MYC and neoplasm: In order to determine BFL1 expression levels in the different tumour cell subsets, we FACS‐sorted B220+CD19+ tumour cells and B220−CD19− nontumour cells from the spleen and B220+CD19+ and B220+CD19−CD4+ tumour cells from the thymus of diseased Eμ‐MYC/Vav‐BFL1 DT mice.