Seasonal variation in short-term mortality after surgery for colorectal cancer?

Abstract Aim: Comorbidity has a major impact on short-term and long-term survival of colorectal cancer (CRC) and many CRC patients suffer from comorbidities. Mortality rates for comorbidities like cardio-respiratory diseases exhibit distinct seasonal variations with highest rates in the winter. Therefore, we hypothesized some seasonal variation in 30-day mortality after surgery for CRC as well. Methods: In a nationwide study, we examined the seasonal pattern in 30-day mortality after surgery for CRC from 1996 to 2006. We identified 33,556 CRC patients in the Danish hospital discharge registries. Monthly 30-day mortality rates were calculated and we constructed a fitted curve of the monthly mortality rates using a periodic regression model. We stratified the analyses for tumour site, urgency of surgery for colon cancer and the level of comorbidity based on American Society of Anaesthesiologists (ASA) score. Results: The overall 30-day mortality was 8.7% (95% CI: 8.4%-9.0%). Significant seasonal variation in monthly 30-day mortality could not be identified. For colon cancer, a non-significant increase was seen in July. An even higher increase in July was observed for CRC patients with moderate or severe comorbidity (ASA score >/=III), but was also non-significant. Conclusion: Although comorbidity is a well-known negative predictor of short-term survival of CRC, monthly 30-day mortality after surgery for CRC did not exhibit seasonal variation like that observed for comorbid conditions such as cardio-respiratory diseases.