We present the case of a 53-year-old woman treated with analgesic radiotherapy for a multiple myeloma bone lesion of the forearm. After a first fraction of 5 Gray (Gy), she presented with an acute respiratory syndrome with fever a few hours after the treatment. The same symptoms occurred after the second fraction 3 days later. The patient recovered quickly thanks to intravenous hydration and suspension of the radiotherapy. Biological tests revealed a tumor lysis syndrome. We concluded that the clinical symptoms could be defined as cytokine release syndrome. This is the second time in the literature that cytokine release syndrome has been described following radiotherapy. First, we synthesize TLS and radiotherapy to determine how radiotherapy could be a trigger associated with other well-known factors. Furthermore, we discuss radiotherapy and cytokine release syndrome. Summary: We present the case of a woman treated with analgesic radiotherapy for a multiple myeloma bone lesion. Following the first and the second treatment fraction, the patient presented with an acute respiratory syndrome with fever and biological tests revealed a tumor lysis syndrome. We concluded that the clinical symptoms could be defined as cytokine release syndrome. Furthermore, we discuss how radiotherapy could be a trigger of cytokine release syndrome and tumor lysis syndrome in association with chemotherapy drugs.