Thyroid cancer is one of the common forms of cancer. The four main types of thyroid cancer are
- Papillary cancer
- Follicular cancer
- Medullary cancer
- Anaplastic thyroid cancer and other rare cancers
Papillary cancer and its variants are the most common type of thyroid cancer. Patients with this type of cancer have very good survival as it is slow growing and shows good response to treatment.
What are the symptoms of thyroid cancer?
Thyroid cancer commonly presents as a swelling in front of the neck that does not cause any other symptoms. The lump may be noticed by your physician during a routine hospital visit for another illness. In some cases, the lump may be large enough to cause symptoms by pressing on adjacent structures in the neck. These patients can have symptoms of hoarsness of voice, difficulty in swallowing, breathlessness or a vague discomfort in the throat. Pain is uncommon and seen in thyroiditis and rare cancers, such as anaplastic.
How is thyroid cancer diagnosed?
Thyroid cancer is diagnosed based on the results of the ultrasound and FNAC (Fine Needle Aspiration Cytology) examinations. Your doctor may also find certain features on physical examination , which raise a possibility of thyroid cancer. Your doctor may note features, suspicious for cancer on an ultrasound examination. FNAC (also called a needle test) can help confirm the diagnosis of cancer. However in a number of patients, the FNAC can show results which fall in between the benign and cancerous spectrum. In such patients, conformation of the diagnosis can be done only after the lump is surgically removed and examined.
It is also important to remember that blood tests will not diagnose thyroid cancer. TSH test which is commonly done to determine the function of the thyroid gland will be normal in most patients with thyroid cancer.
What are the types of thyroid cancer
Papillary thyroid cancer/ mixed papillary follicular thyroid cancer:
It is the commonest type of thyroid cancer and constitutes about 85% of all thyroid cancers. It grows very slowly and tends to spread to lymph nodes in the neck. However this form of cancer has good prognosis and excellent response to treatment in a majority of patients.
Follicular thyroid cancer:
It constitutes about 10% of all thyroid cancers and is usually seen in older age groups. It has a tendency to spread to distant organs like the lungs or bones, through the blood stream. Overall cure rate is good even though the disease is more aggressive than papillary cancer.Treatment results depend on the size of the tumor and the extent of spread to distant organs.
Medullary thyroid cancer:
It constitutes about 2 to 4% of cases of thyroid cancer. 25% of medullary thyroid cancers have an inherited (familial) basis. Early detection is important for complete cure.
Anaplastic thyroid cancer:
It is seen in 1-2% of patients. It is a fast growing tumor and one of the most aggressive cancers which usually affects older patients. Treatment is least effective in this type of cancer.
How are thyroid cancers treated?
Treatment options for papillary and follicular thyroid cancers are similar. These two types of cancer are together called as differentiated thyroid cancer. Prognosis in these patients depends on tumour size, extent of spread and the age of the patient. Younger patients do better than patients who are more than 55 years of age. Surgery and radioiodine therapy are the primary modalities of treatment for these common types of thyroid cancer
Surgery is the first line of treatment for thyroid cancer. The type of surgery depends on the size of the tumour and whether or not the tumour has invaded the surrounding tissues in the neck. For very small cancers (< 1cm) with no surrounding spread, a simple lobectomy – removal of the involved side of thyroid may be enough. However most patients require total thyroidectomy – complete removal of the thyroid gland, as cancer cells are commonly found in the opposite lobe of the thyroid as well. Lymph node involvement is commonly found, either during initial evaluation or during the surgery. These lymph nodes can be removed at the time of the initial surgery ( central or lateral compartment neck dissection) or later if lymph node involvement develops later on. Patients need to take thyroid hormone supplementation life long after a complete thyroidectomy. (—-link for thyroidectomy page).
Early stage thyroid cancer is completely cured by thyroid surgery alone. If the tumour is larger, or has spread to adjacent areas or lymph nodes, your doctor will also advise radioiodine treatment.
Radioactive iodine therapy
Thyroid cells have the ability to absorb iodine from the bloodstream and concentrate it. A form of radioactive iodine is therefore used to identify and destroy residual thyroid cancer cells after surgery. Radioactive iodine (I-131) is given in the form of a liquid or a capsule. The thyroid cancer cells take up almost all this iodine with very less reaching other organs in the body. The radioactive iodine then destroys the cancer cell from within. Rarely in patients getting higher doses of radioactive iodine for thyroid cancer metastasis, the iodine can affect the salivary glands producing dry mouth.
