Thyroid cancers are thought to be related to a number of environmental and genetic predisposing factors, but significant uncertainty remains regarding their causes.

Environmental exposure to ionizing radiation from both natural background sources and artificial sources is suspected to play a significant role, and there are significant increased rates of thyroid cancer in those exposed to mantlefield radiation for lymphoma, and those exposed to iodine-131 following the Chernobyl, Fukushima, Kyshtym, and Windscale nuclear disasters. Thyroiditis and other thyroid diseases also predispose to thyroid cancer.

Genetic causes include multiple endocrine neoplasia type 2 which markedly increases rates, particularly of the rarer medullary form of the disease.

The prognosis of thyroid cancer is related to the type of cancer and the stage at the time of diagnosis. For the most common form of thyroid cancer, papillary, the overall prognosis is excellent. Indeed, the increased incidence of papillary thyroid carcinoma in recent years is likely related to increased and earlier diagnosis. One can look at the trend to earlier diagnosis in two ways. The first is that many of these cancers are small and not likely to develop into aggressive malignancies. A second perspective is that earlier diagnosis removes these cancers at a time when they are not likely to have spread beyond the thyroid gland, thereby improving the long-term outcome for the patient. There is no consensus at present on whether this trend toward earlier diagnosis is beneficial or unnecessary.

The argument against early diagnosis and treatment is based on the logic that many small thyroid cancers (mostly papillary) will not grow or metastasize. This viewpoint holds the overwhelming majority of thyroid cancers are overdiagnosed (that is, will never cause any symptoms, illness, or death for the patient, even if nothing is ever done about the cancer). Including these overdiagnosed cases skews the statistics by lumping clinically significant cases in with apparently harmless cancers. Thyroid cancer is incredibly common, with autopsy studies of people dying from other causes showing that more than one-third of older adults technically have thyroid cancer, which is causing them no harm. It is easy to detect nodules that might be cancerous, simply by feeling the throat, which contributes to the level of overdiagnosis. Benign (non-cancerous) nodules frequently co-exist with thyroid cancer; sometimes, it is a benign nodule that is discovered but surgery uncovers an incidental small thyroid cancer. Increasingly, small thyroid nodules are discovered as incidental findings on imaging (CT scan, MRI, ultrasound) performed for another purpose ; very few of these people with accidentally discovered, symptom-free thyroid cancers will ever have any symptoms, and treatment in such patients has the potential to cause harm to them, not to help them.

Thyroid cancer is three times more common in women than in men, but according to European statistics, the overall relative 5-year survival rate for thyroid cancer is 85% for females and 74% for males.

The table below highlights some of the challenges with decision making and prognostication in thyroid cancer. While there is general agreement that stage I or II papillary, follicular or medullary cancer have a good prognosis, it is not possible when evaluating a small thyroid cancer to determine which ones will grow and metastasize and which will not. As a result, once a diagnosis of thyroid cancer has been established (most commonly by a fine needle aspiration), it is likely that a total thyroidectomy will be performed.

This drive to earlier diagnosis has also manifested itself on the European continent by the use of serum calcitonin measurements in patients with goiter to identify patients with early abnormalities of the parafollicular or calcitonin-producing cells within the thyroid gland. As multiple studies have demonstrated, the finding of an elevated serum calcitonin is associated with the finding of a medullary thyroid carcinoma in as high as 20% of cases.

In Europe where the threshold for thyroid surgery is lower than in the United States, an elaborate strategy that incorporates serum calcitonin measurements and stimulatory tests for calcitonin has been incorporated into the decision to perform a thyroidectomy; thyroid experts in the United States, looking at the same data sets have, for the most part, not incorporated calcitonin testing as a routine part of their evaluation, thereby eliminating a large number of thyroidectomies and the consequent morbidity. The European thyroid community has focused on prevention of metastasis from small medullary thyroid carcinomas; the North American thyroid community has focused more on prevention of complications associated with thyroidectomy (see American Thyroid Association guidelines below). It is not clear at this time who is correct.

As demonstrated in the Table below, individuals with stage III and IV disease have a significant risk of dying from thyroid cancer. While many present with widely metastatic disease, an equal number evolve over years and decades from stage I or II disease. Physicians who manage thyroid cancer of any stage recognize that a small percentage of patients with low-risk thyroid cancer will progress to metastatic disease.

