Options of locoregional therapy for primary foci of breast cancer influence the rate of nonregional lymph node metastasis in N2-N3 status patients: a SEER database analysis.

Objective: We aim to use the SEER database to discuss the effect of various surgical methods of primary foci and other influencing factors on the nonregional lymph node (NRLN) metastasis in invasive ductal carcinoma (IDC) patients.

Methods: Clinical information of IDC patients used in this study was obtained from the SEER database. The statistical analyses used included a multivariate logistic regression model, the chi-squared test, log-rank test and propensity score matching (PSM).

Results: 243,533 patients were included in the analysis. 94.3% of NRLN patients had a high N positivity (N3) but an equal distribution in T status. The proportion of operation type, especially BCM and MRM, differed significantly between the N0-N1 and N2-N3 groups in the NRLN metastasis group and nonmetastasis group. Age > 80 years, positive PR, modified radical mastectomy (MRM)/radical mastectomy (RM) and radiotherapy for primary tumor were shown to be protective factors for NRLN metastasis, and higher N positivity was the most significant risk factors. N2-N3 patients receiving MRM had a lower metastasis to NRLN than those receiving BCM (1.4% vs 3.7%, P < 0.001), while this relevance was not discovered in N0-N1 patients. In N2-N3 patients, a better OS was observed in MRM group than BCM group (P < 0.001).

Conclusion: MRM exerted a protective effect on NRLN metastasis compared to BCM in N2-N3 patients but not N0-N1 patients. This implies the need for more consideration when choosing the operation methods of primary foci in patients with high N positivity.