ALK-positive large B-cell lymphoma (ALK + LBCL) with aberrant CD3 expression.

Area of Science:

• Hematology
• Oncology
• Immunophenotyping

Background:

• Anaplastic lymphoma kinase-positive large B cell lymphoma (ALK+ LBCL) is a rare, aggressive subtype of diffuse large B cell lymphoma.
• This lymphoma typically exhibits negativity for B-cell markers (CD20, CD19, CD22) and positivity for plasmacytic markers (CD138, CD38, MUM1).
• T-cell marker expression is generally absent, with rare exceptions.

Purpose of the Study:

• To report an unusual case of ALK+ LBCL in a 58-year-old male.
• To investigate the diagnostic challenges posed by ambiguous immunophenotypes in ALK+ LBCL.
• To explore the significance of rare T-cell marker expression in this lymphoma subtype.

Main Methods:

• Utilized flow cytometry, immunohistochemistry, and fluorescent in situ hybridization (FISH).
• Performed gene rearrangement studies for IGH and TCR gamma.
• Analyzed tissue sections for specific cellular markers and ALK gene disruption.

Main Results:

• The neoplasm expressed CD45 and plasmacytic markers (CD138, MUM1) with kappa restriction, but lacked typical B-cell markers (CD20, CD79a, PAX5).
• Strong cytoplasmic ALK expression and FISH-confirmed ALK gene disruption were observed.
• Coexisting IGH and TCR gamma gene rearrangements were detected, with the TCR clone appearing polyclonal, suggesting limited T-cell involvement.

Conclusions:

• ALK+ LBCL can present with an ambiguous immunophenotype requiring extensive antibody panels for accurate diagnosis.
• Partial CD3 expression, as seen in this case, is rare in ALK+ LBCL and its clinical significance requires further investigation.
• Comprehensive diagnostic approaches are crucial for correctly identifying and characterizing rare lymphoma subtypes.