B2M and neoplasm: Serum β2M is a marker of tumor load in lymphoproliferative disorders (including MM) and of kidney insufficiency, both important predictors of outcome in MM.31 Together with albumin, serum β2M is a key factor in current International Staging System,32 but it also predicts progression from smoldering‐MM to symptomatic disease, response to chemotherapy, relapse, and even prognosis after transplantation.33, 34, 35 This is the first study in which β2M was also found to be an independent prognostic factor of AKI following ASCT for MM.