PAX5 and cancer: Given that RUNX1 also upregulates the expression of Csf1r by binding to its promoter and enhancer regions36 and that the PAX5 deletion alone removes the repression of Csf1r and other myeloid lineage-specific genes and induces the BM B-cell precursor transdifferentiation14,33, we think that RUNX1 supports CSF1R expression in CSF1R+ BMBP to downregulate Pax5 in response tonic and cancer-secreted M-CSF.