LEF1: a highly specific marker for the diagnosis of chronic lymphocytic B cell leukaemia/small lymphocytic B cell lymphoma

Abstract

AIMS: Chronic lymphocytic B cell leukaemia (CLL)/small lymphocytic B cell lymphoma (SLL) has proven to be not a uniform entity but to consist of various disease subtypes. CLL might also pose diagnostic challenges by demonstrating an uncommon immunohistochemical profile. Recently, the role of lymphocyte enhancer-binding factor 1 (LEF1) in CLL was elucidated being highly expressed and seeming to have a prognostic value. Our aim was to test the applicability of LEF1 as marker for CLL in a diagnostic setting. METHODS: We investigated LEF1 expression in lymphomas by immunohistochemistry on tissue microarrays containing several lymphoma entities (altogether 720 cases, including 61 CLL cases). We also separated CLL cases by zeta-chain-associated protein kinase 70 (ZAP70) and CD38 stainings and fluorescence in situ hybridisation analyses for TP53 deletions and trisomy 12 into respective groups and correlated data with LEF1 expression. RESULTS: The area under the receiver operating characteristic curve for LEF1 as a diagnostic marker for CLL was 0.815 (95% CI 0.742 to 0.888). The relevant diagnostic cut-off value for LEF1 positivity determined by the Youden's index was 10% (specificity 92%, sensitivity 70%). The majority of CLL cases (70%) expressed LEF1. Eighteen per cent of (transformed) diffuse large B cell lymphoma cases also expressed LEF1. In most other lymphoma entities, LEF1 was negative. There was a positive correlation of LEF1 staining with ZAP70 expression (Spearman's rho: 0.438, p<0.001), but not with CD38 expression, TP53 deletions or trisomy 12. CONCLUSIONS: LEF1 is a useful marker in the differential diagnosis of CLL in difficult cases. It shows a high specificity (92%) and a reasonable sensitivity (70%) for this entity.