Immunophenotype Drift of Residual Plasma Cells Indicates Therapeutic Response and Prognosis in Multiple Myeloma

Background Chemotherapy resistance remains a significant hurdle in the treatment of multiple myeloma (MM). However, it is difficult to discriminate the potential refractory patients from the very early stage. Flow cytometry is a convenient tool to detect the residual myeloma cell tiding, indicating therapeutic response sensitively. Methods From June, 2014 to December, 2016, 172 sequential patients with newly diagnosed multiple myeloma were enrolled in the BDH2008/02 clinical trial. Patient informed consent was obtained in accordance with the Declaration of Helsinki. 144 patients with at least two flow cytometry detections were analyzed. Bone marrow samples were detected by an eight-color EuroFlow panel. CD20 negative and CD81 positive is defined as normal phenotype. Results We conducted a median of 3-time (2-8) flow cytometry detection on each patient. When newly diagnosed and achieved best response, CD20, CD81 expression rates were 29.9%, 9.7% and 14.9%, 64.4% (P=0.0091, P<0.0001), respectively. According to the status variation of CD20 and CD81, all patients were divided into three groups: both markers were always normal (Group A), either CD20 or CD81 was abnormal at diagnosed and turned normal during therapy (Group B) and markers stayed abnormal (Group C). Patients with undetectable residual tumor cells were also classified as Group A. The overall response rate of the patients in Group C was inferior to Group B (>PR rate: 54.3% vs. 71.4%, P=0.021). And the OS of Group C was significantly worse than Group A and B (47.9 months vs. not reached vs. not reached, P=0.036). Conclusion CD20/CD81 switching to normal phenotype during therapy indicates therapeutic response and an improved outcome than that staying abnormal. The expression tiding of CD20 and CD81 may be a reasonable combination to dynamically stratify MM patients, directing the choice of maintenance therapy. Figure Disclosures No relevant conflicts of interest to declare.