Number of negative lymph nodes can predict survival of breast cancer patients with four or more positive lymph nodes after postmastectomy radiotherapy

BACKGROUND: This study was conducted to assess the prognostic value of the number of negative lymph nodes (NLNs) in breast cancer patients with four or more positive lymph nodes after postmastectomy radiotherapy (PMRT). METHODS: This retrospective study examined 605 breast cancer patients with four or more positive lymph nodes who underwent mastectomy. A total of 371 patients underwent PMRT. The prognostic value of the NLN count in patients with and without PMRT was analyzed. The log-rank test was used to compare survival curves, and Cox regression analysis was performed to identify prognostic factors. RESULTS: The median follow-up was 54 months, and the overall 8-year locoregional recurrence-free survival (LRFS), distant metastasis-free survival (DMFS), disease-free survival (DFS), and overall survival (OS) were 79.8%, 50.0%, 46.8%, and 57.9%, respectively. The optimal cut-off points for NLN count was 12. Univariate analysis showed that the number of NLNs, lymph node ratio (LNR) and pN stage predicted the LRFS of non-PMRT patients (p < 0.05 for all). Multivariate analysis showed that the number of NLNs was an independent prognostic factor affecting the LRFS, patients with a higher number of NLNs had a better LRFS (hazard ratio = 0.132, 95% confidence interval = 0.032-0.547, p =0.005). LNR and pN stage had no effect on LRFS. PMRT improved the LRFS (p < 0.001), DMFS (p = 0.018), DFS (p = 0.001), and OS (p = 0.008) of patients with 12 or fewer NLNs, but it did not any effect on survival of patients with more than 12 NLNs. PMRT improved the regional lymph node recurrence-free survival (p < 0.001) but not the chest wall recurrence-free survival (p = 0.221) in patients with 12 or fewer NLNs. CONCLUSIONS: The number of NLNs can predict the survival of breast cancer patients with four or more positive lymph nodes after PMRT. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13014-014-0284-5) contains supplementary material, which is available to authorized users.