Childhood cancer survivors are 18 times more likely to develop thyroid cancer than the general population, UK researchers report.

“Survival after childhood cancer has greatly improved over the last three decades with 5-year survival 75 percent during the 1990s compared to 25 percent during the 1960s in the United Kingdom,” Dr. Aliki J. Taylor, of the University of Birmingham, and colleagues note in the latest issue of the International Journal of Cancer.

Childhood cancer survivors are at an increased risk of “late effects” of treatment, including the development of second cancers.

To assess the risk of developing thyroid cancer, the researchers analyzed data from 17,980 patients who were enrolled in The British Childhood Cancer Survivor Study and had survived at least 5 years after diagnosis with a childhood cancer from 1940 to 1991.

During a median follow-up of 17.4 years per survivor, 50 cases of thyroid cancer were identified, compared to 2.8 expected in the general population.

Forty-four patients (88 percent) who developed thyroid cancer had received radiation therapy in or around the thyroid gland.

Patients treated radiation therapy for childhood cancer had a greater than fourfold increased risk of developing thyroid cancer, the researchers found.

“These results will be of use in counseling survivors of childhood cancer exposed to radiation in or around the thyroid area,” Taylor and colleagues conclude.

SOURCE: International Journal of Cancer, November 15, 2009.