Thyroid cancer is estimated to be the 7th most common type of cancer among females and 14th most common cancer among males. In India, the incidence rates of thyroid cancer in females is 1%–5% and in males is 2%.
Thyroid is a small, butterfly-shaped gland located in lower front of the neck, just below the Adam’s apple. The thyroid gland controls the body’s metabolism by releasing hormones that regulate several functions in the body, such as utilising energy, producing heat, consuming oxygen, regulating heart rate, blood pressure, etc.
About thyroid cancer
Thyroid cancer occurs when there is a sudden change or a mutation in the cells, causing the abnormal cells to form. These abnormal cells multiply in the thyroid gland to form a tumour. If the cancer is diagnosed early, it can be treated successfully.
The incidence of thyroid cancer appears to be increasing. Experts believe that this can be attributed to the advancements in technology which allow the identification of small thyroid cancers, which may not have been found in the past.
There are various types of thyroid cancers; some are aggressive, while some grow very slowly. However, most can be cured with treatment.
Types of thyroid cancer
Thyroid cancers can be classified into the following types based on the type of cells found in the tumor.
Papillary thyroid cancer is the most common type. It develops from the follicular cells (produce and store thyroid hormones), usually only in one lobe of the gland. The cancer tends to grow very slowly, but usually spreads to the lymph nodes in the neck. This type of cancer is common among 30 to 50-year-old people, but it can occur at any age.
Follicular thyroid cancer is the next most common type, which usually occurs in regions where people do not consume enough iodine in their diet. It also arises from the follicular cells of the thyroid. This type of cancer rarely spreads to the lymph nodes in the neck, but often spreads to the bones or lungs. It is common among individuals who are more than 50 years old.
Anaplastic thyroid cancer or undifferentiated carcinoma is a rare type of thyroid cancer that develops from the follicular cells. It usually spreads quickly to the neck lymph nodes and other parts of the body, and hence is very difficult to treat. This type of cancer typically occurs in 60-year-old individual or older.
Medullary thyroid cancer begins in the C cells of the thyroid gland (produce calcitonin hormone). An elevated level of calcitonin can suggest this cancer at the initial stages. This type of cancer is difficult to find, and it can spread to the lymph nodes, lungs, or liver before being discovered.
Other rare types of thyroid cancer include thyroid sarcoma, which starts in the connective tissue cells of the thyroid, and thyroid lymphoma, which begins in the immune system cells of the thyroid.
Causes/ Risk factors
The exact cause of thyroid cancer is not clear.
When the thyroid cells undergo genetic changes or mutations, the cells lose the ability to die like a normal cell, thus they grow and multiply rapidly. These abnormal cells accumulate to form a tumor and can spread to the surrounding tissues and organs (metastasize).
Certain factors can increase the risk of thyroid cancer; these include:
- Female sex
- Exposure to radiation
- Some genetic syndromes, such as multiple endocrine neoplasia
Signs and symptoms
Typically, thyroid cancers do not present any symptoms in the early stage. As the cancer grows, it may cause the following symptoms:
- A lump (nodule) in the neck
- Difficulty swallowing
- Trouble breathing
- Changes in the voice, including hoarseness
- Pain when swallowing
- Swollen lymph nodes in the neck
Tests that can detect and diagnose thyroid cancer include:
Physical exam: The patient’s neck is checked for any swelling or lumps. The patient may be asked if they were exposed to radiation recently or if they have a history of thyroid tumors.
Blood tests: Blood samples may be analysed to evaluate the functioning of the thyroid gland.
Ultrasound imaging: An ultrasound of the lower neck may be performed to check for any nodules and if they are noncancerous (benign) or cancerous.
Fine-needle aspiration biopsy: A thin long needle is inserted through the skin, precisely into the thyroid nodule, with the help of ultrasound imaging. Thereafter, a sample of the suspicious thyroid tissue is removed using a needle, which is analysed for cancer cells in the laboratory.
Other imaging tests: One or more imaging tests may be performed to help the doctor determine if the cancer has spread beyond the thyroid gland. These tests may include MRI, CT, and nuclear imaging tests.
