CPC02 Delayed widespread lichenoid drug reaction with radioisotopic response in a patient treated with nivolumab

The introduction of immune checkpoint inhibitors for the treatment of a wide variety of malignancies has led to a rise in cutaneous immune-related adverse events (irAEs), including autoimmune and autoinflammatory skin conditions, which typically present within the first 16 weeks of treatment—on average, 3.6 weeks after drug initiation. Cutaneous irAEs occur in approximately 8.7% of patients receiving antiprogrammed cell death type 1 therapy (PD-1). Nivolumab is an antibody against PD-1 widely used for various cancers. As the application of these therapies expands, understanding of their adverse cutaneous effects is essential. We present a 76-year-old woman with metastatic renal cell carcinoma, who developed a widespread pruritic eruption 18 months after commencing nivolumab. Examination revealed a papular and vesicular rash affecting the arms, legs, anterior chest, face, hands and feet. There was a confluent well-demarcated rectangular area of grouped papules on the right side of her back; this site had been treated with radiotherapy for localized rib metastases 1 month prior to onset of rash. There was no mucosal involvement and no systemic symptoms. Three skin biopsies were taken, which showed vacuolar alteration of the basal layer and a band-like inflammatory cell infiltrate at the dermoepidermal junction, with focal areas of subepidermal separation. Direct immunofluorescence was negative, and skin swabs were negative for bacterial and viral infection. A diagnosis of delayed bullous lichenoid drug reaction secondary to nivolumab was made. The area involving the previous radiotherapy field was considered to be a radioisotopic response rather than a radiation recall response as she was already on nivolumab when it occurred. She discontinued nivolumab and commenced oral prednisolone and her skin settled over 5 weeks. Lichenoid dermatitis is a known adverse reaction associated with PD-1 therapy, with improved survival outcomes noted in patients with lichenoid irAEs on PD-1 therapy. Typically, it occurs within 16 weeks, with a documented range of 1–266 days. This patient developed a delayed lichenoid eruption at approximately 550 days, with concurrent radioisotopic response at a previous radiotherapy site. Radiotherapy-induced lichen planus is rare, with only one case report documenting involvement outside the irradiated field. We found no previous reports of nivolumab causing lichenoid drug eruption after such a protracted period. This case adds to the grow