"We found that germline predisposition to childhood leukemia is relatively uncommon, but when present, it can have major implications for the individual child," Nordgren said.

How did the results change care?

The findings had direct clinical consequences. Once the inherited risk variants were identified:

• Eight of the nine children were enrolled in specialized surveillance programs
• Four received modifications to their cancer treatment
• In six of the nine cases, the increased cancer risk had not been recognized before the leukemia diagnosis

"Our results show that genetic testing can provide clinically important information that influences both treatment and follow-up. At the same time, the benefits need to be weighed against available resources and the need for genetic counseling," said Bianca Tesi, consultant clinical geneticist at the Department of Clinical Genetics and Genomics at Karolinska University Hospital and co-senior author of the study.

Why was the rate lower than earlier estimates?

Previous research has estimated that between 4% and 10% of children with blood cancers carry an inherited cancer predisposition. The reported frequencies vary depending on study design and which patients researchers selected.

The new study's rate of about 5% sits at the lower end of that range. The researchers believe this is partly because they included every child in the cohort regardless of whether doctors had any prior suspicion of a hereditary cancer risk — an approach that avoids inflating the numbers by only testing children with suspicious family histories.

"By sequencing every child and combining comprehensive clinical evaluation with whole-genome sequencing and tumor analysis, we obtained a complete picture of how common germline variants are and which genes are involved," said Fulya Taylan, associate professor at the Department of Molecular Medicine and Surgery at Karolinska Institutet and first author of the study.

What are the study's limitations?

The researchers are candid about what the study could not capture. The analyses focused on a predefined list of genes, meaning some genetic causes of leukemia may have been missed. Larger studies are also needed to better understand how much inherited genetic factors contribute to childhood leukemia overall.

The 181-child sample, while prospectively recruited nationwide, remains modest by genomic standards, so the 5% figure carries some statistical uncertainty.

Who carried out the research?

Scientists at six Swedish university hospitals conducted the study in collaboration with research groups within Genomic Medicine Sweden, a national infrastructure for precision medicine. The findings appear in Nature Communications (2026), under the title "Diagnostic yield of cancer predisposition in a nationwide prospective childhood acute leukemia cohort" (DOI: 10.1038/s41467-026-78170-z).

For families of children with leukemia, the takeaway is measured rather than revolutionary: inherited risk is uncommon, but when testing finds it, that knowledge can steer both the choice of therapy and the intensity of monitoring for years afterward.