Immunohistochemistry for LEF1 and SOX11 adds diagnostic specificity in small B-cell lymphomas

Lymphocyte enhancer–binding factor 1 (LEF1) and SRY-Box 11 (SOX11) are highly sensitive and specific for chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL) and mantle cell lymphoma (MCL) including the cyclin D1–negative subtype, respectively. We assessed the utility of these markers in a large cohort of small B-cell lymphomas (SBCLs) on varied sample types. Immunohistochemistry (IHC) was performed for LEF1 and SOX11 on 354 SBCLs (129 CLL/SLLs, 33 MCLs, 142 marginal zone lymphomas [MZLs]—nodal MZL [NMZL]: 40, extranodal MZL [ENMZL]: 28, splenic MZL [SMZL]: 74 cases—and 50 lymphoplasmacytic lymphomas [LPLs]/Waldenstrom macroglobulinemias [WMs]). Ninety-eight percent of CLL/SLLs were LEF1 positive. SOX11 showed good sensitivity (82%) and excellent specificity for MCL (99%), with only 2 of 142 MZLs (both SMZLs) showing SOX11 expression. The low sensitivity for SOX11 was on account of inclusion of 4 non-nodal cases. All 50 LPL/WMs were negative for both LEF1 and SOX11. The expression of SOX11 and LEF1 was not always mutually exclusive, as 2 confirmed MCLs expressed both markers. LEF1 and SOX11 have excellent utility as diagnostic markers especially for atypical CD5-positive SBCLs.