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Thyroid cancer
Classification and external resources
Micrograph (high power view) of papillary thyroid carcinoma demonstrating diagnostic features (nuclear clearing and overlapping nuclei). H&E stain.
ICD-10	C73.
ICD-9	193
eMedicine	ent/646
MeSH	D013964

Thyroid neoplasm or thyroid cancer usually refers to any of four kinds of malignant tumors of the thyroid gland: papillary, follicular, medullary or anaplastic.^[1] Most patients are 25 to 65 years of age when first diagnosed; women are more affected than men.^[1][2] Papillary and follicular tumors are the most common. They grow slowly and may recur, but are generally not fatal in patients under 45 years of age. Medullary tumors have a good prognosis if restricted to the thyroid gland and a poorer prognosis if metastasis occurs. Anaplastic tumors are fast-growing and respond poorly to therapy.

Thyroid nodules are diagnosed by ultrasound guided fine needle aspiration (USG/FNA) or frequently by thyroidectomy (surgical removal and subsequent histological examination). As thyroid cancer can take up iodine, radioactive iodine is commonly used to treat thyroid carcinomas, followed by TSH suppression by high-dose thyroxine therapy.

Symptoms

Micrograph of a lymph node with papillary thyroid carcinoma.

Most often the first symptom of thyroid cancer is a nodule in the thyroid region of the neck.^[1] However, many adults have small nodules in their thyroids, but typically under 5% of these nodules are found to be malignant. Sometimes the first sign is an enlarged lymph node. Later symptoms that can be present are pain in the anterior region of the neck and changes in voice.

Thyroid cancer is usually found in a euthyroid patient, but symptoms of hyperthyroidism or hypothyroidism may be associated with a large or metastatic well-differentiated tumor.

Nodules are of particular concern when they are found in those under the age of 20. The presentation of benign nodules at this age is less likely, and thus the potential for malignancy is far greater.

Diagnosis

After a nodule is found during a physical examination, a referral to an endocrinologist, a thyroidologist or otolaryngologist may occur. Most commonly an ultrasound is performed to confirm the presence of a nodule, and assess the status of the whole gland. Measurement of thyroid stimulating hormone and anti-thyroid antibodies will help decide if there is a functional thyroid disease such as Hashimoto's thyroiditis present, a known cause of a benign nodular goiter.^[3]

Fine needle biopsy

One approach used to determine whether the nodule is malignant is the fine needle biopsy (FNB)^[4], which some have described as the most cost-effective, sensitive and accurate test. ^[5]

^[6] FNB or ultrasound-guided FNA usually yields sufficient thyroid cells to assess the risk of malignancy, although in some cases, the suspected nodule may need to be removed surgically for pathological examination.

Rarely, a biopsy is done using a large cutting needle, so that a piece of nodule capsule can be obtained.

Blood tests

Blood or imaging tests may be done prior to or in lieu of a biopsy. The possibility of a nodule which secretes thyroid hormone (which is less likely to be cancer) or hypothyroidism is investigated by measuring thyroid stimulating hormone (TSH), and the thyroid hormones thyroxine (T4) and triiodothyronine (T3).

Tests for serum thyroid autoantibodies are sometimes done as these may indicate autoimmune thyroid disease (which can mimic nodular disease).

Imaging

The blood assays may be accompanied by ultrasound imaging of the nodule to determine the position, size and texture, and to assess whether the nodule may be cystic (fluid filled). Also suspicious findings in a nodule are hypoechoic,^[7] irregular borders, microcalcifications, or very high levels of blood flow within the nodule. Less suspicious findings in benign nodules include, hyperechoic, comet tail artifacts from colloid, no blood flow in the nodule and a halo, or smooth border.

Some clinicians will also request technetium (Tc) or radioactive iodine (I) imaging of the thyroid. An ¹²³I scan showing a hot nodule, accompanied by a lower than normal TSH, is strong evidence that the nodule is not cancerous.

Classification

Thyroid cancers can be classified according to their pathological characteristics. ^[8][9] The following variants can be distinguished (distribution over various subtypes may show regional variation):

• Papillary thyroid cancer Up to 75% - often in young females - excellent prognosis
• Follicular thyroid cancer Up to 15%
• Medullary thyroid cancer (Up to 8%)- cancer of the parafollicular cells, part of MEN-2.^[10]
• Anaplastic thyroid cancer Less than 5%. It is not responsive to treatment and can cause pressure symptoms.
• Others
  • Lymphoma
  • Squamous cell carcinoma, sarcoma

The follicular and papillary types together can be classified as "differentiated thyroid cancer".^[11] These types have a more favorable prognosis than the medullary and undifferentiated types.^[12]

• Papillary microcarcinoma is a subset of papillary thyroid cancer defined as measuring less than or equal to 1 cm.^[13]. The highest incidence of papillary thyroid microcarcinoma in autopsy series was reported by Harach et al. in 1985, who found 36 of 101 consecutive autopsies were found to have an incidental microcarcinoma ^[14]. Michael Pakdaman et al. report the highest incidence in a retrospective surgical series at 49.9% of 860 cases ^[15]. Management strategies for incidental papillary microcarcinoma on ultrasound (and confirmed on FNAB) range from total thyroidectomy with radioactive iodine ablation to observation alone. Harach et al. suggest using the term "occult papillary tumor" to avoid giving patients distress over having cancer.It was Woolner et al. who first arbitrarily coined the term "occult papillary carcinoma" in 1960, to describe papillary carcinomas ≤ 1.5 cm in diameter.^[16]

Thyroid adenoma is a benign neoplasm of the thyroid.

Etiology

From the 1940s to 1960s, external, low-dose radiation to the head and neck during infancy and childhood was used to treat many benign diseases. This type of therapy has been shown to predispose persons to thyroid cancer. The younger the patient was at time of exposure, the higher the risk of developing cancer.^[1]

Another cause may be due to high-dose irradiation to the head and neck. Patients with Hodgkin lymphoma treated with mantlefield irradiation have an increased risk of developing thyroid cancer, although hypothyroidism is more likely.^[1]

Treatment

If the nodule is benign, patients may receive thyroxine therapy to suppress thyroid-stimulating hormone and should be reevaluated in 6 months.^[1]

If the nodule is malignant or has indeterminate cytologic features, it may require surgery. Common surgeries include thyroidectomy, lobectomy, and tracheostomy.^[1]

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.^[1]

External irradiation may be used when the cancer is unresectable, when it recurs after resection, or to relieve pain from bone metastasis.^[1]

See also

• Radioactive contamination (one of the possible causes of thyroid cancer)
• Papillary thyroid cancer

References

External links

Wikimedia Commons has media related to: Thyroid cancer

• Thyroid cancer at the Open Directory Project
• Thyroid Cancer Clinical Trials Page of the American Thyroid Association
• Nuclear Medicine Information =– Thyroid Diseases
• Thyroid Cancer- National Cancer Institute
• Thyroid Cancer Survivors' Association
• Diagnostic patient information
• The THANC (Thyroid, Head and Neck Cancer) Foundation
• Cancer Management Handbook: Thyroid and Parathyroid Cancers