Thyroid Cancer

Classification of thyroid carcinomas.

Thyroid cancers are divided into the following categories:

Papillary, follicular, and Hurthle cell carcinomas arise from follicular cells and are considered to be differentiated thyroid cancers. Patients with these tumors are often treated similarly despite numerous biological differences within these tumors. Medullary Thyroid Carcinoma is also a differentiated thyroid carcinoma, but it arises from a different cell type: C cells (parafollicular cells). It is a more aggressive type of 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 are almost impossible to cure.

What are the 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 may be 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, and later hoarseness may develop. If the cancer is large enough, it may cause difficulty swallowing, shortness of breath if it is pressing on the windpipe, or hoarseness from cancer irritating the nerve that goes to the voice box (the recurrent laryngeal nerve).

What causes thyroid cancer?

Thyroid cancer is more common in people who have a history of radiation exposure, have a family history of thyroid cancer, or have had 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 (i.e., the 1940s, 1950s, and even the 1970s), radiation exposure included X-ray treatments for acne, inflamed tonsils, adenoids, lymph nodes, or an enlarged thymus gland. X-rays were also 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 are no specific blood tests to detect papillary, follicular, Hurthle cell, or anaplastic thyroid carcinomas. A diagnosis of thyroid cancer is solely made based on a fine needle aspiration biopsy of a thyroid nodule. Sometimes a diagnosis is made after surgical removal of a suspicious nodule with the part or whole thyroid gland. Although thyroid nodules are very common (up to 50% of females by age 50 will have nodules), less than 1 in 10 harbor a thyroid cancer.

TREATMENT

What is the treatment for thyroid cancer?

Surgery.

The primary therapy for all forms of thyroid cancer is surgery. The generally accepted approach is to remove one-half or the entire thyroid gland. For some cancers, removal of neck lymph nodes is also indicated. After total thyroidectomy, patients need to be on thyroid hormone for the rest of their lives. If only 1/2 of the thyroid is removed, about 1/2 of patients will not need thyroid hormone supplementation. Often, 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 a 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 produce 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 is 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 these cases, patients do not need to withhold their thyroid hormone replacement, experience fewer side effects from it, and can continue to perform their normal functions and job activities without significant interruption, as would happen with withdrawal therapy. Also, you may be asked to follow a low-iodine diet before the treatment to increase the effectiveness of the radioactive iodine. You can find the diet and low-iodine cookbook on the Thyca.org website (Thyroid Cancer Survivors Association). Once the TSH level is high enough, a whole-body iodine scan is performed by administering a small dose of radioactive iodine to determine whether remaining thyroid cells 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 restarted. Sometimes a higher empiric dose is given first, followed by the iodine scan. This is performed to reduce the initial response to a small dose, which may compromise subsequent therapy with a 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 side effects in about 10% of patients (dose-dependent). It may cause dry mouth or a short-term loss of taste or smell after receiving radioactive iodine treatment. To prevent those side effects, during treatment with radioactive iodine, patients are encouraged to drink plenty 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, as well as blood tests to determine whether any changes to your thyroid hormone dose are needed. In particular, blood tests measure T4, TSH, and 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 indicates following up a patient with thyroid cancer is a neck ultrasound, which can detect recurrence or lymph node metastasis in the neck. If thyroglobulin remains detectable despite a low TSH, it suggests that potential thyroid cancer cells are still functioning in the body. This finding may lead to additional tests and possible further treatment with radioactive iodine and/or surgery. Unfortunately, in some patients with thyroid cancer, 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 you 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. 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 has 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 can live a long time and feel well despite their cancer.

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