Model for risk adjustment of postoperative mortality in patients with colorectal cancer

A model was developed for risk adjustment of postoperative mortality in patients with colorectal cancer in order to make fair comparisons between healthcare providers. Previous models were derived in relatively small studies with the use of suboptimal modelling techniques.

Data from adults included in a national study of major surgery for colorectal cancer were used to develop and validate a logistic regression model for 90-day mortality. The main risk factors were identified from a review of the literature. The association with age was modelled as a curved continuous relationship. Bootstrap resampling was used to select interactions between risk factors.

A model based on data from 62 314 adults was developed that was well calibrated (absolute differences between observed and predicted mortality always smaller than 0·75 per cent in deciles of predicted risk). It discriminated well between low- and high-risk patients (C-index 0·800, 95 per cent c.i. 0·793 to 0·807). An interaction between age and metastatic disease was included as metastatic disease was found to increase postoperative risk in young patients aged 50 years (odds ratio 3·53, 95 per cent c.i. 2·66 to 4·67) far more than in elderly patients aged 80 years (odds ratio 1·48, 1·32 to 1·66).

Use of this model, estimated in the largest number of patients with colorectal cancer to date, is recommended when comparing postoperative mortality of major colorectal cancer surgery between hospitals, clinical teams or individual surgeons.