Secondary thyroid neoplasms in pediatric cancer patients: increased risk with improved survival.

Between 1973 and 1983, eight children who had undergone successful multimodal management of malignant tumors developed secondary thyroid neoplasms. The primary tumors were acute lymphocytic leukemia in three. Wilms' tumor in two, and Hodgkin's disease, rhabdomyosarcoma, and ganglioneuroblastoma in one each. During this period, 174 long-term survivors with these five diagnoses were enrolled in our tumor registry, yielding a 4.6% incidence of secondary thyroid neoplasms. All eight patients received both radiation and chemotherapy. The mean radiation dose was 2,700 r with a calculated thyroid dose of 2,140 r (range, 5 to 4,200 r). Age of diagnosis of the primary tumors ranged from 1 to 8 2/12 years (mean, 5 years), and the latent period between treatment and development of the thyroid lesions averaged 6 1/2 years. Thyroid neoplasms presented at an average age of 11 4/12 years. Five patients developed solitary adenomas, one presented with multiple adenomas, and two had follicular carcinoma with regional lymph node metastases. Although thyroid neoplasms are rare in childhood, clinically apparent thyroid tumors have been observed in up to 2.5% of children following radiation exposure (mean follow-up, 24 years). The reported latent period before the development of thyroid neoplasms in irradiated patients is at least 10 years, with the peak incidence occurring 20 to 25 years after exposure. This study documents a 4.6% incidence of subsequent thyroid neoplasms in pediatric cancer patients within a relatively short follow-up period (mean, 11 years). These thyroid tumors occurred at an earlier age (mean, 11.5 years) and with a shorter latent period (mean, 6.5 years) than would be predicted from previous studies. These data indicate that multimodal management of pediatric cancer patients utilizing both radiation and chemotherapy increases the risk for the development of secondary thyroid neoplasms. Furthermore, it strongly suggests that the occurrence of these neoplasms will proportionately increase with time, making careful evaluation of the thyroid gland an important component of follow-up care in survivors of childhood malignancies.