PDCD1 and type 1 diabetes mellitus: This report presents a rare case of DKA and IDDM secondary to anti-PD-1 antibody cemiplimab therapy, and this is the third described in the literature to date.<h4>Case presentation</h4>We describe the case of a 62-year-old female patient with metastatic perianal squamous cell carcinoma who developed DKA and IDDM after the fifth cycle of cemiplimab.