Classification of thyroid carcinomas.
Thyroid cancers are divided into following categories:
- Papillary Thyroid Carcinoma
- Follicular Thyroid Carcinoma
- Hurthle Cell Carcinoma
- Medullary Thyroid Carcinoma
- Anaplastic Thyroid Carcinoma
Papillary, follicular and Hurthle cell carcinomas are arise form follicular cells and considered to be differentiated thyroid cancers. Patients with these tumors are often treated similarly despite on numerous biological differences within these tumors. Medullary Thyroid Carcinoma is also differentiated thyroid carcinoma but it arises from the different cell type, C-cell (parafollicular cells). It is more aggressive type of the thyroid cancer and accounts for approximately four to five percent of thyroid carcinomas. A characteristic feature of this tumor is the production of calcitonin. Most medullary thyroid carcinomas are sporadic. However, about 25% of them are familial as part of the multiple endocrine neoplasia syndrome (MEN 2A or 2B) or FMTC syndrome. Most anaplastic (undifferentiated) cancers appear to arise from differentiated cancers and almost impossible to cure.
What are symptoms of thyroid cancer?
The most common sign of thyroid cancer is a lump (nodule) in the thyroid, and most thyroid cancers do not cause any symptoms until very late. The nodule discovered during a routine physical examination or you may notice a lump in your neck while looking in a mirror. A few patients with thyroid cancer complain of pain in the neck, jaw or ear, later hoarseness may develop. If the cancer is large enough, it may cause difficulty swallowing or cause shortness of breath if it is pressing on the windpipe, the hoarseness that can be caused by cancer irritating the nerve which goes to the voice box (recurrent laryngeal nerve).
What causes thyroid cancer?
Thyroid cancer is more common in people who have a history of exposure to radiation, have a family history of thyroid cancer, or personal history of thyroid cancer in the past. However, for most patients, we do not know the specific reason why they develop thyroid cancer.
Exposure of the thyroid to radiation, especially during childhood or teenage years can cause cancer even 20 or 30 years after the exposure. In the past (ie, in the 1940s, 1950s, and even 1970s), radiation exposure included X-ray treatments for acne, inflamed tonsils, adenoids, lymph nodes, or an enlarged thymus gland. X-rays also were used to measure foot sizes in shoe stores. Currently, X-ray exposure is usually limited to treatment of serious cancers such as Hodgkin’s disease (cancer of the lymph nodes), sometimes irradiation for the breast cancer can go as higher as lower neck area. Routine X-ray exposure (eg, dental X-rays, chest X-rays, mammograms) was not reported to cause thyroid cancer.
Thyroid cancer can be caused by absorbing radioactive iodine released during a nuclear power plant disaster such as the 1986 nuclear accident at the Chernobyl power plant in Russia. Children who were exposed were the most affected, and cancers were seen within a few years to 2-3 decades after that disaster. You can be protected from developing thyroid cancer due to a nuclear power plant emergency by taking potassium iodide, which blocks your thyroid from absorbing radioactive iodine.
How is thyroid cancer diagnosed?
There is no specific blood tests to detect papillary, follicular, Hurthle cell or anaplastic thyroid carcinomas. A diagnosis of thyroid cancer is solely made on the basis of a fine needle aspiration biopsy of a thyroid nodule. Sometimes diagnosis is made after surgical removal of suspicious nodule with the part or whole thyroid gland. Although thyroid nodules are very common (up to 50% of the female by age 50 will have nodules), less than 1 in 10 harbor a thyroid cancer.
What is the treatment for thyroid cancer?
The primary therapy for all forms of thyroid cancer is surgery. The generally accepted approach is to remove the one half or entire thyroid gland. For some cancers removal of neck lymph nodes is indicated as well. After total thyroidectomy, patients need to be on thyroid hormone for the rest of their life. If only 1/2 of the thyroid removed then about 1/2 of the patient will not need to have any thyroid hormone supplementation. Often the thyroid cancer is cured by surgery alone, especially if the cancer is small. If the cancer is large within the thyroid and/ or if it has spread to lymph nodes and you are at high risk for recurrent cancer, radioactive iodine therapy can be used as pill given to destroy thyroid cancer cells after removal of the thyroid gland by surgery.
Radioactive iodine therapy.
