Children diagnosed with noncentral nervous system solid cancers (NCNSSC) experience several adverse late effects, including second malignant neoplasm. The aim of our study was to assess the risk of specific second malignancies after a childhood NCNSSC. Diagnosis and follow-up data on 10,988 cases of NCNSSC in children (0-14 years) were obtained from 13 registries. Standardized incidence ratios (SIRs) with 95% confidence intervals (CI) and cumulative incidence of second malignancies were computed. We observed 175 second malignant neoplasms, yielding a SIR of 4.6, 95% CI: 3.9-5.3. When considering second cancers with at least 10 occurrences, highest relative risks were found for second malignant bone tumors (SIR = 26.4, 16.6-40.0), soft tissue sarcomas (SIR = 14.1, 6.7-25.8) and myeloid leukemia (SIR = 12.7, 6.3-22.8). Significant increased risks for all malignancies combined were observed after sympathetic nervous system tumors (SIR = 11.4, 5.2-21.6), retinoblastomas (SIR = 7.3, 5.4-9.8), renal tumors (SIR = 5.7, 3.8-8.0), malignant bone tumors (SIR = 5.6, 3.7-8.2), soft tissue sarcomas (SIR = 4.7, 3.2-6.8), germ-cell, trophoblastic and other gonadal neoplasms (SIR = 2.5, 1.1-4.9), carcinomas and other malignant epithelial neoplasms (SIR = 2.2, 1.4-3.3). The highest risk of a second malignancy of any type occurred 5 to 9 years after NCNSSC (SIR = 9.9, 6.8-13.9). The cumulative incidence of second malignancies 10 years after the first neoplasm was eight times higher among NCNSSC survivors than in the general population, with the absolute difference between observed and expected cumulative incidence still increasing after 50 years of follow-up. Children who survived a NCNSSC experience a large increased risk of developing a new malignancy, even many years after their initial diagnosis.
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