Raimbault A, et al. - Whether the expression of the myeloid marker CD13 (also termed ANPEP), which has been suggested to be more frequent in lymphoplasmacytic lymphoma (LPL) than in other B-cell lymphoproliferative disorders (B-LPD), could discriminate Waldenström Macroglobulinaemia (WM)/LPL from other B-LPD was investigated in a cohort of 1037 B-LPD patients from 3 centres. Flow cytometry was used to assess CD13 expression. Researchers found a variable percentage of CD13-expressing cells among B-LPD but these cells were remarkably higher in WM/LPL (median 31% vs 0% in non-WM/LPL). CD13 expression was significantly related to a diagnosis of WM/LPL. The best diagnostic performance for WM/LPL assertion was seen at a cut-off value of 2% of CD19+ cells co-expressing CD13. The hypothesis of some post-transcriptional regulation must be favoured as no difference in CD13 (also termed ANPEP) mRNA between normal and pathological B-cells was reported in previously published transcriptomic data. Overall, CD13 expression testing by flow cytometry offered aid to discriminate WM/LPL from other B-LPD.