BCR and cancer: An example of the accumulation of a protein distributed between both compartments in normal cells, but enriched in the cytoplasm in cancer cells, is the proto oncogene Bcr-Abl, a ~200 kDa protein resulting from a fusion of parts of the ABL1 (Abelson Murine Leukemia Viral Oncogene Homolog 1) and BCR (breakpoint cluster region) genes.