Development of Monoclonal B-cell Lymphocytosis Shortly After Treatment with Nivolumab and Subsequent Progression to Chronic Lymphocytic Leukemia

Introduction Immune checkpoint inhibitors, such as programmed death (PD)-1 inhibitor nivolumab, are currently widely used in treatment of various malignancies. Due to their widespread application, any new potential adverse effects due to these agents necessitate careful assessment. Case report: We report a case of an 81-year-old man with recurrent high-risk malignant melanoma who underwent a 12-month adjuvant treatment with nivolumab. Shortly after the course of nivolumab, he developed monoclonal B-cell lymphocytosis (MBL) which subsequently progressed to chronic lymphocytic leukemia (CLL). Management and outcome: The patient is currently doing clinically well in Rai stage 0. Malignant melanoma remains in remission. Conclusion: Considering the pathophysiologic plausibility of nivolumab inducing B-cell dysregulation via PD-1 inhibition, we suggest further studies on potential association between nivolumab and B-cell malignancies.