CD5-negative blastoid variant mantle cell lymphoma: a diagnostic dilemma

Area of Science:

• Hematology
• Oncology
• Pathology

Background:

• Mantle cell lymphoma (MCL) is typically CD5-positive, but CD5-negative variants exist.
• Aggressive variants of MCL, such as blastoid and pleomorphic types, present diagnostic challenges.
• Accurate diagnosis is critical due to therapeutic implications.

Purpose of the Study:

• To determine the frequency of CD5 negativity in MCL, including aggressive variants.
• To assess the diagnostic accuracy of MCL variants, particularly CD5-negative cases.
• To evaluate the potential misclassification of CD5-negative MCL variants within diffuse large B-cell lymphoma (DLBCL) diagnoses.

Main Methods:

• Retrospective analysis of 117 MCL cases and 1534 DLBCL cases.
• Immunohistochemical staining for CD5 and cyclin D1.
• Fluorescence in situ hybridization (FISH) for IGH/CCND1 fusion.
• Morphological assessment of tumor cells.

Main Results:

• CD5 negativity was observed in 13% of classical MCL and 15% of blastoid/pleomorphic MCL variants.
• A small proportion (0.9%) of CD5-positive DLBCL cases were reclassified as pleomorphic MCL.
• Two cases initially diagnosed as CD5-negative DLBCL were reclassified as CD5-negative blastoid MCL upon relapse.

Conclusions:

• CD5 negativity occurs in both classical and aggressive MCL variants at similar rates.
• Accurate diagnosis of CD5-negative aggressive MCL variants is challenging and may lead to misdiagnosis.
• CD5-negative aggressive MCL variants can be misidentified as CD5-negative DLBCL, underscoring the need for careful diagnostic evaluation.