Staging of thyroid cancer
Thyroid cancer is staged using the TNM staging system. This provides details about:
- Tumor (T): Size and location
- Node (N): Number and location of the tumor spread to the lymph nodes (if any)
- Metastasis (M): Size and location of the cancer spread to other parts of the body (if any)
Based on this system, thyroid cancer has the following stages:
Stage I: Small tumor with or without spread to lymph nodes.
Stage II: A larger localized tumor, with or without spread to lymph nodes.
Stage III: Tumor >4 cm confined to thyroid, but may have minimally spread outside the thyroid.
Stage IV: This stage is classified into three more substages based on whether the tumor has spread to nearby structures, or to the lymph nodes, or to distant organs.
Most types of thyroid cancers can be treated successfully. The treatment options for thyroid cancer depend on the type, stage, overall health and preferences of the patient.
Some of the treatment options for thyroid cancer have been discussed below:
Surgery is a common treatment method for thyroid cancer. One of the following surgical procedure may be used:
- Thyroidectomy: All of the thyroid tissue (total thyroidectomy) or most of the thyroid tissue (near-total thyroidectomy) may be removed.
- Thyroid lobectomy: Half of the thyroid is removed in this procedure. The lymph nodes near the cancer may also be removed.
- Lymph node dissection: The lymph nodes in the neck may be removed during a thyroidectomy in this procedure.
Radiation therapy involves directing high-energy X-rays or other types of radiation to the cancer cells to kill or prevent them from growing. The two type of radiation therapy used to treat thyroid cancer include:
External radiation therapy: In this method, a machine aims high-energy beams towards the cancer from outside the body.
Radioactive iodine treatment: In this method, large doses of radioactive iodine in a capsule or a liquid is given. This iodine is absorbed by the thyroid cells first, and later by the thyroid cancer cells; hence, there is a low chance of affecting other cells in the body.
Chemotherapy involves usage of drugs to kill cancer cells. These drugs travel throughout the body and kill rapid growing cells. Chemotherapy is sometimes recommended for anaplastic thyroid cancer treatment.
Targeted drug therapy
Targeted drug therapy involves giving drugs that target the signals of cell growth and division of thyroid cells. These drugs may include certain tyrosine and protein kinase inhibitors.
Thyroid hormone therapy
In this treatment method, patients are given thyroid hormone medication levothyroxine, usually for those who underwent thyroid cancer treatment, such as thyroidectomy. The thyroid cancer treatment kills the thyroid cells, and hence is not able to produce sufficient amounts of thyroid hormone. Levothyroxine supplies the missing hormone. This medication also inhibits the pituitary gland from producing thyroid-stimulating hormone (TSH). High TSH levels can induce any remaining cancer cells to grow.
Most individuals with thyroid cancer have no known risk factors. Hence, there is no definite way of preventing thyroid cancer.
However, here are some measures that may prevent thyroid cancer:
Avoid getting exposed to radiation: Radiation should not be used to treat less serious diseases. Imaging tests like X-rays and CT scans must not be performed, particularly in children, unless they are absolutely needed.
Take medicine: Individuals who live near nuclear power plants, or in case of a nuclear reactor accident, a medication that blocks the effects of radiation is provided. This medication must be taken only if recommended by a doctor.
Get tested: Individuals who have a family history of medullary thyroid cancer can undergo genetic tests to look for gene mutations. If a person is at risk of thyroid cancer, the thyroid gland can be removed, and thyroid cancer can be prevented. A genetic counsellor can give a clear picture about the risk of thyroid cancer.
Most cases of thyroid cancer are treated completely. Papillary and follicular thyroid cancers are usually treated with complete removal of the thyroid gland lobe that harbors cancer. Thyroid gland is completely removed when the gland has a nodule within it, or has multiple other nodules in both sides, or when cancer has spread to lymph nodes in the neck. Expert evaluation, timely diagnosis, and treatment by the best suitable method can result in best outcomes for the patient.
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