MYC and lymphoma: Consistent with the Western blot results, PCR analysis of FACS-sorted primary lymphoma cells confirmed that some of the lymphoma cells arising in Eμ-Myc;CD19-Cre;Mcl-1fl/+ and Eμ-Myc;CD19-Cre;Mcl-1fl/fl mice had not excised or only partially excised their Mcl-1fl alleles (Figure 2b).