Non‐parallel anti‐tumour effects of pembrolizumab: a case of cardial tamponade

We present the case of a 70‐year‐old man with stage IV lung adenocarcinoma. He was treated with pembrolizumab, a programmed cell death‐1 (PD‐1) inhibitor, as a first‐line therapy. After six cycles of pembrolizumab, he suddenly developed cardiac tamponade. With the exception of newly massive malignant pericardial effusion, the other malignant lesions improved. Pembrolizumab was continued and the patient has shown a durable response for two years. This is the unique case of late‐onset pericaridial effusion with pembrolizumab, showed discrepant anti‐tumour effects. A proper assessment is crucial to ensure favourable clinical outcomes in patients treated with PD‐1 inhibitor.