This article is aimed to report our initial experience with the bispecific T-cell engager teclistamab administered with concomitant radiotherapy, including reirradiation, in two patients with widespread multiple myeloma, including hepatic and meningeal relapse, respectively. This is a retrospective patient record assessment at a single institution. Both patients had previously received several lines of systemic therapy and radiotherapy to multiple target volumes, resulting in a considerable cumulative bone marrow dose when completing their recent courses in 2025. The Patient 1 started current radiotherapy with already compromised blood cell counts, while the Patient 2 had preserved values, except for lymphocytes. Both patients rapidly developed grade 4 haematological toxicity (white blood cells and platelets) but recovered within few weeks. Radiotherapy did not cause other acute toxicity greater than grade 2. Given the serious haematological toxicity observed in our patients, hospitalization and close monitoring by a dedicated team of experienced haematologists may become necessary in complex settings like those described here. Their expertise might also be required to manage cytokine release syndrome and potentially life-threatening neutropenic infections.