Seronegative rheumatoid arthritis after combination therapy with ipilimumab and nivolumab for postoperative pancreatic and liver metastases from renal cell carcinoma

INTRODUCTION: Since the approval of immune checkpoint inhibitors for renal cell carcinoma treatment, therapeutic efficacy has been enhanced. However, although autoimmune‐related side effects may occur, rheumatoid immune‐related adverse events seldom develop. CASE PRESENTATION: A 78‐year‐old Japanese man with renal cell carcinoma developed pancreatic and liver metastases after bilateral partial nephrectomy and was treated with ipilimumab and nivolumab. After 22 months, he developed arthralgia in limbs and knee joints, accompanied by limb swelling. The diagnosis was seronegative rheumatoid arthritis. Nivolumab was discontinued, and prednisolone was initiated, quickly improving symptoms. Although nivolumab was resumed after 2 months, arthritis did not recur. CONCLUSION: Immune checkpoint inhibitors may cause a wide variety of immune‐related adverse events. When arthritis is encountered during immune checkpoint inhibitor administration, seronegative rheumatoid arthritis should be differentiated from other types of arthritis, despite being less frequent.