Atypical Chronic Lymphocytic Leukemia-The Current Status.

Area of Science:

• Hematology
• Oncology
• Immunology

Background:

• Typical chronic lymphocytic leukemia (CLL) diagnosis involves specific B-lymphocyte counts and surface antigen expression (CD19, CD20, CD5, CD23).
• Atypical CLL (aCLL) is distinguished by morphological and immunophenotypic variations, often lacking certain surface antigens like CD5 and CD23.
• Current diagnostic approaches for aCLL lean towards immunophenotypic analysis over morphological assessment.

Purpose of the Study:

• To review and summarize current knowledge on the morphological, immunophenotypic, and genetic characteristics of atypical CLL.
• To highlight the diagnostic challenges and ongoing debate surrounding the clinical significance of aCLL.
• To provide an overview of the features that differentiate aCLL from classic CLL.

Main Methods:

• Review of existing literature on chronic lymphocytic leukemia (CLL) and atypical CLL (aCLL).
• Analysis of morphological criteria used to define aCLL, including cell size, form, and presence of prolymphocytes.
• Examination of immunophenotypic differences, focusing on surface antigen expression (e.g., CD5, CD23) and light chain restriction.
• Investigation of genetic abnormalities associated with aCLL, such as trisomy 12 and unmutated IGVH.

Main Results:

• Atypical CLL cells may exhibit large, atypical forms, prolymphocytes, or cleaved cells, but diagnosis often relies on immunophenotype.
• Immunophenotypically, aCLL typically shows reduced or absent expression of one or fewer antigens, commonly CD5 and CD23.
• Patients with aCLL are more prone to aggressive disease markers like trisomy 12, unmutated IGVH, and CD38 expression, indicating a worse prognosis.
• No universally accepted criteria exist for aCLL diagnosis, and its clinical significance is still under investigation.

Conclusions:

• Atypical CLL exhibits distinct morphological and immunophenotypic profiles compared to typical CLL.
• The prognostic implications of aCLL, including its association with aggressive markers, warrant further investigation.
• Standardized diagnostic criteria are needed to clarify the clinical significance and management of atypical CLL.