In summary, we demonstrate that BCR::ABL1 can drive the expansion of murine MCs and that these BCR::ABL1 transformed MCs, as part of the malignant clone, are essential for the disease associated development of splenomegaly and for the elevation of pro-inflammatory cytokines, known to be important in disease initiation and progression. The gene discussed is ABL1; the disease is Splenomegaly.