Development of biological risk model
Initially, all patients were categorized into four groups according to the levels of preoperative serum CA19-9 and histology grade: group 1, CA19-9≤112 U/ml and low grade; group 2, CA19-9≤112 U/ml and high grade; group 3, CA19-9>112 U/ml and low grade; group 4, CA19-9>112 U/ml and high grade. The 5-year OS rates were 28.5, 23.0, 18.6 and 11.9% in group 1, 2, 3 and 4, respectively. There was no survival difference between group 2 and group 3 (5-year OS: 23.0% vs 18.6%, P=0.805) (Figure 3, A ).
Peroperative serum CA19-9 and histology grade were used to build a biological risk (BR) score taking into account of their hazard ratios in the multivariate analysis. Patients with preoperative serum CA19-9 ≤112 U/ml and low grade were given a BR score of 0. Patients with preoperative CA19-9>112U/ml and low grade as well as those with preoperative serum CA19-9 ≤112 U/ml and high grade were given a BR score of 1. Patients with preoperative CA19-9>112U/ml and high grade were given a BR score of 2. The BR score was 0 for 129 patients, 1 for 267 patients and 2 for 216 patients, respectively. Patients were divided into three groups according to the BR score: low risk group (BR=0), middle risk group (BR=1) and high risk group (BR=2). The 5-year OS rates were 28.5%, 14.9% and 7.7% for patients in the low-risk group, middle-risk group and high-risk group, respectively (χ2=92.762, P<0.001)(Figure 3, B ). In the multivariate analysis, the BR score was an independent prognosis factor for OS (HR was 1.342, P=0.047). Preoperative serum CA19-9 and histology grade were not significant if the BR score was included in the multivariate analysis (Table III ).