Fortunately for those with metastatic thyroid cancer, the last 5 years has brought about a renaissance in thyroid cancer treatment. The identification of some of the molecular or DNA abnormalities for thyroid cancer has led to the development of therapies that target these molecular defects. The first of these agents to negotiate the approval process is vandetanib, a tyrosine kinase inhibitor that targets the RET proto-oncogene, 2 subtypes of the vascular endothelial growth factor receptor, and the epidermal growth factor receptor. More of these compounds are under investigation and are likely to make it through the approval process. For differentiated thyroid carcinoma, strategies are evolving to use selected types of targeted therapy to increase radioactive iodine uptake in papillary thyroid carcinomas that have lost the ability to concentrate iodide. This strategy would make it possible to use radioactive iodine therapy to treat "resistant" thyroid cancers. Other targeted therapies are being evaluated, making it possible that life will be extended over the next 5–10 years for those with stage III and IV thyroid cancer.

Prognosis is better in younger people than older ones.

Prognosis depends mainly on the type of cancer and cancer stage.

Parathyroid cancer occurs in midlife at the same rate in men and women.

Conditions that appear to result in an increased risk of parathyroid cancer include multiple endocrine neoplasia type 1, autosomal dominant familial isolated hyperparathyroidism and hyperparathyroidism-jaw tumor syndrome (which also is hereditary). Parathyroid cancer has also been associated with external radiation exposure, but, most reports describe an association between radiation and the more common parathyroid adenoma.

Depending on source, the overall 5-year survival rate for medullary thyroid cancer is 80%, 83% or 86%, and the 10-year survival rate is 75%.

By overall cancer staging into stages I to IV, the 5-year survival rate is 100% at stage I, 98% at stage II, 81% at stage III and 28% at stage IV. The prognosis of MTC is poorer than that of follicular and papillary thyroid cancer when it has metastasized (spread) beyond the thyroid gland.

The prognostic value of measuring calcitonin and carcinoembryonic antigen (CEA) concentrations in the blood was studied in 65 MTC patients who had abnormal calcitonin levels after surgery (total thyroidectomy and lymph node dissection). The prognosis correlated with the rate at which the postoperative calcitonin concentration doubles, termed the calcitonin doubling time (CDT), rather than the pre- or postoperative absolute calcitonin level:

- CDT less than 6 months: 3 patients out of 12 (25%) survived 5 years. 1 patient out of 12 (8%) survived 10 years. All died within 6 months to 13.3 years.

- CDT between 6 months and 2 years: 11 patients out of 12 (92%) survived 5 years. 3 patients out of 8 (37%) survived 10 years. 4 patients out of 12 (25%) survived to the end of the study.

- CDT more than 2 years: 41 patients out of 41 (100%) were alive at the end of the study. These included 1 patient whose calcitonin was stable, and 11 patients who had decreasing calcitonin levels.

The calcitonin doubling time was a better predictor of MTC survival than CEA but following both tests is recommended.

According to Surveillance, Epidemiology, and End Results (SEER), the incidence of papillary cancer has increase from 4.8 to 14.9 per 100,000 from 1975 to 2012. Females are more likely to get papillary cancer when compared to males with incidence ratio of 2.5 to 1 where most of the cancers are diagnosed between 40 to 50 years old in females. However, death rates from papillary cancer remains static from 2003 to 2012 at 0.5 per 100,000 men and women. There was an increased incidence of papillary cancer from 1910 to 1960 due to the use of ioninsing radiation in treating childhood head and neck cancers. The incidence decreased after radiation therapy was abondoned. Environmental exposures to radiation such as atomic bombings of Hiroshima and Nagasaki and Chernobyl disaster also causes an increase in childhood papillary thyroid cancer at 5 to 20 years after the exposure to radiation. Family history of thyroid cancer syndrome such as familial adenomatous polyposis, Carney complex, Multiple endocrine neoplasia type 2 (MEN-2), Werner syndrome, and Cowden syndrome increases the risk of getting papillary cancer.

The overall 5-year survival rate for follicular thyroid cancer is 91%, and the 10-year survival rate is 85%.

