Objective: The aim of the study was to investigate long-term risk and spectrum of subsequent neoplasm (SN) in childhood cancer survivors and to identify how trends in therapy influenced cumulative incidence of SN.
Materials and methods: The population-based cohort comprises 3271 childhood cancer patients diagnosed in Slovenia aged ⡤ 18 years between 1st January 1961 and 31st December 2013 with a follow-up through 31st December 2018. Main outcome measures are standardized incidence ratios (SIRs), absolute excess risks (AERs), and cumulative incidence of SN. Results: After median follow-up time of 23.2 years, 230 patients experienced 273 SN, including 183 subsequent malignant neoplasm (SMN), 34 meningiomas and 56 nonmelanoma skin cancers. 10.5% patients received radiotherapy only, 31% chemotherapy only, 26.9% a combination of chemotherapy and radiotherapy and 16.1% surgery only. The overall risk for SMN was almost 3 times more than expected (SIR 2.9; 95%CI 2.5-3.3), with survivors still at 2-fold increased risk after attained age 50 years. The observed cumulative incidence of SMN at 30-years after diagnosis was lower for those diagnosed in 1960s, compared with the 1970s and the 1980s (Pheterogeneity<0.001). The observed cumulative incidence of SMN at 40-years after diagnosis was significantly lower for those treated with surgery only compared to chemotherapy and/or radiotherapy (Pheterogeneity<0.001). Despite reduced use of radiotherapy over time, there was no difference in cumulative incidence of SMN 15 years after diagnosis of childhood cancer for patients treated before or after 1995 (Pepe Mori's test, p = 0.11). After attained 40 years of age thyroid, genitourinary, breast, CNS and respiratory tumors were responsible for 80% of the total AER. Compared to general population, childhood cancer survivors had a 6-fold overall increased risk of secondary leukemia (SL). No difference in risk of SL was observed regarding time of diagnosis of childhood cancer. Two thirds of patients developed SL within first 5 years of childhood cancer diagnosis.
Conclusions: Our study reports almost 3-fold increase in SMN among survivors of childhood cancer compared with general population. The SIRs reported by attained age are like other population-based studies. SIR is decreasing with attained age because of a fact that survivors treated long time ago received treatments with minimal carcinogenic potential. With longer follow up time proportion of patients diagnosed with subsequent carcinomas increases. Despite reduced use of radiotherapy after 1995 no difference in cumulative incidence of SMN 15 years after diagnosis of childhood cancer was observed. Risk for SL was greater in our cohort than in other published series due to inclusion of all cases of SL. Risk for SL was not different regardless of time of diagnosis of childhood cancer.
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