Hematologic response assessment in monoclonal gammopathy of renal significance: critical appraisal of current criteria.

INTRODUCTION: Current recommendations for hematologic response (HemR) assessment in monoclonal gammopathies of renal significance (MGRS) are based on the monoclonal immunoglobulin (MIg) component responsible for renal damage. Light-chain (LC) amyloidosis criteria are recommended when renal lesions are due to LC, whereas multiple myeloma (MM) criteria are proposed when due to an intact monoclonal immunoglobulin. However, the nephrotoxic MIg is frequently not measurable either by the International Myeloma Working Group (IMWG) or the International Society of Amyloidosis (ISA) criteria. METHODS: In the study shown below, we retrospectively analyzed an original multi-center series of 45 MGRS patients. RESULTS: Thirty-two MGRS-non-amyloidosis (MGRS-NA) and 13 MGRS-amyloidosis (MGRS-A) patients were included. Twelve (37.5%) and 15 (47%) MGRS-NA patients had measurable disease by either the IMWG or ISA criteria, respectively. According to the IMWG criteria, 5% of MGRS-NA patients with intact MIg renal deposits and 80% with exclusively LC deposits had measurable disease, as determined by serum electrophoresis or sFLC assay, respectively. Based on the ISA criteria, 35 and 80% of MGRS-NA patients with MIg and LC renal deposits, respectively, had measurable disease. DISCUSSION: Our findings reveal the limitations of the current proposed HemR assessment in MGRS-NA patients and explore potential alternatives to ease clinical practice and guideline development.