Relapse and survival after relapse among children with cancer in Denmark: 2001–2021

Background In recent decades, new first and subsequent lines of anticancer treatment and supportive care have improved survival for children with cancer. We investigated recent temporal changes in the incidence of relapse and survival after relapse among children with cancer in Denmark. Procedure This register‐based study included 2890 children diagnosed before age 15 years with haematological cancers and solid tumours (2001–2021) and central nervous system (CNS) tumours (2010–2021). We used the Aalen–Johansen and Kaplan–Meier estimators to assess cumulative incidence of relapse—defined as cancer recurrence or progression—and survival probability after relapse. Results Comparing the periods 2001–2010 and 2011–2021, the 5‐year cumulative incidence of relapse decreased from 14% to 11% among children with haematological cancers (p = .07), and from 21% to 18% among children with solid tumours (p = .26). Concurrently, the 5‐year survival after relapse increased among children with haematological cancers (from 44% to 61%, p = .03) and solid tumours (from 38% to 46%, p = .25). Among children with malignant CNS tumours, the 5‐year cumulative incidence of relapse and the 5‐year survival after relapse remained stable (49% and 51%, p = .82; and 20% and 18%, p = .90) comparing 2010–2015 and 2016–2021. Conclusions In recent decades in Denmark, improvements were observed in reducing relapse incidence and increasing survival after relapse in children with haematological cancers and solid tumours. However, the persistent survival gap between children who relapse and those who do not across all childhood cancers underlines the need for intensified and highly targeted treatments for children at high risk of relapse.