Simple SummaryPatients with multiple myeloma (MM) who become refractory to three or more lines of therapy (RRMM patients) have few valid therapeutic alternatives. Among them, drugs directed against the BCMA antigen expressed in plasma cells are very appealing. Belantamab-mafodotin (belamaf) is the first antibody-drug conjugate against BCMA ready for clinical use. In this paper, we report the Spanish experience of belamaf monotherapy in 156 patients with RRMM. The overall response rate was 41.8%, with 39.8% of patients achieving a partial response or better. Median progression-free survival was 3.61 months, but interestingly, it increased to 14.47 months in patients achieving a minimal response or better. Treatment was well tolerated, ocular events being the most reported toxicity (87.9%; grade ≥ 3, 33.7%), but only two patients discontinued treatment due to side effects. Overall, our results confirm the safety and efficacy of belamaf in this poor prognosis subset of patients.AbstractBelantamab-mafodotin (belamaf) is a novel antibody-drug conjugate targeting B-cell maturation antigen that showed anti-myeloma activity in patients with relapsed and refractory multiple myeloma (RRMM). We performed an observational, retrospective, and multicenter study aimed to assess the efficacy and safety of single-agent belamaf in 156 Spanish patients with RRMM. The median number of prior therapy lines was 5 (range, 1–10), and 88% of patients were triple-class refractory. Median follow-up was 10.9 months (range, 1–28.6). The overall response rate was 41.8% (≥CR 13.5%, VGPR 9%, PR 17.3%, MR 2%). The median progression-free survival was 3.61 months (95% CI, 2.1–5.1) and 14.47 months (95% CI, 7.91–21.04) in patients achieving at least MR (p< 0.001). Median overall survival in the entire cohort and in patients with MR or better was 11.05 months (95% CI, 8.7–13.3) and 23.35 (NA-NA) months, respectively (p< 0.001). Corneal events (87.9%; grade ≥ 3, 33.7%) were the most commonly adverse events, while thrombocytopenia and infections occurred in 15.4% and 15% of patients, respectively. Two (1.3%) patients discontinued treatment permanently due to ocular toxicity. Belamaf showed a noticeably anti-myeloma activity in this real-life series of patients, particularly among those achieving MR or better. The safety profile was manageable and consistent with prior studies.