Follicular 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 subtype including 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
In 1811, the first thyroid cancer case was reported. Thyroid cancer was first described by William Stewart Halsted, an American surgeon in the late nineteenth century.
Classification
Follicular thyroid cancer may be classified according to WHO classification into 2 subtypes including minimally invasive follicular thyroid carcinoma, and widely invasive follicular thyroid carcinoma.
Pathophysiology
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.
Causes
Follicular thyroid cancer is caused by a mutation in the RAS gene
Differential Diagnosis
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.
Epidemiology and Demographics
The incidence of follicular thyroid cancer is estimated to be 0.82 per 100 000 person-years. Females are more commonly affected with follicular thyroid cancer than males. The female to male ratio is approximately 3 to 1. The incidence of follicular thyroid cancer increases with age; the median age at diagnosis is 45 to 50 years.
Risk Factors
Common risk factors in the development of follicular thyroid cancer are iodine deficiency, family history of thyroid cancer, radiation exposure, and age.
Natural history, Complications and Prognosis
Depending on the extent of the tumor at the time of diagnosis, the prognosis of follicular thyroid cancer may vary. However, the prognosis is generally regarded as poor. The presence of metastasis is associated with a particularly poor prognosis among patients with follicular thyroid cancer.
Staging
According to the American Joint Committee on Cancer (AJCC) there are 4 stages of follicular 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 follicular thyroid cancer is swelling in the neck. A positive history of irradiation of head and neck, rapid growth of the nodule, hoarseness of voice, and family history of follicular carcinoma is suggestive of follicular thyroid cancer. The most common symptoms of follicular thyroid cancer include swelling in the neck, pain in the front of the neck, and hoarseness of voice.
Physical Examination
Patients with follicular thyroid cancer usually appear thin and cachectic. Physical examination of patients with follicular 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.