Second cancer risk in childhood cancer survivors treated with intensity-modulated radiation therapy (IMRT).

Abstract

Treatment with radiotherapy (RT) is associated with an increased risk of second malignant neoplasms (SMNs) in childhood cancer survivors; it is unclear how treatment with intensity-modulated radiation therapy (IMRT) impacts this risk. We provide the first report of SMN risk in a cohort of childhood cancer survivors treated with IMRT. Retrospective review of patients ≤21 years of age treated with IMRT at Memorial Sloan Kettering Cancer Center between December 1998 and February 2009. Eligible patients survived at least 5 years from IMRT initiation. The risk of SMN was assessed via standardized incidence ratios (SIRs) and excess absolute risk (EAR). The cumulative incidence was estimated using methods for competing risks. Among 242 patients, six developed SMNs: four developed second solid cancers (all within the radiation field), and two developed myelodysplastic syndrome. Median time from IMRT initiation to a second solid cancer was 7.2 years (range, 6.8-9.5), with a 10-year cumulative incidence of 3.3% (95% confidence interval [CI], 1.0-7.8%), SIR of 11.4 (95% CI, 3.1-29.2) and EAR of 1.8 per 1,000 person-years (95% CI, -0.1 to 3.8). Longer follow-up is required to determine how the risk of SMN after IMRT compares to other modalities of radiation treatment, such as proton therapy. This study provides a preliminary report, which will serve as a baseline for future longitudinal analyses of SMN risk after IMRT. Pediatr Blood Cancer 2015;62:311-316. © 2014 Wiley Periodicals, Inc.