Erythema multiforme associated with cancer radiotherapy: A single‐institution case series and literature review

Abstract Radiation dermatitis, limited to the irradiated site, is the most common cutaneous adverse reaction due to radiotherapy. There are scattered reports of erythema multiforme‐like rash, Stevens–Johnson syndrome, and toxic epidermal necrolysis associated with radiotherapy. Some of these reports include cases without remarkable drug history, which suggests rashes induced by radiotherapy. The lack of a large cohort study, however, makes it difficult to ascertain the time course, severity, and outcome of the cases. We aimed to evaluate the potential association between radiotherapy and erythema multiforme‐like rash in a larger sample of patients. We examined the records of patients at our institute who received radiotherapy and developed a rash from 2010 to 2021. We present 30 patients with erythema multiforme‐like rash, which arose during or after radiotherapy. We describe the background, details of radiotherapy, and clinical course of the patients including the cutaneous and extracutaneous symptoms. Radiotherapy was the most likely cause of rash, and in most cases, the rash was relieved by conservative management and radiation could be continued. When erythema multiforme‐like rash arises in patients under cancer treatment, radiotherapy should be considered a potential trigger.