By overall cancer staging into stages I to IV, follicular thyroid cancer has a 5-year survival rate of 100% for stages I and II, 71% for stage III, and 50% for stage IV.

Based on overall cancer staging into stages I to IV, papillary thyroid cancer has a 5-year survival rate of 100 percent for stages I and II, 93 percent for stage III and 51 percent for stage IV.

Mutations (DNA changes) in the RET proto-oncogene, located on chromosome 10, lead to the expression of a mutated receptor tyrosine kinase protein, termed RET (REarranged during Transfection). RET is involved in the regulation of cell growth and development and its germline mutation is responsible for nearly all cases of hereditary or familial medullary thyroid carcinoma. Its germline mutation may also be responsible for the development of hyperparathyroidism and pheochromocytoma. Hereditary medullary thyroid cancer is inherited as an autosomal dominant trait, meaning that each child of an affected parent has a 50% probability of inheriting the mutant RET proto-oncogene from the affected parent. DNA analysis makes it possible to identify children who carry the mutant gene; surgical removal of the thyroid in children who carry the mutant gene is curative if the entire thyroid gland is removed at an early age, before there is spread of the tumor. The parathyroid tumors and pheochromocytomas are removed when they cause clinical symptomatology. Hereditary medullary thyroid carcinoma or multiple endocrine neoplasia (MEN2) accounts for approximately 25% of all medullary thyroid carcinomas.

Seventy-five percent of medullary thyroid carcinoma occurs in individuals without an identifiable family history and is assigned the term "sporadic". Individuals who develop sporadic medullary thyroid carcinoma tend to be older and have more extensive disease at the time of initial presentation than those with a family history (screening is likely to be initiated at an early age in the hereditary form). Approximately 25-60% of sporadic medullary thyroid carcinomas have a somatic mutation (one that occurs within a single "parafollicular" cell) of the RET proto-oncogene. This mutation is presumed to be the initiating event, although there could be other as yet unidentified causes.

Hurthle cell thyroid cancer is often considered a variant of follicular cell carcinoma. Hurthle cell forms are more likely than follicular carcinomas to be bilateral and multifocal and to metastasize to lymph nodes. Like follicular carcinoma, unilateral hemithyroidectomy is performed for non-invasive disease, and total thyroidectomy for invasive disease.

Thyroid neoplasm is a neoplasm or tumor of the thyroid. It can be a benign tumor such as thyroid adenoma, or it can be a malignant neoplasm (thyroid cancer), such as papillary, follicular, medullary or anaplastic thyroid cancer. Most patients are 25 to 65 years of age when first diagnosed; women are more affected than men. The estimated number of new cases of thyroid cancer in the United States in 2010 is 44,670 compared to only 1,690 deaths. Of all thyroid nodules discovered, only about 5 percent are cancerous, and under 3 percent of those result in fatalities.

Parathyroid carcinoma is sometimes diagnosed during surgery for primary hyperparathyroidism. If the surgeon suspects carcinoma based on severity or invasion of surrounding tissues by a firm parathyroid tumor, aggressive excision is performed, including the thyroid and surrounding tissues as necessary.

Agents such as calcimimetics (for example, cinacalcet) are used to mimic calcium and are able to activate the parathyroid calcium-sensing receptor (making the parathyroid gland "think" we have more calcium than we actually do), therefore lowering the calcium level, in an attempt to decrease the hypercalcemia.

Treatment of a thyroid nodule depends on many things including size of the nodule, age of the patient, the type of thyroid cancer, and whether or not it has spread to other tissues in the body.

If the nodule is benign, patients may receive thyroxine therapy to suppress thyroid-stimulating hormone and should be reevaluated in 6 months. However, if the benign nodule is inhibiting the patient's normal functions of life; such as breathing, speaking, or swallowing, the thyroid may need to be removed.

Sometimes only part of the thyroid is removed in an attempt to avoid causing hypothyroidism. There's still a risk of hypothyroidism though, as the remaining thyroid tissue may not be able to produce enough hormones in the long-run.

