Thyroid cancer is cancer that arises from the thyroid gland. It is more common in women than men. In Singapore, it is the 8th most common cancer diagnosed in women. It is commonly diagnosed at a younger age than most other cancers and most cases occur in patients less than 60 years old. The incidence of thyroid cancer appears to be rising, but this appears to be mostly due to the increased use of ultrasound scanning, picking up more thyroid nodules that may not have been discovered in the past.
There are many types of thyroid cancers.
Differentiated Thyroid Cancers
1. Papillary Thyroid Cancer
This is the most common kind of thyroid cancer seen, accounting for about 75% of thyroid cancers. Papillary thyroid cancers usually are slow growing but they have a tendency to spread to the lymph nodes in the neck. However, most of these cancers can still be treated successfully.
There are many subtypes of papillary thyroid cancer. Some less common subtypes (follicular variant, tall cell, insular, diffuse sclerosing) tend to have more aggressive behaviour and may grow and spread more quickly.
2. Follicular Thyroid Cancer
Follicular thyroid cancer is the second most common type of thyroid cancer seen, accounting for about 15% of cases. These cases tend to spread via the bloodstream to other parts of the body such as the lungs and bones.
3. Medullary Thyroid Cancer
Medullary thyroid cancer is much less common and accounts for about 5% of thyroid cancers. These cancers arise from the parafollicular C cells in the thyroid gland. These cells usually are responsible for producing a hormone called calcitonin, which helps to control the level of calcium in the body.
About 20% of these cases are hereditary (familial medullary carcinoma). Patients with familial medullary thyroid carcinoma tend to develop thyroid cancers at an earlier age in childhood and may also develop other types of cancers (e.g. phaeochromocytoma, parathyroid tumours).
Although the outcome of treatment for medullary thyroid cancer is not as good as for papillary and follicular thyroid cancers, many patients can still be treated successfully.
4. Anaplastic Thyroid Cancers
This type of cancer accounts for about 2% of thyroid cancers. These cancers tend to be very aggressive tumours and grow very quickly and spread rapidly to other parts of the body. Treatment of these cancers is usually very difficult.
5. Thyroid Lymphoma
This is a very rare cancer that sometimes develops in the thyroid gland. Lymphoma is a type of cancer that arises from white blood cells. These cancers are usually treated with chemotherapy, with or without radiotherapy.
Patients with thyroid cancer often first present with a lump in the neck. Often they may not have been the first to notice the lump and other people may have pointed it out to them.
Thyroid cancers are also sometimes found incidentally when there are nodules in the thyroid gland noted on a scan done on the neck for other reasons. These cancers found this way very often cannot be felt and can only be seen on ultrasound scans. Nevertheless, just because a lump cannot be felt does not mean it is not a cancerous lump and all thyroid nodules should be investigated properly to exclude cancer.
Patients who have advanced thyroid cancer can sometimes present with hoarseness. This can occur when cancer invades the nerves that control the movement of the larynx (voice-box). If the cancer has spread to the lymph nodes in the neck, the patient may also be able to feel other enlarged lumps in the neck. Cancers can also cause breathlessness if they cause compression of the trachea and problems swallowing if they compress on the oesophagus.
1. Thyroid Function Tests
This is a blood test where the levels of your thyroid hormones and thyroid-stimulating hormone (TSH) are measured. If your levels of thyroid hormones are too high (hyperthyroidism), you may experience symptoms such as palpitations, feeling hot easily, irritability, diarrhoea, weight loss and increased appetite. If your thyroid hormone levels are too low (hypothyroidism) you may feel easily tired and lethargic, gain weight easily, constipation, memory loss and feeling cold easily.
2. Ultrasound Scan
In this scan, sound waves are used to produce a picture of your thyroid gland and neck structures on a screen. The ultrasound scan is very useful for evaluating thyroid nodules and to look for features that may indicate that the thyroid nodule is suspicious for cancer. It is also useful for looking for any enlarged lymph nodes in the neck. This scan is painless and there is no ionising radiation involved.
3. Fine-needle Aspiration Cytology (FNAC)
Your doctor may advise you to undergo a biopsy to evaluate the lump if he or her feels it is needed. A fine-needle aspiration biopsy is a procedure where the doctor will pass a small needle through the lump to aspirate some cells for the lump for further testing. These cells will be examined under a microscope to look for signs of cancer. This biopsy is often done using ultrasound to guide the doctor to biopsy the correct place.
4. Computer Tomographic (CT) scan
This scan will usually entail you lying down on a motorised bed that will pass through a scanner to obtain an image. The CT scan uses ionising radiation to produce an image and may involve the use of contrast injected through a vein to make the details of the scan easier to interpret.
The treatment of most thyroid cancers will usually involve surgery. Depending on what the doctor finds he will usually recommend one or more of the following operations.
A thyroidectomy is a removal of the whole or part of the thyroid gland. In cancers, most of the time your doctor will recommend removing the whole thyroid gland (Total thyroidectomy). In certain patients with low risk cancers, an option to remove only half of the thyroid gland may be recommended (Hemi-thryoidectomy).
b. Central compartment dissection
In patients with papillary and medullary thyroid cancer, the cancer tends to spread to the lymph nodes around the thyroid gland. Your doctor may advise you to remove the lymph nodes around the thyroid gland and trachea together with the thyroid gland.
c. Modified radical neck dissection
Thyroid cancer may spread to lymph nodes in the neck at the side of the neck as well. In these cases, your doctor may ask you to undergo an operation to remove lymph nodes in the neck which are positive for cancer.
Radioactive Iodine Treatment
This is a form of targeted radiotherapy that uses a radioactive form of iodine (iodine-131/I-131). Thyroid cells take up and concentrate iodine much more than the rest of the cells in the body, radioactive iodine can be used to selectively administer radiation to thyroid cancer cells with little effect on the rest of the cells in the body.
Radioactive iodine treatment works better for well differentiated thyroid cancers such as papillary and follicular thyroid cancers as these cancers usually take up iodine well. Other cancers such as medullary and anaplastic cancers tend not to take up iodine as well thus do not respond well to radioactive iodine treatment.
Radioactive iodine treatment can be used after surgery to kill any remnant cancer cells left in the body. Radioactive can also be used in cases where cancer has spread to other parts of the body. It can also be used in cases where cancer has come back after being treated previously.
Radioactive iodine is usually administered orally in either a capsule or liquid form. You may be required to be admitted in a single room during the treatment to minimise radiation exposure to other people around you.
External Beam Radiotherapy
This treatment involves using ionising radiation to kill cancer cells. This treatment usually involves directing an external source of radiation into the part of the body treated (e.g. neck) while the patient is lying down.
This treatment is not commonly used but may be used in cases where surgery is unable to remove cancer completely. It is also sometimes used in cases where cancer cells do not readily take up iodine (e.g. anaplastic, medullary thyroid cancers).
Thyroid Hormone Treatment
After removal of the thyroid gland, you will need to take medication to replace your thyroid hormone as there will no longer be thyroid hormone produced in your body.
Thyroid hormone is sometimes given at a higher dose than usual in some cases of cancer to suppress the TSH (thyroid stimulating hormone) levels. This helps to reduce the chance of the cancer relapsing.
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