ObjectiveAdequate knowledge of immune checkpoint inhibitors (ICIs) and associated immune-related adverse events (irAEs) is essential for managing such events. However, the level of knowledge among Japanese nurses remains unclear. This study aimed to investigate the current status of ICIs and irAE knowledge and the factors influencing them, among outpatient nurses caring for patients undergoing ICI treatment. MethodsAn exploratory cross-sectional study was conducted at 450 facilities nationwide. Participants completed a self-administered online questionnaire consisting of three parts, measuring personal and environmental attributes and awareness and knowledge of irAEs. Questions were based on multiple literature sources and were evaluated and validated by medical oncologists and certified oncology nurses. ResultsA total of 196 (response rate: 36.4%) nurses responded to the survey at 109 facilities (valid responses: 192; rate: 35.7%). The correct response rate was 27.6% for questions on general ICI knowledge and 15.6% for general irAE knowledge. Questions on pulmonary dysfunction had the highest correct response rate (41.7%), while those on neuromuscular/joint dysfunction had the lowest (1%). The mean correct response rates were 76% for general knowledge and 48.1% for ICI-specific knowledge. Multiple regression analysis showed that the most influential factor was the participants’ study schedule (P < 0.05). ConclusionsThere is room for nurses to acquire additional knowledge about ICIs and irAEs. The use of patient education tools and a study schedule significantly increased knowledge scores. Further research is needed to identify when and how to provide nurses with opportunities to acquire additional ICI and irAE-related knowledge.