Thyroid cancer

Thyroid cancer refers to any of four kinds of tumors of the thyroid gland: papillary, follicular, medullary and anaplastic. Papillary and follicular tumors are the most common: they grow slowly, may recur, but are generally not fatal in patients under 45 years of age. Medullary and anaplastic tumors are malignant. 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 nodule are diagnosed by ultrasound guided fine needle aspiration (USG/FNA) or frequently by thyroidectomy (surgical removal and subsequent histological examination). As the thyroid cancer can uptake iodine, radioactive iodine is a commonly used modality in thyroid carcinomas. However, it is followed by TSH suppression by thyroxine therapy.

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Symptoms

Most often the first symptom of thyroid cancer is a nodule in the thyroid region of the neck. 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. Other 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 hyperthyroidism may be a symptom of a large or metastatic well-differentiated tumor.

Nodules should be of particular concern when they are found in children or 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, or a thyroidologist is the best approach. 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. ^[1]

Fine needle biopsy

One approach used to determine whether the nodule is malignant is the fine needle biopsy (FNB)^[2], which some have described as the most cost-effective, sensitive and accurate test.^{[citation needed]} 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 the 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,^[3] 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 I¹²³ 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.^[4][5] The following variants can be distinguished (distribution over various subtypes may show regional variation):

• Papillary thyroid cancer
• Follicular thyroid cancer
• Medullary thyroid cancer (up to 8%)^[6]
• Anaplastic thyroid cancer
• Others
  • Lymphoma
  • Squamous cell carcinoma, sarcoma

The follicular and papillary types together can be classified as "differentiated thyroid cancer".^[7] These types have a more favorable prognosis than the medullary and undifferentiated types.^[8]

References

See also

• Chernobyl disaster (radioactive contamination is a cause of thyroid cancer)