We retrospectively reviewed the medical records of patients diagnosed with MM according to the International Myeloma Working Group (IMWG) guidelines [15 (link)] at 10 medical centers in South Korea between December 2004 and June 2021. The inclusion criteria were as follows: (1) patients treated with daratumumab after more than three lines of therapy administered previously, including PI, IMiD, and/or ASCT, and (2) patients who received at least two cycles of daratumumab (total eight infusions) and underwent complete blood count (CBC) evaluation before and after daratumumab infusion. The exclusion criteria were as follows: (1) patients who received concurrent administration of other antimyeloma therapy with daratumumab and (2) patients with missing CBC values or whose treatment response was not assessed. This study was approved by the Institutional Review Board of Kyungpook National University Hospital (IRB no. 2021-05-13) and by each participating center in accordance with the Declaration of Helsinki. Written informed consent by the patients was waived due to a retrospective nature of our study.