Recurrence of generalized cutaneous lichen planus after switching from PD-1 to PD-L1 in a patient with pre-existing oral lichen planus: a case report.

We present a clinicopathologically documented case of generalized cutaneous lichen planus that recurred after switching from a programmed death 1 (PD-1) inhibitor (camrelizumab) to its ligand PD-L1 inhibitor (atezolizumab) in a patient with pre-existing oral lichen planus. While relapse of induce immune-related adverse events (irAEs) after PD-1/PD-L1 switching has been previously reported, most of these reports described cutaneous manifestations merely as "rash" without detailed dermatological characterization. In contrast, detailed clinical characterization-including clinical photographs, semi-quantitative histopathology, Naranjo causality assessment, treatment response, and long-term follow-up-for a precisely diagnosed cutaneous lichen planus recurrence remains rarely documented. The patient was a 58-years-old female with a 20-years history of oral lichen planus. Following a diagnosis of non-small cell lung cancer (NSCLC), she received camrelizumab. One month later, she developed a generalized cutaneous lichen planus flare, prompting discontinuation of camrelizumab and a switch to atezolizumab. After eight cycles of atezolizumab, the same lichen planus recurred at the identical body sites with greater severity. At admission, the pruritus Visual Analogue Scale (VAS) score was 8. A skin pathology biopsy supported the diagnosis of lichenoid interface dermatitis, with perivascular eosinophil infiltration in the mid-to-deep dermis, consistent with a drug-related etiology. After following treatment with prednisone at a maximum dose of 33 mg, the score decreased to 2. During 10 months of follow-up after discharge, the patient remained stable with no recurrence. This case suggests that recurrence of cutaneous irAEs may occur during sequential use of PD-1 and PD-L1 inhibitors in patients with a history of autoimmune disease.