Incorporation of biological risk into the eighth edition of AJCC TNM staging system
With the TNM-stratified analysis, there was no significant survival difference between low-risk group and middle-risk group in stage I, while the OS of the two groups was significantly better than that of high-risk group in stage I (Figure 4,A ). Of the patients in stage II, the survival differences were significant between each two groups (Figure 4,B ). Of the pateints in stage III, there was no significant survival difference among the three groups (Figure 4,C ). The OS of patients in low-risk and middle-risk group, who were at stage I was similar to that of patients in low-risk group who were at stage II. The OS of patients in high-risk group who were at stage I was similar to that of patients in middle-risk group who were at stage II. The OS of patients in high-risk group who were at stage II was similar to that of patients in stage III(Figure 4,D ).
According to the results of the strata analysis, we incorporated the biological risk into the eighth edition of the TNM staging system and introduced our modified TNM (mTNM) staging system (TableIV ). In the mTNM staging system, the 5-year OS rates of stage mI, mII and mIII were 31.5%, 17.2% and 7.2%, respectively (χ2=78.603, P <0.001). In the TNM staging system, the 5-year OS rates of stage I, II and III were 28.2%, 14.9% and 7.7%, respectively (χ2=37.794, P <0.001) (Table V, Figure 5 A,B ). Then, the mTNM stage and the factors associated with OS in the univariate analysis were included in the multivariate analysis again. This time, age at surgery, postoperative adjuvant chemotherapy and mTNM stage were found to be independent prognostic factors for OS. The, biological risk and TNM stage were not significant in the multivariate analysis (Table III ).