Bone marrow involvement by marginal zone B-cell lymphomas of different types

Area of Science:

• Hematology
• Oncology
• Pathology

Background:

• Marginal zone B-cell lymphoma (MZL) is a heterogeneous group of B-cell neoplasms.
• Bone marrow (BM) involvement is common in MZL and impacts prognosis.
• Morphologic assessment of BM infiltration patterns is crucial for diagnosis and subtyping.

Purpose of the Study:

• To compare the bone marrow morphologic findings across different MZL subtypes.
• To identify specific patterns indicative of splenic MZL (SMZL), extranodal MZL (MALT lymphoma), and nodal MZL.
• To evaluate the utility of immunohistochemistry in diagnosing MZL in bone marrow.

Main Methods:

• Retrospective analysis of bone marrow biopsy sections from 18 SMZL, 6 extranodal MZL, and 6 nodal MZL cases.
• Evaluation of infiltration patterns including nodular, interstitial, and sinusoidal patterns.
• Immunohistochemical staining for CD21 and CD23 to highlight follicular dendritic cells.

Main Results:

• Median BM involvement was 15% across all MZL types, with nodular and interstitial patterns being most frequent.
• A focal sinusoidal pattern was observed in one third of SMZL cases and rarely in MALT lymphoma.
• Germinal centers were uncommon but observed in SMZL; CD21/CD23 staining highlighted follicular dendritic cells in most cases.
• MZL subtypes showed overlapping BM infiltration patterns, making distinction challenging based on BM morphology alone.

Conclusions:

• Bone marrow morphology alone is insufficient to reliably distinguish between MZL subtypes.
• The presence of a sinusoidal pattern or germinal centers in BM sections is suggestive of SMZL.
• Correlating BM findings with complete blood count (CBC) can improve diagnostic accuracy for SMZL.