Infection can trigger leukaemia in genetically susceptible mice, suggesting an environmental cause for the most common type of childhood cancer.

Children with precursor B-cell acute lymphoblastic leukaemia often have mutations in the PAX5 gene, which is involved in immune-cell development, but the mutations alone do not cause the disease. To see whether infection might be the trigger, Arndt Borkhardt at the University of Düsseldorf in Germany, Isidro Sanchez-Garcia at the University of Salamanca in Spain and their colleagues exposed mice with Pax5 mutations to common pathogens. The mice developed cancer, whereas Pax5 mutant mice kept in a sterile environment did not.

By sequencing tumour DNA from the diseased mice, the team found extra mutations — probably caused by infection — in genes encoding signalling proteins that help to regulate cell growth. Treating mice with molecules that inhibit these proteins lowered the number of cancer cells, suggesting a new avenue for treatment.

Cancer Discov. http://doi.org/73j (2015)