Thyroid Cancer Risk Related to Radiotherapy for Childhood Cancer

Radiotherapy used to treat childhood cancers may contribute to survivors developing subsequent thyroid cancer, say researchers from the US NCI in the June 11 journal Lancet. Chemotherapy given for the original cancer had no impact on later thyroid cancer risk, nor did it modify the risk found from radiotherapy.

LIN Note: radiotherapy is often used in childhood lymphoma treatment.

"Childhood cancer survivors with a history of radiation exposure to the chest, neck, or head should be considered at risk for thyroid cancer and these patients should have yearly thyroid and neck examinations," the authors said.

By correlating the dose of cumulative radiation received with the occurrence of secondary thyroid cancer, the researchers found evidence for decline in risk at high doses that earlier studies could not. The risk varies with the radiation that the researchers calculated was absorbed by the patient's thyroid gland at the time of original treatment. From 1 Gy up to 20 Gy, the risk increases, peaking between 20 and 29 Gy. Above 30 Gy and up to 50 Gy the risk decreases, "consistent with a cell-killing effect at high doses," said the authors. The study results do not have implications for clinical treatment decisions with regard to childhood cancers because other serious late effects of radiotherapy and chemotherapy do show increasing risk with increasing doses. NCI Bulletin

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