This is a non-interventional, national, multicentre retrospective and prospective observational study aiming at assessing the efficacy of isatuximab-based regimens in RRMM patients with 1q21+ in a real-life setting. Due to the limited information as to isatuximab's impact in real-world settings and that MM is a rare cancer, patients will be enrolled both prospectively and retrospectively from approximately 8 haematologic/oncologic centers in Italy. Prospective enrollment will allow an assessment of true baseline and the beneficial treatment of isatuximab among RRMM patients with 1q21+. The inclusion of retrospectively enrolled patients previously exposed to isatuximab-based regimens (Isa-Pd and Isa-Kd) will allow for maximal data capture to evaluate isatuximab treatment as part of routine care. All the sites participating in the study are using isatuximab-based regimens for the treatment of RRMM patients in clinical practice. According to data availability and/or clinical experience of the sites, data from approximately 150 patients consecutively treated in the participating centers will be collected in the present study and compared with data published in the literature.