Second thyroid neoplasms after prophylactic cranial irradiation for acute lymphoblastic leukemia

An understanding of the pathogenesis of second cancers may help in their prevention. We report on two children who were treated for acute lymphoblastic leukemia (ALL), with an exclusively cranial prophylactic irradiation (18 Gy) and who presented with a thyroid carcinoma (TC) 12 and 13 years later. From a thorough review of the literature of TC after ALL and of radiation-induced TC, a strong case can be made that these tumors are caused by late effects of scattered radiation. The risk is at its highest in small children. After cranial irradiation, patients require clinical monitoring of the thyroid and cervical area for nodules, continued indefinitely. We suggest that, in most cases, an alternative form of neuromeningeal prophylaxis should be offered in small children with ALL.