If the nodule is malignant or has indeterminate cytologic features, it may require surgery. A thyroidectomy is a medium risk surgery that can result complications if not performed correctly. Problems with the voice, nerve or muscular damage, or bleeding from a lacerated blood vessel are rare but serious complications that may occur. After removing the thyroid, the patient must be supplied with a replacement hormone for the rest of their life. This is commonly a daily oral medication prescribed by their endocrinologist.

Radioactive iodine-131 is used in patients with papillary or follicular thyroid cancer for ablation of residual thyroid tissue after surgery and for the treatment of thyroid cancer. Patients with medullary, anaplastic, and most Hurthle cell cancers do not benefit from this therapy. External irradiation may be used when the cancer is unresectable, when it recurs after resection, or to relieve pain from bone metastasis.

Intake of alcohol during pregnancy has been associated with childhood leukemia. A review published by the National Cancer Institute placed maternal alcohol consumption during pregnancy in the category of "suggestive" but concluded that the risk was not important.

- Acute Lymphocytic Leukemia (ALL)

For ALL in children, maternal alcohol consumption during pregnancy is "unlikely to be an important risk factor for ALL"

- Acute myeloid leukemia (AML)

A study concluded, "In conclusion, even though our study did not show a clear association between alcohol intake and leukemia risk, some of the patterns of the risk estimates (a possible J-shaped dose-response curve between alcohol intake and ALL, AML, and CLL risks, and the positive association between alcohol and CML), may be suggestive."

- Childhood AML

"Three studies have reported an increased risk (approximately 1.5-2 fold) in mothers who drank alcoholic beverages during pregnancy. These associations have been particularly apparent in children diagnosed younger than three years of age.". "Maternal alcohol consumption during pregnancy increases the risk of infant leukemia, especially AML."

- Acute non-lymphocytic leukemia (ANLL)

A study found that intrauterine exposure to alcohol doubled the risk for childhood ANLL.

- Chronic Lymphocytic Leukemia (CLL)

A study concluded, "In conclusion, even though our study did not show a clear association between alcohol intake and leukemia risk, some of the patterns of the risk estimates (a possible J-shaped dose-response curve between alcohol intake and ALL, AML, and CLL risks, and the positive association between alcohol and CML), may be suggestive."

- Chronic myeloid leukemia (CML)

A population-based case-control study in Italy found a non-significant positive association between drinking and CML.

- Hairy cell leukemia

A study concluded, "There was no association found for cigarette smoking, alcohol or coffee consumption and hairy cell leukemia."

Alcohol use is associated with an increased risk of salivary gland cancer.

The Hürthle cell is named after German histologist Karl Hürthle, who investigated thyroid secretory function, particularly in dogs. However, this is a misnomer since Hürthle actually described parafollicular C cells. The cell known as the Hürthle cell was first described in 1898 by Max Askanazy, who noted it in patients with Graves' disease.

A Hürthle cell () or Askanazy cell () is a cell in the thyroid that is often associated with Hashimoto's thyroiditis as well as benign and malignant tumors (Hürthle cell adenoma and Hürthle cell carcinoma, a subtype of follicular thyroid cancer). This version is a relatively rare form of differentiated thyroid cancer, accounting for only 3-10% of all differentiated thyroid cancers. Oncocytes in the thyroid are often called Hürthle cells. Although the terms oncocyte, oxyphilic cell, and Hürthle cell are used interchangeably, Hürthle cell is used only to indicate cells of thyroid follicular origin.

Hürthle cell adenoma is a rare benign tumor, typically seen in women between the ages of 70 and 80 years old. This adenoma is characterized by a mass of benign Hürthle cells (Askanazy cells). Typically such a mass is removed because it is not easy to predict whether it will transform into the malignant counterpart, a subtype of follicular thyroid cancer called a Hürthle cell carcinoma.

Solitary thyroid nodules are more common in females yet more worrisome in males. Other associations with neoplastic nodules are family history of thyroid cancer and prior radiation to the head and neck.

Most common cause of solitary thyroid nodule is benign colloid nodules and second most common cause is follicular adenoma.

Radiation exposure to the head and neck may be for historic indications such as tonsillar and adenoid hypertrophy, "enlarged thymus", acne vulgaris, or current indications such as Hodgkin's lymphoma. Children living near the Chernobyl nuclear power plant during the catastrophe of 1986 have experienced a 60-fold increase in the incidence of thyroid cancer. Thyroid cancer arising in the background of radiation is often multifocal with a high incidence of lymph node metastasis and has a poor prognosis.

