Aberrant expression of CD56 on granulocytes and monocytes in myeloproliferative neoplasm

We reviewed CD56 expression on bone marrow (BM) granulocytes and monocytes by flow cytometry in 101 cases of myeloproliferative neoplasm (MPN) and compared them with those from 42 cases of myelodysplastic syndrome (MDS), 47 cases of negative BM after stem cell transplantation, and 24 cases of negative BM after chemotherapy. Forty cases of negative staging BM for lymphoma were used as negative controls. CD56 expression on granulocytes was also compared with corresponding morphologic and molecular genetic findings in five patients who underwent serial BM sampling. Using 10 % as positive threshold, aberrant CD56 expression was detected on granulocytes and monocytes in 20 and 34 % cases, respectively, in MPN, and in 18 and 36 % cases, respectively, in high-grade MDS. Aberrant CD56 expression was present in all subtypes of MPN with the highest frequency seen in primary myelofibrosis (37 % on granulocytes, 40 % on monocytes). Compared to monocytes, granulocytes had lower frequencies of CD56 expression but higher specificity for abnormal cells. Low levels of CD56 expression were detected on the granulocytes in normal BM after chemotherapy and stem cell transplantation, but the expression levels were generally below 10 %. In the patients with serial samples, CD56 expression paralleled with disease status by BM morphology, BCR/ABL1 transcripts, or percentage of BM recipient cells. We conclude that aberrant CD56 expression on granulocytes is present in a subset of patients in all subtypes of MPN. Identification of abnormal CD56-positive granulocytes is helpful in both initial diagnosis and follow-up of patients in MPN.