A major reason for the usually excellent prognosis for patients with papillary and follicular thyroid carcinoma, and even Hurthle cell thyroid carcinoma, is that radioactive iodine can be used to destroy residual thyroid cancer cells with little or no damage to other tissues in the body. Thyroid cells normally concentrate iodine from the bloodstream to use to produce the thyroid hormones. By contrast, thyroid cancer cells usually take up only tiny amounts of iodine. However, high levels of thyroid stimulating hormone (TSH) can arouse thyroid cancer cells to take up significant amounts of iodine.
If radioactive iodine therapy used, high levels of TSH will be produced in your body by making you hypothyroid for a short time—either by not starting thyroid hormone pills after the thyroid gland is removed or by stopping your thyroid hormone pills if you are already on medication. Sometimes, to minimize your symptoms of hypothyroidism, your doctor may prescribe Cytomel™ (T3) to take while you are becoming hypothyroid. Another option is to use synthetic thyroid stimulating hormone - Thyrogen. In this cases patient do not need to withhold their thyroid hormone replacement, have less side effect from that and can continue to perform their normal function and job activities without significant interruption as it would happened with withdraw therapy. Also, you may be asked to go on a low iodine diet before the treatment to increase the effectiveness of the radioactive iodine. You can see diet and low iodine cook book on Thyca.org website (thyroid cancer survival association). Once the TSH level is high enough, a whole body iodine scan is done by administering a small dose of radioactive iodine to determine if there are remaining thyroid cells that need to be destroyed. If enough cells show up on the whole-body iodine scan, a large dose of radioactive iodine (I-131) is given, and then the thyroid pills are re-started. Sometimes higher empiric dose is giving first, following by the iodine scan. This is performed in order to decrease initial response to small dose which may compromise following therapy with the large dose.
Radioactive iodine therapy has even been able to cure cases of thyroid cancer that had already spread to lymph nodes and other organs. But administration of high doses can cause some side effects in about 10% of the patients (dose depended effects). It may cause dry mouth or lose their sense of taste or smell for a short period of time after receiving radioactive iodine treatment. In order to prevent those side effects, during treatment with radioactive iodine, patients are encouraged to drink lots of water and other fluids. Chewing sugar-free gum or sucking on sugar-free hard candy may help.
Although radioactive iodine usually does not cause loss of fertility in women, it may cause some effect on the fetus and it is recommended that women avoid pregnancy for one year after radioactive iodine therapy.
Patients with medullary thyroid and anaplastic thyroid carcinomas do not respond to and do not receive I-131 treatment.
What is the follow-up for patients with thyroid cancer?
Periodic follow-up examinations are essential for all patients with thyroid cancer because the thyroid cancer can return—sometimes many years after the apparently successful initial treatment. These follow-up visits include a careful history and physical examination, with particular attention to the neck area, as well as blood tests to determine if any changes of your thyroid hormone dose are needed. In particular, blood tests are done to measure the levels of T4 and TSH as well as a thyroid cell protein, thyroglobulin, which serves as a thyroid cancer marker. The thyroid hormone dose is adjusted to lower the TSH level into the low range. Another test that absolutely indicated to follow patient with thyroid cancer is neck ultrasound, that can detect recurrence or lymph nodes metastasis in the neck. If the thyroglobulin level is still detectable despite a TSH in the low range, it means that there still are potential thyroid cancer cells functioning in the body. This finding may lead to additional tests and possible further treatment with radioactive iodine and/or surgery. Unfortunately, in some thyroid cancer patients the presence of interfering antibodies in the blood may prevent accurate thyroglobulin measurement.
In addition to routine blood tests, periodically a whole-body iodine scan may be repeated to determine if any thyroid cells remain. This can be done after your TSH level is raised, either by stopping your thyroid hormone and your becoming hypothyroid or by administering Thyrogen™ (synthetic human TSH) injections.
What is the prognosis of thyroid cancer?
Overall, the prognosis of thyroid cancer is very good for papillary, follicular and even Hurthle cell carcinomas. In general, the prognosis is better in younger patients than in those over 40 years of age. Patients with papillary carcinoma who have a primary tumor that is confined to the thyroid gland itself have an excellent outlook and complete recovery is achieved in up to 95% of the patients: only 1 out of every 100 such patients have died of thyroid cancer by 25 years later. The prognosis is not quite as good in patients over the age of 40, or in patients with tumors larger than 4 centimeters (1½ inches) in diameter. Still, even those patients who are unable to be cured of their thyroid cancer are able to live a long time and feel well despite their cancer.