Second Malignant Neoplasms Following Treatment for Childhood Cancer: A Population-Based Registry Study

Improved survival after childhood cancer has led to a growing population at risk of second malignant neoplasms (SMNs). This study assessed SMN risk and time trends among childhood cancer survivors in Finland.

Data from the Finnish Cancer Registry included 10 941 patients diagnosed with cancer before age 20 between 1970 and 2020. Patients were followed until 2021 for SMN occurrence (mean follow-up 14.5 years). Standardised incidence ratios (SIRs) and absolute excess risks (AERs) were calculated. Trends were examined by comparing two diagnostic eras: 1970-1990 and 1991-2020.

Among 10 941 patients, 498 (4.6%) developed an SMN. The overall SIR was 4.41 (95% CI 4.03-4.81). Patients diagnosed before age 10 had a significantly higher SMN risk (SIR 6.79, 95% CI 5.92-7.76) than those diagnosed at older ages (SIR 3.47, 95% CI 3.07-3.90; p < 0.001). Survivors of central nervous system (CNS) and solid tumours diagnosed in 1991-2020 had more than twice the SMN risk compared with those diagnosed in 1970-1990.

SMN risk remains significant for childhood cancer survivors, particularly for CNS and solid tumour cases, highlighting the need for tailored surveillance and further research on the strategies to mitigate long-term adverse outcomes.