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Invited Critique
November 1, 2007

Comparison of P-POSSUM and Cr-POSSUM Scores in Patients Undergoing Colorectal Cancer Resection—Invited Critique

Arch Surg. 2007;142(11):1048. doi:10.1001/archsurg.142.11.1048

Assessment of outcomes for surgical services may become an important way for the government and insurance companies to grade health systems, hospitals, and individual practitioners. Any time outcomes are evaluated or compared, a method of assessing the influence of medical comorbidity on the selected outcome of a selected procedure for a selected disease must be provided to make the evaluation meaningful. POSSUM, P-POSSUM, and Cr-POSSUM scores are methods for assessing the severity of comorbid and operative factors that might influence surgical outcomes using complicated formulas associating numerous data points that include medical comorbidity and operative severity factors. Senagore and colleagues1 showed that the 3 POSSUM scores need to be calibrated by each system and suggest that comparison between 2 systems should be undertaken carefully. The Cr-POSSUM score predicts mortality closely even though missing data from the medical records of patients causes little variation in the ability to predict outcome for colon cancer. This suggests that the score for an individual patient may not be reliable. Therefore, we must be careful when using the scores to predict individual patient outcomes, influence selection of a complicated procedure, and determine futility of operative management of advanced disease on the basis of individual POSSUM scores. In the article by Horzic et al this point is emphasized by calculating the AUC. The value of 0.59 for Cr-POSSUM indicates almost random prediction of mortality for an individual patient, even though it is an accurate predictor for a population of patients with colorectal cancer. It is unlikely that the Cr-POSSUM score will ever be calculated for use in an individual patient as part of the decision making preoperative process.