Carfilzomib‐induced hemolysis is noticeably common but rarely shows features of thrombotic microangiopathy: A retrospective study

OBJECTIVE: Hemolysis is a sporadically reported but potentially serious side effect of the proteasome inhibitor carfilzomib. We aimed to investigate the frequency of hemolysis in an unselected cohort. METHODS: We performed a retrospective, single‐center study of the incidence of hemolysis in patients treated with carfilzomib, based mainly on consecutive haptoglobin levels. The patients were diagnosed with myeloma (n = 20), AL amyloidosis (n = 3), and light‐chain deposition disease (n = 1). Carfilzomib treatment was applied after a median of 3 (range: 1‐7) therapy lines. RESULTS: Haptoglobin levels were normal/increased before, generally suppressed during, and normalized after treatment with carfilzomib. Very low haptoglobin (<0.1 g/L) implying the presence of hemolysis was observed in 16 of 24 (67%) patients during carfilzomib therapy. Hemolysis was mild in 11 of 16 (69%) affected patients, whereas 5 of 16 (31%) required transfusion. Severe hemolysis was explained by thrombotic microangiopathy (TMA) in one patient who died of the complication. Mechanisms were unclear in the remaining 15 patients. CONCLUSIONS: Hemolysis was surprisingly common but mostly mild during carfilzomib treatment. However, the possibility of TMA should be kept in mind in this setting. Hypothetically, non‐TMA hemolysis could be attributed to the accumulation of globin chains due to the suppression of eukaryotic translation initiation inhibition by carfilzomib.