year Survival Rates for Medullary Thyroid Cancer

According to a 2011 study, the 5-year survival rate is between 65% and 89% and the 10-year survival rate is between 75% and 87% for medullary thyroid cancer. On average this is lower than the survival rate for other types of thyroid cancers that are more common. For example, the 5-year survival rate for papillary and follicular thyroid cancer is between 90% and 94%.4

Factors Affecting Prognosis

The main factor affecting prognosis in MTC is the stage of disease at diagnosis and the extent of local disease. According to a study published in the journal Cancer, the 10-year survival rate was 95.6% for patients in whom the disease was confined to the thyroid gland, whereas it was 40% for patients whose disease had metastasized to distant locations.6 

The American Joint Committee on Cancer (AJCC) defines four stages of MTC, which take into account the size of the tumor, any evidence of regional lymph nodes, and distant metastases. According to this, in stage I, the tumor is 2 cm or smaller in diameter and confined to the thyroid. In stage II, it is larger than 2 cm but either confined to the thyroid or growing outside of the thyroid but not involving nearby structures. In stage III, it can be of any size, and has spread to lymph nodes in the neck but not to other lymph nodes or to distant sites. Finally, in stage IV, cancer can be of any size and has grown beyond the thyroid gland and may or may not be involving nearby structures, such as the larynx, trachea, and esophagus and may or may not have spread to lymph nodes. In advanced stage IV, cancer has spread to distant sites such as the liver, lung, bone, or brain.7

Radiation therapy and chemotherapy do not seem to improve the long-term survival of medullary thyroid cancer patients. The recommended treatment of choice should therefore be total thyroidectomy especially, since the risk of complication increases with repeat surgeries.4,8 

Nomogram Model and Survival Prognostication Tool

A 2020 study used data from 1,237 patients with MTC having undergone total thyroidectomy and neck lymph nodes dissection who enrolled  in the surveillance, epidemiology, and end results (SEER) database to construct a survival prognostication tool for 3- and 5-year overall survival, and cancer-specific survival.9 

Tumor size, age, metastasis status, and lymph node ratio were identified as independent predictors of overall survival and cancer-specific survival.9

Age as a Prognostic Factor

Age may be a prognostic factor in younger patients with MTC having a better survival rate compared to older patients. However, this could be because cases of familial medullary thyroid cancer can be diagnosed by genetic screening. So patients are usually younger when diagnosed with the disease. However, this also means that they are usually at an early stage of the disease.10 Moreover, MTC is usually asymptomatic and may only be discovered by chance during a routine neck examination or imaging tests done for other reasons. Therefore, most patients are usually diagnosed at advanced stages of the disease.1

According to a study by Simões‑Pereira et al., when patients detected by genetic screening were not taken into account, age did not seem to be a prognostic factor while cancer stage did.10 

References

  1. Medullary Thyroid Cancer. American Thyroid Association. Accessed July 6, 2021.
  2. Calcitonin. You and Your Hormones. February 2018. Accessed July 6, 2021.
  3. Taccaliti A, Silvetti F, Palmonella G, Boscaro M. Genetic alterations in medullary thyroid cancer: diagnostic and prognostic markers. Curr Genomics. 2011;12(8):618-625. doi:10.2174/138920211798120835
  4. Stamatakos M, Paraskeva P, Stefanaki C, et al. Medullary thyroid carcinoma: the third most common thyroid cancer reviewed. Oncol Lett. 2011;2(1):49-53. doi:10.3892/ol.2010.223
  5. Thyroid Cancer Survival Rates, by Type and Stage. American Cancer Society. January 25, 2021. Accessed July 6, 2021.
  6. Roman S, Lin R, Sosa JA. Prognosis of medullary thyroid carcinoma: demographic, clinical, and pathologic predictors of survival in 1252 cases. Cancer. 2006;1;107(9):2134-42. doi: 10.1002/cncr.22244
  7. Thyroid Cancer Stages. American Cancer Society. March 14, 2019. Accessed July 6, 2021.
  8. Sippel RS, Kunnimalaiyaan M, Chen H. Current management of medullary thyroid cancer. Oncologist. 2008;13(5):539-47. doi: 10.1634/theoncologist.2007-0239
  9. Chen L, Wang Y, Zhao K, Wang Y, He X. Postoperative nomogram for predicting cancer-specific and overall survival among patients with medullary thyroid cancer. Int J Endocrinol. 2020;22;2020:8888677. doi: 10.1155/2020/8888677
  10. Simões-Pereira J, Bugalho MJ, Limbert E, Leite V. Retrospective analysis of 140 cases of medullary thyroid carcinoma followed-up in a single institution. Oncol Lett. 2016;11(6):3870-3874. doi: 10.3892/ol.2016.4482

Article reviewed by Harshi Dhingra, MD, on July 1, 2021.

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