Use of High- and Medium-Cut-off Membrane Hemodialysis for Removal of Free Light Chains in Patients with Multiple Myeloma—A Single-Center Experience

Background/Objectives: Light-chain cast nephropathy remains a major cause of morbidity in newly diagnosed multiple myeloma (MM), and rapidly reducing circulating free light chains (FLCs) is considered essential for renal recovery and survival. Methods: We conducted a single-center retrospective study evaluating high- and medium-cut-off hemodialysis (HCO/MCO HD) in newly diagnosed MM patients presenting with acute kidney injury (AKI). Consecutive patients treated at the University Medical Center Ljubljana between 1 January 2020 and 31 December 2023 were included. As per institutional protocols, HCO/MCO HD- and myeloma-directed therapy were initiated on the day of diagnosis. Primary endpoints were the magnitude of FLC reduction, renal and hematologic responses at three months, and overall survival. Results: The median FLC concentration at presentation was 9630 mg/L. FLC levels declined rapidly after HCO/MCO HD initiation, reaching 2400 mg/L by day 7, 1083 mg/L by day 14, and 370 mg/L by day 30. MCO HD achieved kapa FLC clearance comparable to HCO HD for the lambda isotype. Despite a median of only four HCO/MCO-HD sessions, the reduction in FLC was rapid, with an additional decline observed over time, while the median FLC concentration fell below 500 mg/L. At three months, the overall hematologic response was 87%, including very good partial response or better in 35% of patients, and renal response in 79% of patients. Achieving a ≥70% FLC reduction by day 7 was associated with superior outcomes, including markedly longer median overall survival (82.5 vs. 23.2 months). Conclusions: Our data show that HCO/MCO-HD treatment alongside anti-myeloma therapy achieves sustained FLC reduction in newly diagnosed MM with AKI and early FLC reduction is highlighted as a key determinant of survival.