Preoperative axillary US and MRI in early-stage breast cancer: Potential to prevent unnecessary axillary surgery.

577 Background: Recent studies, including the INSEMA and SOUND trials, have demonstrated that omitting sentinel lymph node (SLN) biopsy does not adversely affect survival outcomes. Notably, patients with positive axillary findings on ultrasound (US) tended to show more extensive axillary nodal metastasis on final histopathological examination. Thus, we aimed to focused on the advanced utility of preoperative axillary US and Magnetic Resonance Imaging (MRI) in preventing unnecessary axillary surgery in a large series of patients with early-stage breast cancer treated with both breast surgery and SLN biopsy. Methods: Between January 2012 to December 2023, a total of 7879 patients who underwent breast surgery for clinical T1–2/N0 cancers and SLN biopsy with or without axillary lymph node dissection were included. Preoperative axillary US and MRI findings were compared with clinical-pathologic variables, considering the presence of SLN metastasis. Patients with positive results routinely underwent US-guided fine needle aspiration biopsy (FNAB), and negative FNAB results were also considered. Multivariate logistic regression analysis was used to identify factors associated with SLN metastasis. Results: A total of 7879 eligible patients (47.48% with clinical T1 cancer and 52.52% with T2 cancer) were included in our study. Among them, 2048 (25.99%) had positive SLN biopsy, and 1971 (25.02%) underwent axillary lymph node dissection due to positive SLN biopsy. Patients with SLN metastasis were younger and had a higher frequency of positive axillary findings on US and MRI, as well as clinical T2 stage (P<0.05). At multivariate analysis, positive axilla at US (P =0.001), positive axilla at MRI (P =0.02), clinical T2 stage (P =0.004), grade 3 (P =0.004) and lymphovascular invasion (P=0.001) were significantly associated with SLN metastasis. The number of nodal metastases increase with increasing tumor size. Among 3595 (45.06%) patients with negative axilla at US and MRI and clinical T1 stage cancer, 698 (8.75%) had SLN metastasis. For these people, the median follow-up was 73.6 months. The estimated 5-year invasive disease–free survival rate was 96.8%, while the 5-year overall survival rate was 98.6%. The analysis of the first primary-outcome events (occurrence or recurrence of invasive disease or death from any cause), showed apparent differences between the positive axilla at US and MRI and clinical T1 stage cancer group and negative axilla at US and MRI and clinical T1 stage cancer group in the incidence of recurrence (4.7% vs. 3.2%) and death (2.0% vs. 1.4%). Conclusions: Preoperative axillary US and MRI results, along with clinical T stage are significant predictors of SLN metastasis in patients with early-stage breast cancer. The results of this study suggest that preoperative axillary US and MRI can help select patients at minimal risk of SLN metastasis, for whom axillary surgery could be omitted.