FCI of the CSF increased the detection rate of CNS involvement of ALL approximately two times compared to cytomorphology. Patients with low-level CNS involvement may benefit from additional intensified systemic or CNS-directed therapy, but larger studies are needed.

Background Sweden adopted a different strategy than many other countries to combat the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) pandemic and kept most schools open. Initial reports from China suggested that coronavirus disease 2019 (COVID‐19) was milder in children compared to adults, but there was a lack of data from immunocompromised children. Therefore, we investigated the rate of verified SARS‐CoV‐2 infections in our Swedish pediatric oncology patients. Procedure This was a multicenter retrospective study. A questionnaire including patient data as well as SARS‐CoV‐2 data was sent to the six Swedish childhood cancer centers in May 2021. Results During the first pandemic year, 49 patients were identified as SARS‐CoV‐2 positive, and 22 (45%) children were hospitalized with COVID‐19. Two children needed intensive care, but no COVID‐19‐related deaths were reported. Most patients ( n = 36, 73%) were on active chemotherapy treatment and 23 children (49%) attended school or daycare at least part‐time. Half of the SARS‐CoV‐2‐positive patients experienced a delay in cancer treatment. Conclusions Despite the rapid spread of SARS‐CoV‐2 in Sweden, without a strict lockdown of the society, the number of nationally reported pediatric oncology patients with polymerase chain reaction (PCR)‐verified infection was low, and the majority of children had mild disease. Our data show that treatment interruptions occurred frequently and this should clearly be avoided for the coming years.