Medullary carcinoma may refer to one of several different tumors of epithelial origin. As the term "" is a generic anatomic descriptor for the mid-layer of various organ tissues, a medullary tumor usually arises from the "mid-layer tissues" of the relevant organ.

Medullary carcinoma most commonly refers to:

- Medullary thyroid cancer

- Medullary carcinoma of the breast

Medullary carcinoma may also refer to tumors of:

- Pancreas

- Ampulla of Vater

- Gallbladder

- Stomach

- Large intestine

- Kidney — Renal medullary carcinoma

The overall 5-year survival rate of anaplastic thyroid cancer has been given as 7% or 14%, although the latter has been criticized as being overestimated.

Treatment of anaplastic-type carcinoma is generally palliative in its intent for a disease that is rarely cured and almost always fatal, with worse prognosis associated with large tumours, distant metastases, acute obstructive symptoms, and leukocytosis. Death is attributable to upper airway obstruction and suffocation in half of patients, and to a combination of complications of local and distant disease, or therapy, or both in the remainder.

Anaplastic thyroid cancer is extremely aggressive; in most cases death occurs in less than 1 year as a result of aggressive local growth and compromise of vital structures in the neck. ATC in most series has a median survival of 4 to 5 months from the time of diagnosis, with rare long-term survivors.

Surgery (thyroidectomy) may be indicated in the following instances:

- Reaccumulation of the nodule despite 3–4 repeated FNACs

- Size in excess of 4 cm in some cases

- Compressive symptoms

- Signs of malignancy (vocal cord dysfunction, lymphadenopathy)

- Cytopathology that does not exclude thyroid cancer

There are three main treatments for Hürthle cell adenomas. Once the adenoma is detected most often the nodules removed to prevent the cells from later metastisizing. A total thyroidectomy is often performed, this results in a complete removal of the thyroid. Some patients may only have half of their thyroid removed, this is known as a thyroid lobectomy. Another treatment option includes pharmacological suppression of thyroid hormone. The thyroid gland is responsible for producing the thyroid hormones triiodothyronine (T3) and thyroxine (T4). Patients with suppressed thyroid function often require oral thyroid replacement (e.g. levothyroxine) in order to maintain normal thyroid hormone levels. The final treatment option is RAI abaltion (radioactive iodine ablation). This treatment option is used to destroy infected thyroid cells after total thyroidectomy. This treatment does not change prognosis of disease, but will diminish the recurrence rate. Also, Hürthle cells do not respond well to RAI. However, often doctors suggest this treatment to patients with Hürthle cell adenoma and Hürthle cell carcinoma because some Hürthle cells will respond and it will kill remaining tissue.

An endocrine gland neoplasm is a neoplasm affecting one or more glands of the endocrine system.

Examples include:

- Adrenal tumor

- Pituitary adenoma

The most common form is thyroid cancer.

Condition such as pancreatic cancer or ovarian cancer can be considered endocrine tumors, or classified under other systems.

Pinealoma is often grouped with brain tumors because of its location.

Unlike its differentiated counterparts, anaplastic thyroid cancer is highly unlikely to be curable either by surgery or by any other treatment modality, and is in fact usually unresectable due to its high propensity for invading surrounding tissues.

Palliative treatment consists of radiation therapy usually combined with chemotherapy.

New drugs, such as fosbretabulin (a type of combretastatin), bortezomib and TNF-Related Apoptosis Induced Ligand (TRAIL), are however being under investigation "in vitro" and in human clinical studies. Based on encouraging Phase I and II clinical trial results with fosbretabulin, a type of drug that selectively destroys tumor blood vessels, a large, multi-national clinical trial is being undertaken to determine whether the drug can extend the survival of patients with ATC.

Hyperthyroidism is a state in which the body is producing too much thyroid hormone. The main hyperthyroid conditions are:

- Graves' disease

- Toxic thyroid nodule

- Thyroid storm

- Toxic nodular struma (Plummer's disease)

- Hashitoxicosis: "transient" hyperthyroidism that can occur in Hashimoto's thyroiditis