The pros and cons of thyroglobulin, calcitonin and thyroid cancer...

Author: Cui Wei, Researcher at the Cancer Hospital of the Chinese Academy of Medical Sciences

Reviewer: Xing Xiaoyan, Chief Physician, China-Japan Friendship Hospital

Thyroid cancer is a very common malignant tumor, and its incidence has been increasing in recent years.

Pathologically speaking, thyroid cancer is divided into three categories: differentiated thyroid cancer, medullary carcinoma, and anaplastic carcinoma.

Among them, the most common type is differentiated thyroid cancer, which can account for about 85% or even 90%, and its prognosis is also the best. Undifferentiated cancer has the worst prognosis, but this type is very common.

1. What are the serum markers for thyroid cancer?

According to the guidelines for thyroid cancer, two serum markers are generally recommended: thyroglobulin (Tg) and calcitonin (Ctn). Thyroglobulin is mainly a tumor marker for differentiated thyroid cancer, while calcitonin is mainly a tumor marker for medullary thyroid cancer.

However, because the current detection methods of thyroglobulin indicators may be interfered with by thyroglobulin antibodies, sometimes when testing thyroglobulin, another marker, thyroglobulin antibodies, will be tested together.

In the case of medullary carcinoma, calcitonin was used clinically a little later. Before that, there was another marker called carcinoembryonic antigen (CEA), which is also used more frequently in medullary thyroid carcinoma, and there is relatively more data in this regard. Therefore, for medullary carcinoma, CEA and calcitonin are usually used to make judgments.

As for undifferentiated carcinoma, there is currently no specific tumor marker available for detection.

2. What is thyroglobulin?

Thyroglobulin is a protein produced by thyroid follicular epithelial cells. These follicular epithelial cells can be normal follicular epithelial cells, that is, normal thyroid cells, or they can be diseased thyroid cells, such as tumor cells.

Therefore, thyroglobulin is relatively specific to the thyroid gland itself.

Under normal circumstances, the thyroglobulin content in the human body is very low, usually a nanogram-level indicator, generally 3.5-77 ng/ml, or not more than 80 ng/ml.

If thyroglobulin is elevated, there must be something wrong with the thyroid gland. If it is significantly elevated, it is generally related to differentiated thyroid cancer. If it is slightly elevated, it may also be caused by inflammation of the thyroid gland itself, or by diseases such as hyperthyroidism and goiter.

Figure 1 Original copyright image, no permission to reprint

Sometimes, the thyroglobulin index is very low and cannot be measured. This may be the case for patients who have undergone thyroid surgery and whose thyroid glands have been removed, in which case thyroglobulin may not be measured. It may also be the case that taking some medications, such as thyroxine, can inhibit the secretion of pituitary TSH, thereby inhibiting tumor growth, accompanied by a decrease in thyroglobulin secretion.

3. What is calcitonin?

Calcitonin is a single-chain peptide hormone produced by the parafollicular cells of the thyroid gland. Under normal circumstances, the level of calcitonin in the body is very low, about 10 picograms/ml or less for men and about 7 picograms/ml or less for women.

However, this value is only the result measured by a certain detection system. Because the results detected by different detection systems may be inconsistent, its normal value may also fluctuate.

Elevated calcitonin test values ​​are common in several situations:

Some benign diseases can cause elevated calcitonin levels, such as kidney disease and some pancreatic diseases.

Another is the increase of calcitonin caused by malignant diseases. Because it is also produced by the parafollicular cells of the thyroid gland, this disease is often medullary thyroid cancer, and the most important tumor marker of medullary cancer is calcitonin.

Figure 2 Original copyright image, no permission to reprint

In addition, the increase in calcitonin can also indicate the extent of metastasis of cervical lymph nodes in medullary carcinoma.

Generally speaking, if the calcitonin level is only higher than 50 pg/ml, it may be metastatic to the ipsilateral lymph nodes. If the calcitonin level is higher than 200 pg/ml, it may have metastasized to the contralateral lymph nodes. If the calcitonin level is higher than 500 pg/ml, it may have metastasized to the contralateral side or to the upper mediastinum.