OBJECTIVE: To investigate the risk factors for residual axillary lymph node macro-metastasis in early-stage breast cancer patients with a single macrometastasis sentinel lymph node (SLN). METHODS: We retrospectively analyzed the clinical data of 119 breast cancer patients diagnosed between January 2018 and September 2023, each with one positive SLN stained with methylene blue, who subsequently underwent axillary lymph node dissection. The patients were divided into two groups based on the total number of SLNs identified: fewer than three and more than three. Fisher's exact test was used for statistical analysis between groups. RESULTS: Among the 119 patients evaluated, 30 patients had a total of 2 sentinel lymph nodes, with 15 testing positive for residual axillary lymph nodes, yielding a positivity rate of 50.0%. Another 30 patients had 3 sentinel lymph nodes, with a positivity rate of 33.3%. An additional 32 patients each had 4 sentinel lymph nodes, with a positivity rate of 3.13%. Finally, 27 patients had 5 sentinel lymph nodes, with a 0% positivity rate. The positivity rate of axillary lymph nodes was significantly higher in the group with ≤ 3 sentinel lymph nodes (less SLN group) compared to the group with >
4 sentinel lymph nodes (more SLN group). Binary logistic regression analysis confirmed that the number of SLNs was the only significant predictor of residual lymph node macrometastasis. CONCLUSION: The number of sentinel lymph nodes (SLNs) is a key factor influencing the risk of residual axillary lymph node macrometastasis in early-stage breast cancer patients with one positive SLN. Identifying a higher number of SLNs (≥4) significantly lowers the risk of residual metastasis, supporting the use of thorough SLN mapping in these cases to improve patient outcomes.