Survival analysis of postmastectomy radiotherapy for breast cancer staged in cT1-2N1M0 after neoadjuvant chemotherapy with 0-3 metastatic lymph nodes

Objective To investigate the value of postoperative radiotherapy in patients with cT1-2N1M0 breast cancer after neoadjuvant chemotherapy and modified radical mastectomy which postoperative pathology showed that the number of axillary lymph node metastases was 0-3. Methods One hundred and twenty-eight patients diagnosed with cT1-2N1M0 breast cancer admitted to our hospital from January 1, 2000 to December 31, 2014 were retrospectively reviewed. All patients underwent neoadjuvant chemotherapy and modified radical mastectomy. The number of postoperative axillary lymph node metastases was 0-3. According to whether there was postoperative radiotherapy or not, the whole group of patients was divided into radiotherapy group (n=87) and non-radiotherapy group (n=41). In the two groups after operation, there were 43 and 11 patients with 1-3 axillary lymph node metastases (ypN1), while there were 44 and 30 patients without axillary lymph node metastases (ypN0) respectively. The 5-year locoregional recurrence-free survival (LRFS) rate, disease-free survival (DFS) rate and overall survival (OS) rate were calculated by Kaplan-Meier method, and the differences were compared by log-rank test. Univariate analysis was performed to analyze the effects of clinical features and treatment on prognosis. Results The 5-year LRFS rate, DFS rate and OS rate of 128 patients were 91.4%, 82.8% and 93.0% respectively. The 5-year LRFS rates of the patients in the radiotherapy group and the non-radiotherapy group were 94.3% and 85.4% respectively, and the difference was not statistically significant (χ2=3.055, P=0.080). As well as the 5-year DFS rates were 89.7% and 68.3% respectively, and the difference was statistically significant (χ2=9.312, P=0.005). The 5-year OS rates were 94.3% and 90.2% respectively, and the difference was not statistically significant (χ2=0.810, P=0.368). In the subgroup analysis, the 5-year LRFS rates of the patients who had achieved ypN1 in the radiotherapy group and the non-radiotherapy group were 93.0% and 72.7%, and the 5-year DFS rates were 88.4% and 63.6%, with statistically significant differences (χ2=4.248, P=0.039; χ2=4.525, P=0.033). The 5-year OS rates were 90.7% and 81.8% respectively, and the difference was not statistically significant (χ2=0.713, P=0.399). The 5-year LRFS rates of the patients who had achieved ypN0 in the radiotherapy group and the non-radiotherapy group were 95.5% and 90.0% respectively, with no statistically significant difference (χ2=0.872, P=0.350). The 5-year DFS rates were 90.9% and 70.0% respectively, with statistically significant difference (χ2=5.439, P=0.019). The 5-year OS rates were 97.7% and 93.3% respectively, with no statistically significant difference (χ2=0.876, P=0.349). The univariate analysis indicated that age (χ2=11.709, P=0.001) and blood vessel invasion (χ2=7.608, P=0.006) were significant influencing factors for 5-year LRFS rate. Postoperative radiotherapy (χ2=9.312, P=0.002) was a prognostic factor for 5-year DFS rate. Age (χ2=6.093, P=0.014) and hormone receptor status (χ2=3.974, P=0.046) were prognostic factors for OS. Conclusion For the cT1-2N1M0 breast cancer patients with 1-3 positive axillary lymph nodes after neoadjuvant chemotherapy, postmastectomy radiotherapy has local control benefit, and it can improve DFS. However, the benefit of postoperative radiotherapy needs to be further investigated in patients with pathological negative axillary lymph nodes after neoadjuvant chemotherapy. Key words: Breast neoplasms; Prognosis; Neoadjuvant chemotherapy; Radiotherapy