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.
Keywords: Breast neoplasms; Ki-67 antigen; Lymph nodes; Mastectomy; Radiotherapy.