BCR and leukemia: When the expression of tnFGFR1 was examined in bone marrow cells following serial transplantation of leukemias driven by BCR-FGFR1 (Fig. 3A) and ZMYM2-FGFR1 (Fig. 3B), the primary leukemia cells showed a predominant expression of the full-length kinase, with relatively low levels of tnFGFR1.