Evaluation of CD56 and CD117 Double-Positivity as a Predictor of Poor Prognosis in Multiple Myeloma Patients: A Retrospective Analysis

Objective: Despite advancements in treatment, multiple myeloma (MM) remains a challenging hematologic malignancy. It is crucial to stratify risk and perform prognostic assessment with various markers, including the expression of cluster of differentiation 56 (CD56) and cluster of differentiation 117 (CD117). However, the relationship of these markers with MM-related survival remains unclear. In this context, the objective of this study was to investigate the prognostic implications of CD56 and CD117 expression and associated clinical features in MM patients. Materials and Methods: The population of this retrospective single-center study consisted of adult MM patients whose CD56 and CD117 expression levels were analyzed. Patients were divided into four groups according to their immunophenotypes: CD56(+)CD117(-), CD56(-)CD117(+), CD56(+)CD117(+), and CD56(-)CD117(-). These groups were compared in terms of demographic and clinical characteristics, response to treatment, and survival outcomes. Results: Of the 168 MM patients included in the study, CD56 positivity, CD117 positivity, CD56 and CD117 double positivity, and CD56 and CD117 double negativity were observed in 57.1%, 38.1%, 21.4%, and 26.2%, respectively. Patients with double positivity had significantly higher cytogenetic risk and significantly lower overall response rate (ORR) compared to other patients (p<0.001 for both). ORR and overall survival (OS) were significantly lower in CD56(-)positive patients than in CD56(-)negative patients (p=0.017 and p=0.004, respectively). Mortality rates were significantly higher in CD56(-)positive and CD117positive patients than in double-negative patients (p<0.001 and p=0.002, respectively). Double-negative patients had significantly lower ORR and OS and higher mortality than others (p=0.001, p=0.002, and p<0.001, respectively). High cytogenetic risk was found to be an independent predictor of shorter OS (p>0.001). Conclusion: This study's findings revealed that MM patients with CD56 and CD117 double positivity had poorer prognosis, lower ORR, shorter OS, and higher mortality.