Clinical Presentation and Long-Term Survival Outcomes of Patients With Monoclonal Gammopathy of Renal Significance (MGRS): A Multicenter Retrospective Study

Introduction: MGRS are new rare clinical entities, whose recognition and optimal management is evolving. Methods: To implement real-life data, we retrospectively analysed a multicentre cohort of 60 patients with renal biopsy-proven MGRS receiving mainly novel treatments (between 2006 and 2021) in eight Italian centres. Based on renal biopsy, patients were divided into two subgroups: AL amyloidosis (70%, n = 42) and other-MGRS (30%, n = 18). Results: Baseline characteristics follow typical manifestations of MGRS disorders in terms of small clonal burden, laboratory and clinical features. More patients with AL amyloidosis had monotypic lambda light-chain disease, estimated glomerular filtration rate (eGFR) ≥ 60 mL/min and nephrotic proteinuria than other-MGRS group. The most widely used drug was bortezomib, and about one-third of patients underwent ASCT. Overall response rate was 86% with no differences in the two subgroups. However, high-quality hematologic responses ≥very good partial response (VGPR) were greater in AL amyloidosis than in other-MGRS group (67% vs 28%, p = 0.015). The depth of haematological response influenced renal response, obtained in 32 (59%) of evaluable patients, similarly in the subgroups. Indeed, 75% patients with ≥ VGPR (p = 0.049) and none with stable disease (p ≤ 0.001) obtained a renal response. No association between renal response and histotypes (p = 0.9) or type of first-line therapy (p = 0.3) was found. At a median follow-up of 54.4 months (IQR 24.8–102.8), median progression-free survival (PFS) was 100.1 months (95% CI 34.9–NR), and median overall survival not reached (95% CI 129.8–NR). No significant difference emerged between the two groups in terms of survival outcomes. Achieving ≥ VGPR was confirmed as the main independent predictor of prolonged PFS in the general population (HR = 0.29, p = 0.023) and AL amyloidosis group (HR 0.23; p = 0.023). Preserved renal function at diagnosis was predictive of improved PFS in the AL amyloidosis group (eGFR ≥ 60 mL/min: HR = 0.003; p = 0.018; eGFR 30–60 mL/min: HR = 0.04, p = 0.046). Conclusion: Further research is warranted to develop standardised response criteria and treatment strategies to improve MGRS management.