Effects of postmastectomy radiotherapy on prognosis in different tumor stages of breast cancer patients with positive axillary lymph nodes

Objective: To explore the effects of postmastectomy radiotherapy(PMRT) on the locoregional failure-free survival(LRFFS) and overall survival(OS) of breast cancer patients under different tumor stages and with one to three positive axillary lymph nodes(ALNs). Methods: We conducted a retrospective review of 527 patients with one to three positive lymph nodes who underwent modified radical or partial mastectomy and axillary dissection from January 2000 to December 2002. The patients were divided into the T1-T2 N1 and T3-T4 N1 groups. The effects of PMRT on the LRFFS and OS of these two patient groups were analyzed using SPSS 19.0, Pearson's χ2-test, Kaplan-Meier method, and Cox proportional hazard model. Results: For T1-T2 N1 patients, no statistical significance was observed in the effects of PMRT on LRFFS [hazard ratio(HR)=0.726; 95% confidence interval(CI): 0.233-2.265; P=0.582] and OS(HR=0.914; 95% CI: 0.478-1.745; P=0.784) of the general patients. Extracapsular extension(ECE) and high histological grade were the risk factors for LRFFS and OS with statistical significance in multivariate analysis. Stratification analysis showed that PMRT statistically improved the clinical outcomes in high-risk patients [ECE(+), LRFFS: P=0.026, OS: P=0.007; histological grade III, LRFFS: P<0.001, OS: P=0.007] but not in low-risk patients [ECE(–), LRFFS: P=0.987, OS: P=0.502; histological grade I-II, LRFFS: P=0.816, OS: P=0.296]. For T3-T4 N1 patients, PMRT effectively improved the local control(HR=0.089; 95% CI: 0.210-0.378; P=0.001) of the general patients, whereas no statistical effect was observed on OS(HR=1.251; 95% CI: 0.597-2.622; P=0.552). Absence of estrogen receptors and progesterone receptors(ER/PR)(–) was an independent risk factor. Further stratification analysis indicated a statistical difference in LRFFS and OS between the high-risk patients with ER/PR(–) receiving PMRT and not receiving PMRT [ER/PR(–), LRFFS: P=0.046, OS: P=0.039]. However, PMRT had a beneficial effect on the reduction of locoregional recurrence(LRR) but not in total mortality [ER/PR(+), LRFFS: P<0.001, OS: P= 0.695] in T3-T4 N1 patients with ER/PR(+) who received endocrine therapy. Conclusion: PMRT could reduce ECE(+), histological grade III-related LRR, and total mortality of T1-T2 N1 patients. T3-T4 N1 patients with ER/PR(–) could benefit from PMRT by improving LRFFS and OS. However, PMRT could only reduce LRR but failed to improve OS for T3-T4 N1 patients with ER/PR(+) who received endocrine therapy.