Chronic lymphocytic leukemia - Peripheral blood
Peripheral blood smear shows prominent lymphocytosis. Some smudge cells (arrows) can be identified. The atypical lymphocytes show both small forms with clumped nuclear chromatin as well as some larger forms with more abundant cytoplasm.
The characteristic CLL cell is small with a round nucleus, scant cytoplasm, clumped nuclear chromatin, and inconspicuous nucleoli. The chromatin can appear like “cracked-earth” on smears and “chocolate-chip cookie” or “soccer ball”-like in tissue sections. Prolymphocytes are larger cells with a more visible nucleolus that can be observed in peripheral blood and tissue section. Often in tissue sections, larger cells with a central eosinophilic nucleolus can be seen, consistent with immunoblasts.
Chronic lymphocytic leukemia - Bone marrow
The bone marrow exhibits increased atypical lymphocytes with similar cytologic features as those seen in the peripheral blood (A). These are present in a diffuse pattern (B) infiltrating between normal hematopoiesis (C).
Chronic lymphocytic leukemia - IHC
Immunohistochemical stains show the lymphocytes are mostly CD20-positive B-cells with just a few background T-cells. There is aberrant expression of CD5, without cyclin D1 positivity.
Chronic lymphocytic leukemia - Flow cytometry
Flow cytometry shows a population of CD19+ cells with aberrant CD5 co-expression (black arrow). These have dim kappa expression (red arrow), dim CD20 expression (curved arrow), and positivity for CD23 (yellow arrow) and CD200 (green circle). CD10 and CD79b are both negative.
CLL Flow: CLL/SLL shows a characteristic immunophenotype. The B-cells show reduced expression of surface immunoglobulin and associated antigens, such as lights chains (kappa or lambda), CD20 and CD79b. Most cases are positive for CD200 by flow cytometry and LEF1 by immunohistochemical stain; CD23 is also often positive, but is not entirely sensitive or specific for CLL. There is aberrant co-expression of CD5, which is also seen in mantle cell lymphoma. However, cyclin D1 and the t(11;14) translocation are consistently negative.
Chronic lymphocytic leukemia - Cytogenetics
Conventional karyotype shows trisomy 12 (arrow). FISH studies (not pictured) showed deletion of 13q14.
The karyotype is simple without any other major alterations.