ZAP70 and B-cell chronic lymphocytic leukemia: Because both Lck and Zap-70 are physiologically expressed in some B-cell subpopulations [53,54,69,70,71,72], it is still under debate whether Lck and Zap-70 are ectopically expressed in CLL or whether Lck- and Zap-70-positive CLL arise following transformation of B-cell subpopulations normally expressing these molecules.