A blood test for thyroid cancer can detect persistent or recurrent disease even before doctors can find any trace of a tumor, according to a new study. The findings suggest that people treated for the disease should be examined regularly for early signs of recurrence.
The study, by researchers at The Ohio State University Comprehensive Cancer Center – Arthur G. James Cancer Hospital and Richard J. Solove Research Institute (OSU CCC – James), examined how well a test for thyroid cancer can predict whether the disease will recur.
The findings were published June 21 online in the Journal of Clinical Endocrinology & Metabolism.
The test measures a protein known as thyroglobulin (Tg), which is made by thyroid-cancer cells. The measurement is taken after a person is injected with a relatively new drug known as thyrotropin alfa, or Thyrogen. The drug allows Tg testing without the sometimes debilitating side effects of hypothyroidism that otherwise accompany the test when stimulation testing is done.
"We were surprised to find that even with relatively low thyroglobulin levels, and even when there is no sign of a tumor, about 80 percent of patients had a recurrence of their cancer within three to five years," says first author Richard T. Kloos, associate professor of internal medicine and of radiology.
"This indicates that we are detecting these tumors very early, and that time and diligence may be needed to find them."
The study also found that even when Tg levels are very low or undetectable, about 2 to 5 percent of patients still have a recurrence after three to five years.
"Currently, some thyroid-cancer treatment guidelines say that these patients may never need further testing, but our data contradict that," says Kloos, co-director of the Thyroid Cancer Unit at the OSU CCC – James.
Thyroid cancer is usually treated surgically by removing the thyroid gland, followed by drinking radioactive iodine to kill any remaining cancer cells. Patients must then take synthetic thyroid hormone for life.
With all thyroid cells eliminated, the Tg level should be zero, and its presence later signals a possible return of the disease. (Sometimes, however, low levels of Tg can be present following treatment, and slowly decline over time.)
In the past, Tg testing required that patients stop taking their synthetic thyroid hormone several weeks before the test.
"That worked fairly well, except that some people became miserable after they stopped taking their synthetic thyroid hormone and became hypothyroid," Kloos says. "Some patients claimed that they'd rather die of their disease than go through that regularly."