DP053 | CD200, CD43 AND ROR1 INTEGRATION IN ROUTINE MULTIPARAMETRIC FLOW CYTOMETRY PANELS IMPROVE DIFFERENTIAL DIAGNOSIS ACCURACY OF B-CELL LYMPHOPROLIFERATIVE DISORDERS

Background: Clonal B-cell lymphoproliferative disorders (B-LPDs) are a heterogeneous group of neoplasms, whose accurate differential diagnosis can often be challenging. Multiparametric flow cytometry (MFC) is an essential analytical tool that provides critical insights for the B-LPDs diagnostic process. Methods: This study evaluates the role of MFC in B-LPDs differential diagnosis by analyzing expression and mean fluorescence intensity (MFI) of CD200, ROR1, and CD43 of these cells. Overall, 2688 MFC results of patients referred to our center for a B-LPD suspect were retrospectively analyzed. Results: In chronic lymphocytic leukemia (CLL), CD200, ROR1, and CD43 were constantly expressed with high intensity. The expression of CD200 in CLL samples [CD200%, mean: 100 (range, 23-100); positivity rate: 100%; MFI, mean= 170 (range, 11-1200)] was significantly higher than in mantle cell lymphoma (MCL) (p<0.001), usually negative for CD200, and in variant hairy cell leukemia (vHCL, 2022 ICC) (p<0.001), but similar to classical hairy cell leukemia (cHCL) (p>0.95). ROR1 was strongly expressed in both CLL [ROR1%, mean: 100 (range, 52-100), positivity rate: 100%; MFI, mean= 53 (range, 10-202)] and MCL with comparable MFI (p>0.95). The expression and MFI of CD43 were significantly higher in CLL [CD43%, mean: 99 (range, 60-100); positivity rate: 100%; MFI, mean = 216 (range, 44-984)] compared to MCL, vHCL, cHCL, and all other mature B-cell neoplasms (p <0.001). CD200 expression and MFI were significantly higher in cHCL [CD200%, mean: 100 (range, 100-100); positivity rate: 100%; MFI, mean= 120 (range, 20-1000)] compared to vHCL (p<0.001), as well as CD43 that showed higher mean expression in cHCL [43% (range, 0-100) vs 8% (range, 0-100)] (p=0.022), positivity rate (43% vs 6%) (p=0.030), and mean MFI [15 (range, 4-101) vs 8 (range, 3-74)] (p=0.034). Among other mature B-cell neoplasms, CD200 was variably expressed in follicular lymphoma (FL), marginal zone lymphoma (MZL), diffuse large B-cell lymphoma (DLBCL), and lymphoplasmacytic lymphoma (LPL). ROR1 and CD43 were mostly negative in this latter group. Persistent polyclonal B-cell lymphocytosis (PPBL) was uniformly positive for CD200 and negative for ROR1 and CD43. Conclusions: the evaluation of CD200, ROR1, and CD43, along with other commonly used MFC antigens, provides extremely useful insight for the timely and accurate differential diagnosis of B-LPDs and is currently indispensable for an optimal diagnostic workup.