ZAP70 and B-cell chronic lymphocytic leukemia: Contrary to its earlier description as a relatively homogeneous disease, CLL more recently has been viewed as a heterogeneous disease with variable clinical course that correlates with several biologic markers of prognosis [1] The most clinically significant prognostic markers are cytogenetics determined by fluorescence in situ hybridization (FISH) and IgVH followed by ZAP70 status.