A single dose of pembrolizumab treatment causing a profound and durable response in lung cancer

Profound and durable responses to a single dose of pembrolizumab in lung cancer are rare. We encountered a non‐small cell lung cancer patient showing a deep and durable response with a single dose of pembrolizumab. A 79‐year‐old man reported bloody sputum for several weeks and visited a general physician. A chest x‐ray revealed a tumor shadow in the right middle lung field at that time, and the patient was referred to our hospital. He was diagnosed with adenocarcinoma of the lung by transbronchial biopsy. The expression of programmed death ligand 1 in tumor cells was 100% by immunostaining. Based on the above, immunotherapy with pembrolizumab was performed as first‐line therapy. Cancer cells had significantly shrunk at the end of the first cycle. The patient had grade‐3 immune‐related hepatitis at the end of the first cycle. Pembrolizumab treatment was stopped and prednisolone (80 mg/body) was initiated. Subsequently, liver function normalized, and prednisolone was tapered and discontinued. Since then, no tumor recurrence has been detected for 1.5 years without treatment. There have been few reports of profound and durable responses to a single dose of pembrolizumab in lung cancer. The results indicate that a single dose of pembrolizumab alone may be sufficient to cause durable response and serious immune‐related adverse events in some cases.