IARS1 and metastatic neoplasm: Within the included RMS studies, data on IRS postsurgical stage were available for 80.35% (n = 33,382) of the patients, of whom 73.31% (n = 30,458) were categorised as having IRS I–III, while 7.04% (n = 2924) were classified as IRS IV (metastatic disease).