Surgery
Surgery is the most common treatment of thyroid cancer, it is also the most common cause of acquired hypoparathyroidism. For example, during surgery on the thyroid gland, the parathyroid glands may be accidentally damaged or removed.
Radiation therapy
Radiation therapy is a cancer treatment that uses high-energy x-rays or other types of radiation to kill cancer cells or keep them from growing. There are two types of radiation therapy. External radiation therapy uses a machine outside the body to send radiation toward the cancer. Internal radiation therapy uses a radioactive substance sealed in needles, seeds, wires, or catheters that are placed directly into or near the cancer. The way the radiation therapy is given depends on the type and stage of the cancer being treated.
Radiotherapy can cause general side effects such as tiredness. Radiotherapy to the neck can also cause specific side effects such as pain on swallowing, a dry mouth and darker, or red, sore skin.
Ability to become pregnant or father children is not affected by external radiotherapy treatment for thyroid cancer, but it's advisable to wait for at least a year.
Radiotherapy treatment because of a cancer in the neck or the chest can damage the parathyroid glands and make them underactive.
Radioactive iodine
Iodine is an essential component of thyroid hormones, therefore the thyroid uptakes it very intensively and the thyroid tissue is the only one that can uptake it. The Thyroid can not differentiate normal iodine from radioactive iodine, for this reason radioactive iodine is normaly uptaken from the tyroid gland. I-131 is a Beta-emitter, this limits side effects on other tissues, but the associated gamma emission may expone other organs (such as the parathyroids) to damage.
Follicular and papillary thyroid cancers are sometimes treated with radioactive iodine (RAI) therapy. Higher doses than the amounts used to diagnose thyroid cancer are used. RAI is taken by mouth and collects in any remaining thyroid tissue, including thyroid cancer cells that have spread to other places in the body. Since only thyroid tissue takes up iodine, the RAI mainly destroys thyroid tissue and thyroid cancer cells without harming other tissue. Excess of Iodine is eliminated fast from the body and dameged thyroid cells loose their capacity of uptaking it. One of the problems in RAI therapy is that not all thyroid tumors take up iodine, so before treatment a small test-dose is given.
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Acute effects: The acute side effects of I-131 therapy include painful swelling of the salivary glands and nausea.
Rarely, in patients with significant residual thyroid tissue, radioactive iodine may cause acute thyroiditis, with a rapid release of thyroid hormone.
Patients must also be cautioned not to wear contact lenses for at least 3 weeks following ingestion of I-131, as the tears are radioactive and will contaminate the lenses and possibly lead to corneal ulceration.
Bone marrow suppression and leukemia are potential long-term complications of I-131 therapy but are poorly documented and appear to be extremely rare. Leukemia occurs rarely with doses of I-131 < 1,000 mCi.
Pulmonary fibrosis may be seen in patients with pulmonary metastases from papillary or follicular thyroid cancer who are treated with I-131. Those with a miliary or micronodular pattern are at greater risk, as a portion of normal lung around each lesion may receive radiation, leading to diffuse fibrosis.
Effects on fertility Recent data have documented an increase in follicle-stimulating hormone (FSH) levels in one-third of male patients treated with I‑131. Changes in FSH after one or two doses of I-131 are generally transitory, but repeated doses may lead to lasting damage to the germinal epithelium.
The effects of I-131 on female fertility have been investigated. It is generally recommended to avoid pregnancy for 1 year after therapeutic I-131 administration.
Chemotherapy
Chemotherapy is a cancer treatment that uses drugs to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing.
Thyroid hormone therapy
Hormone therapy is a cancer treatment that removes hormones or blocks their action and stops cancer cells from growing. In the treatment of thyroid cancer, drugs may be given to prevent the body from making thyroid-stimulating hormone (TSH), a hormone that can increase the chance that thyroid cancer will grow or recur.
Also, because thyroid cancer treatment kills thyroid cells, the thyroid is not able to make enough thyroid hormone. Patients are given thyroid hormone replacement pills.
Source:National Cancer Institute
