MD, FACE
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Thyroid cancer
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Hyperthyroidism
Hypothyroidism
Nodular thyroid disease
Thyroid cancer
Tumor markers are proteins that are produced by tumors and released into the blood and can be monitored as an indicator of the activity and extent of the tumor.
Papillary and Follicular Cancers make up approximately 90-95% of thyroid cancers. Many of these tumors release a protein called thyroglobulin. Thyroglobulin (Tg) is usually produced in normal thyroid cells. Malignant thyroid cells often retain their ability to produce Tg.
Generally, patients will have monitoring of their Tg following surgery to remove the thyroid, and radioactive iodine (RAI) to ablate the thyroid remnant. After about 6 months following RAI therapy, any elevation of Tg is suggestive of residual or recurrent cancer.
Suppressed Tg is measured when the patient is taking appropriate suppressive doses of levothyroxoine. However,the low TSH that results can decrease Tg levels to undetectable levels—even when thyroid cancer cells are still present. The gold-standard test for Tg is done after stimulation of TSH to high levels for at least 48 hours. Now days this is generally done after receiving intramuscular injections of Thyrogen (human TSH) on 2 consecutive days and then measuring Tg 3 days after the 2nd injection. Absence of stimulated Tg levels is a reassuring that there is no residual thyroid cancer. Unfortunatly there can be exceptions to this rule.
Anti-Tg anti-bodies are sometimes present in patients with thyroid cancer (20%) since they may have underling autoimmune disease. These antibodies can prove to be a nuisance in measuring Tg. Significant anti-Tg antibodies decrease our confidence in the measured Tg levels. Thus, Tg levels must be interpreted with caution when the patient is Tg-antibody positive. For this reason, we recommend that anti-Tg antibodies be measured each time the Tg is measured as a way to validate the test and scale your confidence in the result.
A relatively small number of thyroid cancers are medullary thyroid cancers and these tumors produce calcitonin as a useful gage of tumor burden and disease activity. In contrast to Tg, calcitonin is not suppressed by thyroid hormone. CEA is also produced by some medullary thyroid cancers and can be a useful marker of disease activity.
