Remitting seronegative symmetrical synovitis with pitting edema syndrome induced by pembrolizumab in patient with urothelial carcinoma

INTRODUCTION: Recent introduction of immuno‐oncology drugs such as pembrolizumab has resulted in improved outcomes for urothelial carcinoma patients. However, immune‐related adverse events generally show great variance and are often difficult to diagnose and control. CASE PRESENTATION: An 84‐year‐old Japanese male with urothelial carcinoma metastasis to the lungs after a laparoscopic left radical nephroureterectomy procedure was treated with pembrolizumab, an immuno‐oncology drug, as second‐line therapy. At week 6, inflammatory arthralgia involving the hands and shoulder joints, and edema of the hands were presented. The diagnosis was remitting seronegative symmetrical synovitis with pitting edema syndrome. Pembrolizumab was discontinued, and oral corticosteroid therapy was started. Two months later, pembrolizumab treatment was resumed because of a significant improvement in patient condition. CONCLUSION: Although rare, immune‐related adverse events are occasionally encountered during the use of immune‐oncology drugs; thus, early diagnosis and appropriate treatment are important.