Thyroid cancer can be caused due to a number of inherited conditions, but the exact cause of most thyroid cancers is yet to be found. Few changes in a DNA sequence can turn the thyroid cells cancerous which makes up to be one of the most frequent of thyroid cancer causes.
Cancers can be caused by DNA changes which turn on the oncogenes, genes responsible for cell division or turn off the tumour suppressor genes, genes that slow down cell division, repair DNA and promote cell death. The DNA changes may happen due to external agents like radiation or they may just be random events that sometimes happen in a cell. Read more about thyroid cancer here.
What are the causes of thyroid cancer?
The changes in DNA noted in each type of thyroid cancer are listed as follows:
Papillary thyroid cancer:
Several DNA mutations have been found in people diagnosed papillary thyroid cancer and many of these cancers have changes in specific parts of the RET gene, a gene that provides instructions for producing a protein involved in signalling within the cells.
- The PTC oncogene, an altered gene is found in about 10% to 30% of papillary thyroid cancers. These RET mutations are not inherited nor passed on but acquired over time so do not pass from parent to child.
- The BRAF mutation is also seen in many cases of papillary thyroid cancer though it is less common in children with thyroid cancer and in cases where exposure to radiation is a potential cause. The cancers with BRAF gene mutation grow and spread to the other parts of the body more quickly.
- Changes in other genes including those in the NTRK1 gene and the MET gene have been linked to papillary thyroid cancer.
Follicular thyroid cancer:
Changes acquired in the rearrangement of the following are responsible for follicular thyroid cancer:
- RAS oncogene
Anaplastic thyroid cancer:
Anaplastic thyroid cancer is often caused because of the changes in the:
- TP53 tumor suppressor gene
- CTNNB1 oncogene
Medullary thyroid cancer:
People who have medullary thyroid cancer (MTC) have:
- Mutations in different parts of the RET gene however are in these are in different parts when compared to papillary carcinoma patients.
- Most patients with sporadic MTC have gene mutations only in their cancer cells however those with familial MTC and MEN 2 mutations are in every cell of the patient’s body and can be detected easily by a test of the DNA of blood cells.
Know more about diagnosis of thyroid cancer here.
What are the risk factors of thyroid cancer?
When the exact causes of a disease are not known, certain factors that are involved with it are noted and these are called the risk factors. The risk factors are the conditions that suggest higher probabilities for developing a certain disease, in this case thyroid cancers. Presence of risk factors does not imply that a person will get cancer but only indicates likelihood. Same is true with the converse, a person can get thyroid cancer even in the absence of all the risk factors. Some risk factors for thyroid cancer are as follows:
Age and gender:
For reasons still not very clear, thyroid cancer is more frequent in women than in men and while it can occur at any age, but the risk peak age earlier for women (who are mostly in their 40s or 50s when diagnosed) is lower than when compared to men (who are usually affected in their 60s or 70s).
Several inherited genetics are linked directly to different types of thyroid cancer. However, not all patients inherit thyroid cancer. The familial medullary thyroid carcinoma (FMTC) can occur alone or it can be seen along with other tumors, called MEN 2.
Patients with inherited medical conditions of certain kind have a higher risk of more common forms of thyroid cancer. Higher rates of thyroid cancer may occur among people with uncommon genetic conditions like: Familial adenomatous polyposis (FAP), Cowden disease, Carney complex- type I, familial nonmedullary thyroid carcinoma. Having a direct relative like parent, brother, sister or a child with thyroid cancer even without a known inherited syndrome in the genes may increase one’s risk of thyroid cancer. The genetic basis for certain cancers is not totally clear yet.
A diet low in iodine:
Follicular thyroid cancers are very common in areas where diets contain low content of iodine. However, most people get enough iodine in their diet because it is added to table salt and other foods as a part of food regulations. A diet low in iodine combined with exposure to radioactivity may also increase the risk of papillary cancer in a person.
Exposure to radiation is a major risk factor for thyroid cancer. The radiation may have been caused because of medical treatments and radiation fallout from power plant accidents or nuclear weapons.
The probability of thyroid cancer is high if head or neck radiation treatments has been received in early stages. The risk, however depends on the amount of radiation given and the age when treatment was received. Generally, the risk will increase with high doses and with younger age at the time of treatment.
The risk factors of thyroid cancer are not completely known which makes it very difficult to be able to prevent it in all cases. Radiation exposure, especially in childhood, is a known thyroid cancer risk factor. Imaging tests such as X rays and CT scans also expose children to radiation, to be safe, children should not have tests unless there is an absolute necessity that too using the minimal dosage to get a clear picture.
Regular blood tests have to be done to look for the gene mutations found in familial medullary thyroid cancer (MTC). Once the disease is discovered in a family, the rest of the family members can be tested for the mutated gene. Removal of the thyroid gland in children who are suspected to carry a abnormal gene will most probably prevent a cancer that might have otherwise been fatal.