Aberrant Cluster of Differentiation (CD) Marker Expression Across B-cell Chronic Lymphoproliferative Disorder Subtypes: A Single-Center Flow Cytometry Study From Sri Lanka

Introduction Flow-cytometric immunophenotyping is central to the diagnosis and subclassification of B-cell chronic lymphoproliferative disorders (B-CLPDs). In routine practice, partial antigen loss, reduced expression, and unexpected antigen acquisition may create diagnostic difficulty, particularly when tissue-based or molecular confirmation is delayed. This study describes subtype-wise aberrant cluster of differentiation (CD) marker expression patterns in B-CLPDs diagnosed by integrated morphology and multiparameter flow cytometry in a Sri Lankan tertiary-care laboratory. Methods A descriptive cross-sectional analysis was performed on 210 diagnosed B-CLPD cases. Aberrancies were categorized as unexpected expression, antigen loss, or reduced expression using predefined subtype-specific expectations, internal reference populations, and routine laboratory fluorescence-intensity interpretation. Frequencies were reported as N (%) within each subtype, with denominators specified where relevant. Because several rare subtypes had small numbers, inferential testing was restricted to selected comparable aberrancy events between chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL). Results CLL was the commonest subtype, comprising 94 (44.8%) cases, followed by MCL with 34 (16.2%) and the CD5-negative/CD10-negative/hairy-marker-negative B-CLPD group with 31 (14.8%). In CLL, the most frequent events were unexpected CD20 expression in 44 (46.8%) cases, reduced CD45 in 42 (44.7%), unexpected surface kappa expression in 24 (25.5%), and reduced CD23 in 24 (25.5%). MCL showed reduced CD45 in 11 (32.4%) cases, reduced CD43 in eight (23.5%), reduced CD5 in four (11.7%), unexpected CD23 in four (11.8%), unexpected CD200 in four (11.8%), and reduced FMC7 in four (11.8%). The CD5-negative/CD10-negative/hairy-marker-negative B-CLPD group was the most heterogeneous, with reduced CD200 and reduced FMC7 each occurring in 15 (48.3%) cases. Conclusion CLL was characterized mainly by unexpected CD20 expression and reduced CD45, whereas MCL most commonly showed reduced CD45 and CD43. The CD5-negative/CD10-negative/hairy-marker-negative B-CLPD group showed the greatest immunophenotypic heterogeneity, particularly reduced CD200 and FMC7. These findings demonstrate that aberrant antigen expression is subtype-associated and should be interpreted within the complete immunophenotypic profile rather than using individual markers in isolation.