Analyses of cell signals provide insight into the origin of severe inflammatory symptoms that appear in various types of blood cancer and point to possible therapeutic approaches: In around one-fourth of patients suffering from juvenile myelomonocytic leukemia (JMML), there is evidence of mutations in the so-called KRAS gene in the leukemia cells. Patients affected by JMML carrying these mutations suffer particularly often from signs of inflammation, such as fever, weight loss, and an abnormal enlargement of the spleen. It was previously unknown how the sometimes severe inflammatory symptoms are connected with the cancer.