Anti-PD-1/PD-L1 monoclonal antibodies result in a unique spectrum of side 
effects, widely known as immune-related adverse events. Toripalimab is 
an anti-PD-1 monoclonal antibody used for the treatment of some cancers. Here we 
report the first case, to our knowledge, of oral lichenoid drug reaction 
triggered by toripalimab. A 78-year-old man who was diagnosed with systemic 
metastatic prostate cancer presented with ulcers on the lower lip after the 
fifth cycle of toripalimab. We diagnosed him with oral lichenoid drug reaction 
based on clinical manifestation, histopathological findings and the history of 
anti-PD-1 therapy. The patient responded well to oral corticosteroids combined 
with helium-neon laser therapy. The anti-PD-1 therapy was not restarted because 
of stable disease, and the eruptions did not recur.