Axillary lymph node metastasis status and associated factors in patients with breast cancer undergoing radical surgery.

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Background: Breast cancer remains one of the most frequently diagnosed malignancies and a leading cause of cancer-related mortality worldwide. According to GLOBOCAN 2022, it ranks second in incidence with more than 2.2 million new cases, following lung cancer, and fourth in global cancer mortality. Lymphatic dissemination represents the principal pathway of metastasis in breast cancer; therefore, accurate assessment of axillary lymph node status is essential for staging, prognostication, and therapeutic decision-making. Currently, nodal metastasis is primarily diagnosed based on routine hematoxylin and eosin (H&E) staining. However, accumulating evidence indicates that certain metastatic deposits, particularly micrometastases, may be overlooked when evaluated solely by conventional H&E staining. The application of immunohistochemistry (IHC) has enhanced the detection of these occult nodal micrometastases. To date, no study has investigated the characteristics of axillary lymph node micrometastasis in breast cancer patients at our institution. Objective: This study aimed to describe the characteristics of axillary lymph node micrometastasis detected by immunohistochemistry but not identified by routine H&E staining, and to explore associated clinicopathological factors in breast cancer patients undergoing radical surgery. Methods: A retrospective descriptive study was conducted on 56 breast cancer patients with stage pT any/N0M0 who underwent radical surgery at Hanoi Medical University Hospital between January 2021 and August 2025. Results: IHC staining identified lymph node micrometastases in 4 out of 56 patients (7.14%). No statistically significant associations were found between micrometastases and estrogen receptor, progesterone receptor, HER2 status, Ki67 index, vascular invasion, perineural invasion, or tumor size. Among the 4 patients with micrometastases, 3 received additional adjuvant radiotherapy following the detection by IHC. Conclusions: The rate of lymph node micrometastases detected by IHC in this study was 7.14%. Immunohistochemical staining improves the detection of micrometastases compared to conventional HE staining, and may influence adjuvant treatment strategies in breast cancer patients.