CD34-positive circulating cells quantification during follow-up in myeloproliferative neoplasms.

Polycythemia vera (PV) and Essential thrombcythemia (ET) are myeloproliferative neoplasms (MPNs) that can progress to secondary myelofibrosis, a complication associated with increased mortality. Circulating CD34-positive cells at diagnosis can be used to distinguish primary myelofibrosis from other MPNs with a threshold of 10/µL. In this study, we evaluate the interest of serial CD34-positive cell quantifications during the follow-up of MPNs. We retrospectively include 180 patients with MPN (90 ET, 55 PV and 35 myelofibrosis) with at least two measurements of circulating CD34-positive cells. CD34-positive cell count showed an AUC of 0.901 for the diagnosis of post-ET/PV myelofibrosis, with a sensitivity of 54.8%, a specificity of 99.5%, a PPV of 89.5% and a NPV of 96.3% for the threshold of 15 cells/µL. The decreased sensibility could be explained by an impact of cytoreductive treatments. Then we focused on primary and secondary myelofibrosis (MF) and found that patients achieving partial or complete response (per IWG-MRT criteria) had lower CD34-positive cell levels. Finally, CD34-positive cell levels had a prognostic impact on overall survival in MF, a count ≥ 100/µL is predictive of a higher risk of death (HR = 2.9 [1.5-5.9]), independently of DIPSS classification. In conclusion, monitoring of circulating CD34-positive cells is valuable for evaluating both disease progression and prognosis in MPN patients.