Childhood cancer in Sweden during the COVID-19 pandemic: Temporal patterns in incidence and survival in a nationwide register-based cohort study.
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BACKGROUND: The COVID-19 pandemic raised concerns about diagnostic delays and treatment disruptions in childhood cancer, potentially threatening survival. We assessed childhood cancer incidence and survival in Sweden, where only few restrictions were implemented, during the pandemic period. METHODS AND FINDINGS: We conducted a nationwide, register-based cohort study including all children and adolescents (0-19 years) with a new cancer diagnosis, defined according to the International Classification of Childhood Cancer, Third Edition (ICCC-3), reported to the Swedish National Cancer Register during 2015-2022 (N = 3,333; 2,069 pre-pandemic and 1,264 during the pandemic). We compared quarter-specific age-standardized incidence rates (ASR) per 1,000,000 (overall and by diagnostic group) during 2020-2022 to the 2015-2019 average. Overall survival at 3, 6, and 12 months post-diagnosis was calculated using the Kaplan-Meier estimator, and mortality at the same intervals was assessed with logistic regression, adjusted for age at diagnosis, sex, and maternal education. Overall incidence rates remained largely stable during the pandemic (ASR2015-2019: 179.5; 95% CI [172.9,186.1], ASR2020: 174.7; 95% CI [160.5,189.0], ASR2021: 176.5; 95% CI [161.6,191.5], ASR2022: 181.2; 95% CI [166.3,196.2]), but diagnostic groups showed differing tendencies. Acute lymphoblastic leukemia (ALL) declined from February 2020, followed by a rebound in 2021. Acute myeloid leukemia (AML) declined throughout 2020-2022 without evidence of a rebound. Lymphomas declined in mid-2020 before returning to pre-pandemic levels. Central nervous system (CNS) tumors transiently increased in 2020. Overall 1-year survival was 94.8% (95% CI [93.9,95.8]) in the pre-pandemic period and 95.9% (95% CI [94.8,97.0]) during the pandemic. No increase in 6-month or 1-year mortality was observed; if anything, point estimates suggested lower 1-year mortality for ALL (aOR = 0.37; 95% CI [0.08,1.21]; p = 0.14) and CNS tumors (aOR = 0.61; 95% CI [0.31,1.14]; p = 0.13). The main limitation of this study was statistical uncertainty for certain diagnostic groups due to small case numbers. CONCLUSIONS: Overall childhood cancer incidence and survival in Sweden showed no major changes during the COVID-19 pandemic. Fluctuations in diagnostic-group-specific incidence may reflect delayed diagnoses or shifts in disease triggers; however, the timing of the ALL decline and the lack of AML rebound challenge this interpretation. Stable or improved survival suggests that any disruptions were not associated with poorer survival up to 1 year after diagnosis.