CD200 is a useful marker in the diagnosis of chronic lymphocytic leukemia

BACKGROUND: The diagnosis of CLL is supported by a typical morphology and immunophenotype and usually does not present difficulties. Nevertheless, some patients with CLL can show an atypical phenotype, this raising the possibility of a lymphoproliferative disorder other than CLL. It has been recently shown that the expression of CD200 could be a rather consistent marker for CLL. METHODS: The expression of CD200 was investigated in 120 consecutive patients with B-cell chronic lymphoproliferative disorders (B-CLPD) (65 cases diagnosed as typical CLL, 16 atypical CLL, and 39 non-CLL before entering the study) by using multiparametric flow cytometry with four color combinations. CD200 was analyzed as percentage of positive cells (≥30%) and MFIR expression. ROC curves were used to determine the cut-off for the CD200 MFIR. Matutes score (MS) was used as comparator. RESULTS: All 81 (100%) patients classified as CLL and 25 of 39 (64.1%) classified as non-CLL expressed high CD200 expression (≥30%). CD200 expression showed a high sensitivity (100%) and a low specificity (35.9%), and the accuracy was similar to that of Matutes score markers (range: 79.2%-86.7%); except SmIg that was 59.1%. The addition of CD200 to the Matutes score correctly identified 74 of 81 (91.4%) CLL cases including 9 of 16 atypical CLL cases. As per non CLL cases, 37 of 39 (94.9%) were correctly diagnosed by the modified system. Altogether, CD200 improved the diagnostic accuracy of Matutes score from 86.7% to 92.5% (P < .01). CONCLUSION: These results show that CD200 is a valuable, albeit not specific, CLL diagnostic marker. © 2018 International Clinical Cytometry Society.