What Is a Tumor Marker in Thyroid Cancer?
Treatment for most thyroid cancers involves removal of the thyroid gland (thyroidectomy), often followed by radioactive iodine to destroy any remaining thyroid tissue.
Thyroglobulin is a protein produced only by the thryoid gland. After total thyroidectomy and remnant ablation, thyroglobulin (Tg) should thus be virtually undetectable in the bloodstream. Rising levels of Tg post-treatment provide a generally reliable marker for recurrent papillary or follicular thyroid cancer in the absence of remaining healthy thyroid tissue.
Follow-Up
Well-differentiated thyroid cancers (papillary and follicular types) make up approximately 90 percent of all diagnosed cases of thyroid carcinoma. These tumors typically grow slowly and respond well to targeted therapies, and the prognosis for the majority of patients is excellent.
While recurrences are usually highly treatable, diligent follow-up is required for life, as thyroid cancer may reappear decades after initial treatment.
Ablation
A "total" thyroidectomy typically leaves behind a remnant of thyroid tissue. Therefore, radioactive iodine, attracted uniquely to thyroid cells, is then administered orally after surgery to destroy this remnant tissue. Besides decreasing the chances of recurrence, this treatment has the benefit of making thyroglobulin an excellent tumor marker. If any thyroid tissue remains, however, Tg measurement has little prognostic value.
Antibodies
Automimmune thyroid disease (Hashimoto's thyroiditis) is common in patients with thyroid cancer and often causes the body to produce antibodies to thyroglobulin, which render Tg screening unreliable.
Fortunately, following thyroidectomy, the body gradually stops producing these antibodies in most cases. Thus Tg can be a useful tumor marker even in patients with autoimmune thyroid disease.
Tg testing should always be done in conjunction with screening for antibodies, as a return of antibodies may also signify a return of the cancer.
Low thyroglobulin levels immediately following ablation are considered a positive prognostic factor.
TSH
Thyroid-stimulating hormone (TSH) is produced by the pituitary gland to regulate the thyroid's production of hormones. Following thyroidectomy, thyroid hormone replacement is given in pill form and TSH levels are deliberately kept very low (suppressed) to avoid stimulating growth of thyroid cancer cells.
Temporarily raising TSH to unnaturally high levels is the first step in screening for recurrent thyroid cancer. The standard protocol used to involve weeks of what many patients referred to as "hypothyroid hell," in which thyroid hormone replacement was withheld, resulting in unpleasant symptoms such as extreme fatigue, irritability and weight gain.
The availability of injectable recombinant TSH has greatly simplified the process of scanning and Tg measurement for thyroid cancer patients, allowing them to continue thyroid hormone replacement without interruption or significant side effects.
Advances
Recent studies have shown the Tg blood test to be an effective barometer for thyroid cancer recurrence in moderately low-risk patients. A simple blood test, performed periodically in conjunction with injectable TSH, has thus supplanted regular radioactive iodine scanning in many survivors, obviating the need for the low-iodine diet and "hypo hell."
Tags: thyroid cancer, thyroid tissue, hormone replacement, radioactive iodine, , thyroid hormone replacement, blood test