Evaluation of prognostic factors effect on survival time in patients with colorectal cancer, based on Weibull Competing-Risks Model

Aim: The aim of this study was to assess the association between survival of patients with colorectal cancer and prognostic factors in a competing risks parametric model using Weibull distribution. Background: The prognosis of colorectal cancer is relatively good in terms of survival time. In many prognostic studies, patients may be exposed to several types of competing events. These different causes of death are called competing risks. Methods: Data recorded from 372 patients with colorectal cancer who registered in Institute for Gastroenterology and Liver Diseases, Shahid Beheshti University of Medical Sciences (Tehran, Iran) from 2004 to 2015 in a retrospective study. Analysis was performed using competing risks model and Weibull distribution. Software used for data analysis was R, and significance level was regarded as 0.05. Results: The result indicated that, at the end of follow-up, 111 (29.8%) death was from colorectal cancer and 14 (3.8%) death was due to other diseases. The average body mass index (BMI) was 24.61(SD 3.98). The mean survival time for a patient in 372 was 62.05(SD 48.78) month with median equals to 48 months. According to competing-risks method, only stageIII ( HR, 1.69; 95% CI, 1.246-2.315 ), stageIV( HR, 4.51; 95% CI,2.91-6.99 ) and BMI( HR, 0.96; 95% CI, 0.96-0.975) have a significant effect on patient’s survival time. Conclusion: This study indicated pathologic stage(III,IV) and BMI as the prognosis, using Weibull model with competing risks analysis, while other model without the competing events leads to significant predictors which may due to over-estimation.