a protein that helps control whether a cell lives or dies by blocking a type of cell death called apoptosis. the gene for the b-cell leukemia/lymphoma 2 protein is found on chromosome 18, and transfer of the b-cell leukemia/lymphoma 2 gene to a different chromosome is seen in many b-cell leukemias and lymphomas. this causes the b-cell leukemia/lymphoma 2 protein to be made in larger amounts, which may keep cancer cells from dying. also called bcl2.