Inadequate prediction of postoperative complications in breast cancer surgery: An evaluation of the ACS Surgical Risk Calculator

Background The American College of Surgeon (ACS) Surgical Risk Calculator is an online tool that helps surgeons estimate the risk of postoperative complications for numerous surgical procedures across several surgical specialties. Methods We evaluated the predictive performance of the calculator in 385 cancer patients undergoing breast surgery. Calculator‐predicted complication rates were compared with observed complication rates; calculator performance was evaluated using calibration and discrimination analyses. Results The mean calculator‐predicted rates for any complication (4.1%) and serious complication (3.2%) were significantly lower than the observed rates (11.2% and 5.2%, respectively). The area under the curve was 0.617 for any complication and 0.682 for serious complications. p Values for the Hosmer–Lemeshow test were significant (