What happened, in summary

A 68-year-old man with advanced lung adenocarcinoma had a PD-L1 tumor proportion score of 95% and began pembrolizumab as first-line treatment. A partial response was seen 2 months after treatment started. He remained on pembrolizumab for 66 months. During that long treatment course, he also developed adrenal insufficiency related to pembrolizumab and required hydrocortisone. Later, an expanding skin rash progressed to erythema and tense blisters on the lower legs. Skin biopsy, immunofluorescence testing, and an elevated anti-BP180 antibody level supported a diagnosis of bullous pemphigoid. Pembrolizumab and a diabetes medication that could also contribute to the condition were discontinued. Prednisolone led to complete resolution of the skin symptoms within 3 months, although a low steroid dose was still being used at the latest follow-up. Twelve months after the bullous pemphigoid diagnosis, the lung cancer had not progressed despite pembrolizumab remaining discontinued. His course shows durable disease control after a prolonged immunotherapy response complicated by significant immune-related adverse effects.