Severe oral erosive lichenoid reaction to pembrolizumab therapy.

New advances in cancer immunotherapy have been flooding the market at a rapid rate. Pembrolizumab (Keytruda), a programmed cell death protein 1 inhibitor, introduced in 2014, has been used to treat several cancers. Immune-related adverse events associated with pembrolizumab and other immune checkpoint inhibitors are now well-described complications. We describe the case of a 65-year old female with severe oral lichenoid lesions occurring after treatment with pembrolizumab for bladder cancer. To the best of our knowledge, this is the first report of a biopsy-proven oral erosive lichenoid reaction confirmed through direct immunofluorescence.