Medullary thyroid cancer overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ammu Susheela, M.D. [2]
Overview
Thyroid cancer was first described by William Stewart Halsted, an American surgeon in the late nineteenth century. Follicular thyroid cancer may be classified according to WHO classification into 2 subtypes: minimally invasive follicular thyroid carcinoma, and widely invasive follicular thyroid carcinoma. Follicular thyroid cancer arises from follicular cells of thyroid, which are secretory cells that are normally involved in production and secretion of thyroid hormones, thyroxine (T4)and triiodothyronine (T3). Genes involved in the pathogenesis of follicular thyroid cancer include Ras, PAX8/PPARγ, and PTEN. Follicular thyroid cancer must be differentiated from other diseases that cause neck masses such as goiter, Grave's disease, Hurthle cell carcinoma, anaplastic thyroid carcinoma, papillary thyroid carcinoma, and medullary thyroid carcinoma. The incidence of follicular thyroid cancer is estimated to be 0.82 per 100 000 person-years. The female to male ratio is approximately 3 to 1. Common risk factors in the development of follicular thyroid cancer are iodine deficiency, family history of thyroid cancer, radiation exposure, and age. MRI may be helpful in the diagnosis of follicular thyroid cancer. MRI may also be performed to detect metastases of follicular thyroid cancer to brain and bones. On biopsy, follicular thyroid cancer is characterized by trabecular, solid, follicular tumor cells that invade tumor capsule or surrounding vascular structures. Surgery is the mainstay of treatment for follicular thyroid cancer.
Historical Perspective
Medullary thyroid cancer was first discovered by John Beach Hazard, an American pathologist, in 1959.[1]
Classification
Medullary thyroid cancer may be classified according to mode of occurrence into 2 groups: sporadic medullary thyroid cancer and inherited medullary thyroid cancer.
Pathophysiology
Development of medullary thyroid cancer is the result of genetic mutation of RET proto-oncogene. On gross pathology, well circumscribed, gray, white, or yellow in color mass are characteristic findings of medullary thyroid cancer. On microscopic histopathological analysis, polygonal to spindle to small cells, interstitial edema, and vascular hyalinized stroma are characteristic findings of medullary thyroid cancer.
Causes
Medullary thyroid cancer is caused by a mutation in the RET proto-oncogene.
Differential Diagnosis
Medullary thyroid cancer must be differentiated from anaplastic thyroid carcinoma, papillary thyroid carcinoma, and Hurthle cell carcinoma.
Epidemiology and Demographics
The incidence of medullary thyroid cancer is approximately 1000 per 100,000 individuals in United States per year. The incidence of medullary thyroid cancer increases with age; the median age at diagnosis peaks in the 3rd to 4th decades.
Risk Factors
Common risk factors in the development of medullary thyroid cancer are family history of medullary thyroid cancer and family history of multiple endocrine neoplasia.
Screening
According to the American Society of Clinical Oncology, screening for medullary thyroid cancer by RET gene testing is recommended for children with increased risk of medullary thyroid cancer.
Natural history, Complications and Prognosis
If left untreated, patients with medullary thyroid cancer may progress to develop metastasis. Common complications of medullary thyroid cancer include vocal cord compression, dysphagia, and dyspnea. The presence of metastasis is associated with a particularly poor prognosis among patients with medullary thyroid cancer. The 5 year event free survival rate is 80%.
Staging
According to the American Joint Committee on Cancer (AJCC)[2] there are 4 stages of medullary thyroid cancer based on the clinical features and findings on imaging. Each stage is assigned a letter and a number that designate the tumor size, number of involved lymph node regions, and metastasis.
History and Symptoms
The hallmark of medullary thyroid cancer is lump in the neck. A positive family history of medullary thyroid cancer or multiple endocrine neoplasia is suggestive of medullary thyroid cancer. The most common symptoms of medullary thyroid cancer include diarrhea, flushing, and dysphagia.
Physical Examination
Patients with medullary thyroid cancer usually appear thin and cachectic. Physical examination of patients with medullary thyroid cancer is usually remarkable for thyromegaly, lymphadenopathy and anxiety.
Laboratory Findings
Laboratory findings consistent with the diagnosis of follicular thyroid cancer include elevated T3, elevated T4, and decreased thyroid stimulating hormone.
Chest x-ray
Chest x-ray may be helpful in the diagnosis of follicular thyroid cancer.
CT
CT scan may be helpful in the diagnosis of diffuse follicular thyroid cancer.
MRI
MRI may be helpful in the diagnosis of follicular thyroid cancer. MRI may also be performed to detect metastases of follicular thyroid cancer to brain and bones.
Echocardiography or Ultrasound
Neck ultrasound may be performed to detect follicular thyroid cancer.
Other Imaging Findings
Other diagnostic studies for follicular thyroid cancer include radioiodine scan, which demonstrates increased uptake of radioactive iodine at the areas of metastases and laryngoscopy which demonstrates vocal cord immobility.
Biopsy
On biopsy, follicular thyroid cancer is characterized by trabecular, solid, follicular tumor cells that invade tumor capsule or surrounding vascular structures.
Medical Therapy
Patients with follicular thyroid cancer are treated with radioactive iodine therapy and targeted medical therapy.
Surgery
Surgery is the mainstay of treatment for follicular thyroid cancer.
Prevention
Effective measures for the prevention of follicular thyroid cancer include avoidance of diets low in iodine and avoidance of ultraviolet exposure.
Reference
- ↑ HAZARD JB, HAWK WA, CRILE G (1959). "Medullary (solid) carcinoma of the thyroid; a clinicopathologic entity". J. Clin. Endocrinol. Metab. 19 (1): 152–61. doi:10.1210/jcem-19-1-152. PMID 13620740.
- ↑ Stage Information for Thyroid Cancer Cancer.gov (2015). http://www.cancer.gov/types/thyroid/hp/thyroid-treatment-pdq#link/stoc_h2_2- Accessed on October, 29 2015
[[Category:Hereditary cancers