Thyroid cancer arises from cells within the thyroid gland, it is less common compared to breast, colon, lung and other types of cancers. Although it is less common in the United states and other countries, rates seem to be increasing especially over the past 20 years, partly due to increased early detection of small papillary thyroid cancers secondary to a widespread use of neck ultrasound and fine needle aspiration of thyroid nodules. Prevalence and incidence of thyroid cancer tends to be more in females than males at an estimated ratio of 2:1, most affected are between the ages of 40-60 years however thyroid cancer can develop at any age especially if there is an inherited genetic mutation.
Types of thyroid cancer
Papillary thyroid cancer – This is the most common type (70-80%), has the best prognosis if diagnosed early and can occur at any age. It usually grows slowly (months to years) and can spread to neck lymph nodes, however even with spread to the lymph nodes most of the time it has a very good prognosis.
Follicular thyroid cancer – Accounts for 10-15% of thyroid cancers, can spread to lymph nodes and more likely to spread to other organs than papillary type. It also has a good prognosis if diagnosed and treated early.
Medullary thyroid cancer – accounts for 1-2% of thyroid cancers, usually sporadic but up to 25% can be part a familial genetic syndrome caused by an inherited genetic mutation (MEN syndromes). If diagnosed early and a test of mutated gene is identified this could lead to diagnosis of other related hormonal disorders.
Anaplastic thyroid cancer – Rare (<2%), more aggressive, rapidly growing tumor with the worst prognosis of all the above types. At diagnosis, depending on the size and extension of the tumor, can present with difficulty breathing/swallowing, hoarseness, cough and sometimes spread to other organs. This type of cancer is classified as an undifferentiated thyroid cancer, meaning it lacks the normal features of cell development seen in the other types of cancers hence making it an aggressive type of cancer
What causes thyroid cancer? (Risk factors for thyroid cancer)
There are several known causes of thyroid cancer however in most people the cause is not known. Some of the known causes or risk factors include:
High dose radiation exposure to the neck in childhood is the most clearly defined risk factor associated with benign and cancerous thyroid tumors. Prior to the 1960s high dose radiation was used in most benign and malignant childhood conditions. Other forms of exposure include fallout from atomic weapons and nuclear plant accidents.
Family history – having a first-degree relative with thyroid cancer increases the risk of thyroid cancer, up to 10-fold in some studies. The risk is even higher if there is a family history of known cancer syndromes (Multiple endocrine neoplasia, Carney complex, Cowden syndrome, familial polyposis etc.).
What are the symptoms of thyroid cancer?
The most common presentation of thyroid cancer is as a thyroid nodule, which could have been noticed by a physician/patient or by imaging of the neck (CT scan, MRI, Ultrasound). Most of thyroid cancers are asymptomatic at diagnosis. Some advanced or large tumors can compress vital structures on the neck causing difficulty swallowing/breathing, cough, hoarseness and rarely pain on the neck. Regardless of how the thyroid nodule is discovered thyroid cancer is usually made by fine needle aspiration.
Treatment
Treatment of thyroid cancer can be divided into:
Surgery
Radioactive iodine treatment/Radiation
Replacement of thyroid hormone
Surgery– this is the main and primary form of treatment for all types of thyroid cancer including the advanced ones. The aim is to remove all or as much thyroid tissue as possible. The extent of removal of the thyroid and lymph nodes depends on the findings prior to surgery. If the results from fine needle aspiration was suspicious for cancer and the nodule/tumor is only confined to the thyroid, a lobectomy (removal of the affected lobe) can be done as opposed to removal of the entire thyroid (total thyroidectomy). However if the result from fine needle aspiration was positive for cancer then removal of the entire thyroid gland is indicated. If there are suspicious lymph nodes involved the surgeon might remove some or all of the affected lymph nodes depending on the extend of surgery.
Radioactive iodine (I-131) therapy– since thyroid cells in differentiated thyroid cancer take up and concentrate iodine from diet, radioactive iodine is used to kill any remaining thyroid cells and cancer cells to decreases the risk of recurrence and death from thyroid cancer. This treatment is only reserved for bigger tumors (depending on the stage) and/or spread to other organs.
Medullary and anaplastic thyroid cancers do not respond to radioactive iodine, therefore the mainstay of treatment is surgery followed by chemotherapy and external beam radiation if necessary.
Thyroid hormone replacement – this is to restore the normal metabolic functions since the thyroid gland is removed and this also servers as a tumor suppressor for the differentiated thyroid cancer type.
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Prognosis
Overall prognosis of thyroid cancer is excellent with most cancers confined to the thyroid having a 10year survival of almost 100% , however there are some factors that may increase the risk of recurrence and death from thyroid cancer. These prognostic factors include:
Age – risk of recurrence and death increases with increasing age at diagnosis, however there is no specific age cut-off. 10 year survival is still more than 90% for patients diagnosed at 65 years or younger.
Type of cancer – anaplastic cancer has the worst prognosis and some variants of papillary thyroid cancer have a slightly poor prognosis.
Size of the primary tumor – with more risk of recurrence in larger tumors (>4cm in some studies)
Presence of spread to other distant organs increases the risk of mortality depending on the size of spread.
It is worth noting that even with all these above mentioned factors that decrease the survival rates, most people do not die from thyroid cancer as compared to other known aggressive cancers. In fact despite the increased prevalence and incidence of thyroid cancer over the last 20 years, survival and recurrence rates have remained the same.
