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 IV haematological

toxicity (white blood cells and platelets) but recovered within few

weeks. Radiotherapy did not cause other acute toxicity greater than

grade II. 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.