Case Mix Difference Can Affect Evaluation of Outcome of Treatment for Colorectal Cancer

To explore the potential effects of patient selection, for example by organization, on survival as outcome parameter in colorectal cancer treatment.

The main cohort was identified in a Hospital-based registry and outcome data of all 2,717 patients operated on for colorectal cancer between 2000-2011 were evaluated. A simulation of different center settings was performed using several potential selection criteria, including emergency cases, referral surgery and palliative resection, and used for comparison of outcome data.

Overall survival and cancer-specific survival can be significantly affected in both short-term (30-/90-day) mortality and long-term survival by factors of organizational level.

Survival data as an outcome parameter can be affected by the composition of the patient cohort and thus reflect possible selection bias for example due to organization, referral patterns and practice customs. This potential bias should be acknowledged when making inter-hospital comparisons of outcome.