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Purpose: Interpectoral lymph nodes (IPNs) are one of the lymphatic drainage pathways in breast cancer. However, the clinical significance of IPN dissection is controversial, and there is no international consensus regarding the management of IPN for resectable breast cancer. Our study aims to identify the independent predictors of IPN metastasis in invasive breast cancer (IBC) and provide some evidence for rational decision-making. Methods: Data from 214 IBC patients who were treated with modified radical mastectomy (MRM) plus IPN dissection or biopsy in Ningbo Medical Center Lihuili Hospital were retrospectively reviewed. Univariate analysis and multivariate logistic regression analysis were used to analyse the correlations between IPN occurrence or metastasis and clinicopathological characteristics. Results: The occurrence rate of IPN in overall population was 75.2%. Univariate analysis showed that tumour size, involvement of axillary lymph nodes (ALNs), histological grading, Ki67 index and molecular subtype were associated with the occurrence of IPN. However, involvement of ALN was the only independent predictor by multivariate logistic regression analysis. In 161 patients whose IPNs were detected, 46 (28.6%) patients had one or more metastatic IPNs. Univariate analysis showed that tumour size, involvement of ALN, oestrogen receptor status and molecular subtype were associated with IPN metastasis. However, involvement of ALN was the only predictor by multivariate logistic regression analysis. In total, 0%, 5.0%, 26.1% and 84.2% of pN0, pN1, pN2, and pN3 patients had metastatic IPNs, respectively. Conclusion: The relatively low rate of IPN metastasis in patients with pN0/N1 breast cancer suggests that IPN dissection can be safely spared in patients with low tumour burden in axillary lymph nodes (pN0/N1), when MRM even breast conservation surgery is performed. [ABSTRACT FROM AUTHOR]