IgM AL amyloidosis: delineating disease biology and outcomes with clinical, genomic and bone marrow morphological features.

This study evaluates newly diagnosed IgM (6%, n = 75/1174) vs. non-IgM light chain amyloidosis patients. IgM amyloid patients had lower light chains (12.5 vs. 22.5 mg/dL; p < 0.001). Heart (56% vs. 73%, p = 0.002) and >1 organ involvement (31% vs. 44%, p = 0.02) was less common in IgM amyloidosis, while soft tissue and peripheral nerve involvement was more common. t(11;14) was less common (27% vs. 50%, p = 0.008) in IgM amyloidosis. Rates of MYD88L265P and CXCR4WHIM mutation in IgM amyloidosis were 58% (29/50) and 17% (8/46). Diagnosis after hematopathology review in IgM amyloidosis was pure plasma cell neoplasm (PPCN) in 23% (16/70), lymphoplasmacytic neoplasm (LPL) in 63% (44/70) patients, and other (14%). LPL vs. PPCN groups had distinct genetic abnormalities: t(11;14): 0% (0/18) vs. 60% (9/15), p < 0.001; MYD88L265P mutation: 84% (27/32) vs. 0% (0/14), p < 0.001; CXCR4 mutation: 29% (8/28) vs. 0% (0/14), p = 0.04. Overall survival was shorter in IgM AL when stratified by Mayo 2012 stage; stage 1/2 (59 vs. 125.9 months, p = 0.003) and stage 3/4 (6.5 vs. 12.9 months, p = 0.075), likely due to lower hematologic response rates (6 months: 39% vs. 59%, p = 0.008). We characterized two subtypes of IgM amyloidosis (LPL/PPCN). This can aid in therapeutic decision-making, with treatment directed at the clonal disease.