Researchers associated with the Childhood Cancer Survivor Study have reported that survivors of childhood cancer who had received radiation therapy to the neck had a dose-related increased risk of thyroid cancer. The details of this study appeared in the June 10, 2005 issue of The Lancet .[1]

Radiation is a known carcinogen but is a necessary part of curative therapy for many childhood malignancies. One of the consequences of radiation therapy is secondary malignancy occurring years after radiation therapy. The purpose of the present study was to evaluate the risk of thyroid cancer in children with leukemia, CNS tumor, Hodgkin’s lymphoma, non-Hodgkin’s lymphoma, kidney tumor, neuroblastoma, soft-tissue sarcoma or bone cancer. There were a total of 360 patients; 288 controls and 72 with thyroid cancer. Seventy-eight per cent of these 72 patients had papillary histology. The median interval from treatment to diagnosis of thyroid cancer was 16 years. These authors reported that there was an increasing incidence of thyroid cancer up to a dose of 20-29 Gy. Doses of 30 Gy or greater were associated with a lower incidence of thyroid cancer than lower doses. However, this still represented a greater than three-fold increase in the risk of thyroid cancer compared to controls. The risk of thyroid cancer persisted for up to 30 years in this study. These authors suggest that all survivors of radiation therapy to the head and neck or thorax have annual examinations of the thyroid gland. The authors also suggest that ultrasound is the optimal method for cancer detection. In the accompanying editorial it was also pointed out that patients with secondary thyroid cancer have equivalent outcomes to those with primary thyroid cancer with a survival rate approaching 100%.[2][3]

Comments:  These analyses stress the importance of continued annual evaluation of all survivors of childhood cancer as they are at risk for thyroid and other secondary cancers.

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