Prognostic Value of the Nodal Ratio and Ki-67 Expression in Breast Cancer Patients Treated with Postmastectomy Radiotherapy

PURPOSE This pilot study aimed to evaluate prognostic factors of postmastectomy radiotherapy (PMRT) for breast cancer patients undergoing systemic therapy in either preoperative or postoperative setting. METHODS Between 2003 and 2009, 113 patients received PMRT: 61 underwent preoperative systemic therapy (PST subgroup) and 52 received postoperative systemic therapy (non-PST subgroup). RESULTS The median follow-up time was 72.3 months (range, 34.0-109.4 months) for surviving patients. In univariate analysis of all patients, disease-free survival (DFS) was associated with age, nodal ratio (NR), and Ki-67 expression; overall survival (OS) was associated with NR and Ki-67 expression. Pathologic N stage and HER2 expression were marginally associated with DFS and OS. In the non-PST subgroup, DFS was associated with age, NR, venous invasion, and Ki-67 expression; OS was associated with age. In the PST subgroup, DFS was associated with ypN stage and NR; OS was associated with ypN, histologic grade, HER2 expression, and p53 expression. In multivariate analysis of all patients, DFS and OS were significantly associated with NR (p=0.003 and p=0.019, respectively) and Ki-67 expression (p=0.002 and p=0.015, respectively). Patients were classified into low-risk (NR ≤0.2 and Ki-67 ≤20%; n=34), intermediate-risk (NR >0.2 or Ki-67 >20%; n=63), and high-risk (NR >0.2 and Ki-67 >20%; n=16) subgroups. All low-risk patients were alive at the time of analysis. High-risk (p<0.001 and p=0.001, respectively) and intermediate-risk (p=0.022 and p=0.008, respectively) patients had significantly shorter DFS and OS than low-risk patients. This prognostic model was statistically significant for DFS when applied to the PST (p=0.001) and non-PST (p=0.016) subgroups separately. CONCLUSION For breast cancer patients undergoing PMRT, NR and Ki-67 are potential prognostic factors. A model using these factors might help predict a poor prognosis. Whether NR and Ki-67 are also prognostic for different setting of systemic therapy, preoperative or postoperative, warrants further study.