Less Misery in Thyroid Cancer Monitoring

The good news about thyroid cancer is that treatment is relatively easy: Surgeons remove the thyroid gland and then administer a dose of radioactive iodine designed to destroy lingering cells. The bad news is that sometimes not all the cells are caught and the yearly monitoring that must follow causes patient anxiety and physical illness; the monitoring also carries a slight risk of accelerating tumor growth. Now a Hopkins study published in the Journal of Clinical Endocrinology and Metabolism suggests a less upsetting way to safely and effectively detect left-over thyroid cells.

The test relies on the discovery that stray human thyroid cells can circulate in the bloodstream. It also expands to patient monitoring a technique, called PCR (polymerase chain reaction), important in gene discovery and cancer diagnosis, “which will likely become standard in the near future,” says endocrinologist Michael Levine, M.D., who led the research team.

Historically, physicians look for remaining thyroid cells either by having patients take radioactive iodine, which concentrates in the thyroid gland and can be detected by scanners, or by analyzing blood for thyroglobulin, a protein made by thyroid cells. Physicians need both methods to pick up leftover thyroid cells that could be cancerous.

But as easy as the tests sound, there’s a catch: Both deliver false results if the blood contains thyroid hormone, standard daily medication for people who have had their thyroid glands removed. Those under treatment and scheduled for monitoring must therefore stop taking their thyroid hormone pills. And the resulting low levels of the hormone, quickly bring on the symptoms of hypothyroidism: depression, fatigue, forgetfulness and intolerance of cold. “Patients become generally miserable for two or three weeks,” Levine says.

The new test solves the problem. Patients can stay on their thyroid medicine. Based on the presence of genes for thyroglobulin, rather than on thyroglobulin itself, the test uses PCR to amplify very low-level gene activity—the sort you’d find with stray cells—to the point where it can be detected. “The technique is extremely sensitive. It can tell, indirectly, if just one or two thyroid cells exist in a teaspoonful of blood,” Levine says.

-—GL