[A Case of Rheumatoid Arthritis Caused by Pembrolizumab Treatment for Non-Small Cell Lung Cancer].

A man in his 40s underwent a transbronchial lung biopsy and received a diagnosis of adenocarcinoma of the right upper lobe of the lung(cT4N0M0, Stage Ⅲ)with no EGFR gene mutation, no ALK fusion gene, no ROS1 fusion gene, and a tumor proportion score(TPS)of 50-74%. During the postoperative follow-up period, enlarged right supraclavicular lymph nodes and right upper and lower paratracheal lymph nodes were detected, diagnosed as recurrence by positron emission tomography-computed tomography. Although a positive rheumatoid factor test, as the patient had no symptoms of rheumatoid arthritis(RA), treatment with pembrolizumab was initiated. Before the second treatment course, a pharmacist conversing with the patient observed that the patient was experiencing pain in his fingers. After discussing the possibility of treatment continuation and test items with the attending physician, the patient underwent tests and received a diagnosis of RA.