A retrospective analysis of clinical features and treatment outcome in 21 patients with immunoglobulin M-related light-chain amyloidosis in Japan: a study from the Amyloidosis Research Committee.

We retrospectively gathered data of 21 patients (13 male and 8 female; median age 65 years) diagnosed with immunoglobulin M (IgM)-related light-chain (AL) amyloidosis in Japan to investigate characteristics of IgM-AL amyloidosis and its optimal treatment strategy. Median IgM and difference free light chain (FLC) at diagnosis were 1257 mg/dl and 34.3 mg/l, respectively. Organ involvement was observed in the heart in 7 patients (33%), kidneys in 15 (71%), and lymph nodes in 5 (24%). Initial treatments were melphalan/dexamethasone in 7 patients, bortezomib/cyclophosphamide/dexamethasone in 3, autologous stem cell transplantation in 3, rituximab/bendamustine in 1, other in 3, and none in 4. Hematological responses among 15 evaluable patients were as follows: 3 reached complete response (CR), 4 partial response (PR), and 1 very good PR (VGPR), making the overall response rate of PR or better 40%. Median overall survival (OS) was 14.0 months and 1-year OS was 71.4%. Prognosis was significantly poorer in patients with cardiac involvement than those with non-cardiac involvement (1-year OS 27.8% vs. 85.7%, p = 0.0468). The involved FLC value was low in several patients and therapeutic response was difficult to assess. Further study is necessary to determine the optimal treatment for IgM-AL amyloidosis.