Patients requiring radioactive iodine therapy, need to have higher levels of TSH before the treatment. This helps improve the uptake of the iodine into thyroid tissue. To achieve this, your doctor will advise you to stop your thyroid hormone pills 3-4weeks before the treatment. You may develop symptoms of hypothyroidism such as fatigue, body ache and dry skin during this period. An alternative way of increasing TSH levels, is by using injections of recombinant TSH. If your doctor plans this method of treatment, you will receive 2 doses of recombinant TSH (rhTSH) before the radioactive iodine dose.
TSH suppressive therapy
All thyroid cancer patients need to take thyroid hormone replacement after their thyroid surgery. The dose of thyroid hormone required depends on the type and extent of thyroid cancer. Patients with low risk or early stage thyroid cancer may only require normal doses of thyroid hormone, to keep their TSH levels in the normal range. Patients with moderate or higher risk thyroid cancer, typically require higher doses of thyroid hormone in order to keep their TSH at low levels. Keeping the TSH at a low level will help in preventing regrowth of the tumour.
Follow-up of thyroid cancer
Regular check-ups are essential for all thyroid cancer patients. Follow-up is usually at 3 to 6 monthly intervals. Your doctor will evaluate you for either recurrence of the tumour, or for residual tumour remaining after the initial treatment. These visits include a careful physical examination, blood tests as well as necessary imaging. The thyroglobulin test is an important blood test, which is repeated at least once every year. This is a protein produced by thyroid cells and gives an early clue towards the presence of thyroid cancer cells in the body. An ultrasound of the neck is also usually done to look for tumour or lymph nodes in the neck. Your doctor may also advise a whole body iodine scan, in order to look for the presence of thyroid cancer in the neck or at other distant sites.
Medullary thyroid cancer
This is a rare tumour which arises from cells called the parafollicular c cells. These cells are present within the thyroid gland and secrete a number of proteins. This cancer is attributed to inherited genetic mutations in up to 25% of patients. Medullary thyroid cancer is usually diagnosed when a patient presents with a nodule in the thyroid or enlarged lymph nodes in the neck. This tumour spreads to the local lymph nodes earlier than the papillary and follicular types of cancer.
Evaluation and management of this rare type of cancer requires an experienced team of doctors, especially as this cancer may be associated with involvement of other organs of the body. These patients need evaluation and treatment for associated conditions such as pheochromocytoma( a tumour of the adrenal glands) and hyperparathyroidism. A genetic test may also be planned if there is suspicion of inherited disease. (link to MTC page)
All patients with medullary thyroid cancer are treated surgically. The type of surgery depends on the extent of disease, local spread and the general health of the patient. All patients will require removal of the thyroid gland together with the lymph nodes of the central compartment of the neck (called central neck dissection). The lymph nodes from the side of the neck may need to be removed if found to be involved with the cancer( called lateral neck dissection).These procedures require an expert thyroid surgeon as complete removal of diseased tissue needs to be achieved, while at the same time concentrating on the integrity of surrounding structures such as the parathyroids and recurrent laryngeal nerves. The aim of an expert surgeon will also include maintaining a normal appearance of the neck, and keeping the scar as small as possible.
Patients require regular follow up with clinical examination, chest X ray, ultrasounds and blood tests. Blood tests are done to look for proteins produced by these cancer cells. Levels of calcitonin and CEA(carcinoembryonic antigen) are checked every 3 to 6 months.
Advanced medullary thyroid cancer may extensively involve surrounding structures like the food pipe(esophagus), wind pipe (trachea) and pharynx. Production of biologically active substances by the tumour can cause symptoms like diarrhoea, flushing or breathlessness. Surgical resection of this tumour by an experienced surgeon is required in these patients. Extensive disease which has spread to distant organs requires treatment with chemotherapy or radionucleide therapy, depending on the condition of the patient.
Patients with this rare cancer have lower cure rates than patients with papillary thyroid cancer. However in patients with early stage medullary cancer, surgery results in complete cure. 10-year survival rates are 90% when all the disease is confined to the thyroid gland, 70% when the cancer has spread to cervical lymph nodes and 20% when the cancer is found in distant sites.
Anaplastic thyroid cancer
This is the most aggressive form of thyroid cancer. It is rare and accounts for 1-2% of all thyroid cancers. It usually affects people who are more than 65 years old. It commonly arises within a thyroid nodule which may have existed for a long period of time. It has a tendency to spread rapidly, and lymph node involvement is seen in 90% of patients at the time of diagnosis. Surgery is done in patients who are diagnosed with an earlier stage of anaplastic thyroid cancer. Patients with advanced cancer are treated with chemotherapy and external beam radiation.