Belantamab mafodotin (BLMF) is an interesting therapeutic alternative for multiple myeloma (MM) patients pretreated with immunomodulatory drugs, proteasome inhibitors, and anti-CD38 monoclonal antibodies. Scientific evidence on BLMF provides immature data about progression-free survival and overall survival by short follow-up of patients with poor prognoses. Cases with long follow-ups could provide additional information about BLMF. This case reports a patient with MM treated with BLMF who had received nine previous lines of therapy with a follow-up of 11 months. No complete response was obtained. However, no disease progression was observed and the patient was still alive at the end of this work. BLMF showed manageable adverse effects. Our patient presented advanced disease, good functional status at the beginning of BLMF treatment, and elevated levels of lactate dehydrogenase during BLMF therapy. The influence of these last two factors was not evaluated in clinical trials. This relationship should be assessed more deeply in future studies.