BCL2 and leukemia: Antiapoptotic members of the Bcl-2 family such as Bcl-2 (B cell leukemia or lymphoma gene number 2), Bcl-xL (B cell lymphoma-extra large), or Mcl-1 (myeloid cell leukemia sequence 1) have first been identified in leukemia and lymphoma and are also frequently overexpressed in other types of neoplasia to inhibit apoptotic cell death during tumorigenesis.