What happened, in summary

This 59-year-old man had Stage IIB lung adenocarcinoma. He had a 30 pack-year smoking history and had quit 2 years before diagnosis. He had no history of psoriasis, autoimmune disease, chronic inflammatory disease, drug allergy, recent vaccination, or regular medication use before cancer treatment. In May 2021, he underwent right upper lobectomy by video-assisted thoracoscopic surgery. After surgery, he received adjuvant pembrolizumab 200 mg intravenously every 3 weeks. Thirteen days after the fourth pembrolizumab infusion, corresponding to day 78 after starting anti-PD-1 therapy, he developed itchy, scaly, red plaques on the limbs and trunk, mainly on extensor surfaces. About 10% of body surface area was involved. He did not have fever, joint pain, muscle pain, oral ulcers, or eye symptoms, and routine blood, liver, and kidney tests were normal. The event was graded as CTCAE grade 2. Skin biopsy showed psoriasiform changes with mixed inflammation, supporting pembrolizumab-associated psoriasiform dermatitis. The eruption was considered drug-dependent. Pembrolizumab was discontinued, and the cutaneous reaction resolved completely without long-term recurrence. The case also warns that switching to a different anti-PD-1 drug can trigger rapid recurrence of a similar rash; nivolumab was discussed in that context rather than as the original adjuvant treatment. During 3 years of follow-up after stopping immune checkpoint therapy, his lung adenocarcinoma remained stable with no radiologic or serologic evidence of recurrence. The story carries two outcomes: he avoided cancer recurrence, and the immune-related skin toxicity resolved after the checkpoint inhibitor was stopped. No PD-L1 result was stated.