Association between breast cancer located in the upper outer quadrant (UOQ) and axillary lymph node metastasis (N1 disease): Clinical implications and prognostic significance.

Abstract

e12764 Background: While tumor location influences lymphatic drainage patterns, its prognostic value in node-positive disease is unknown. We evaluated whether upper outer quadrant (UOQ) tumor location is associated with distinct survival outcomes in patients with N1 breast cancer. Methods: We conducted a retrospective cohort study of 1,914 breast cancer patients with N1 disease treated at Seoul National University Hospital between January 2000 and December 2020. N1 disease was defined as biopsy-confirmed clinical N1 in neoadjuvant chemotherapy recipients or pathologic N1 in upfront surgery patients. Tumor location was determined by preoperative imaging (ultrasonography and MRI). Distant metastasis-free survival (DMFS) and overall survival (OS) were analyzed using Kaplan-Meier and Cox proportional hazards models. Results: Among enrolled patients, 938 (49.0%) had UOQ tumors and 976 (51.0%) had non-UOQ tumors. While UOQ patients were older (median 49 vs 47, p-value 0.004) and received breast-conserving surgery and radiotherapy more frequently (58.6% vs 44.8, p-value < 0.001), tumor stage, molecular subtype, histologic grade, and systemic treatment were comparable between groups. In this node-positive cohort, UOQ location was associated with significantly superior 5-year DMFS (86.3% vs 75.3%, p < 0.001) and OS (93.4% vs 87.9%, p < 0.001). On multivariate analysis, UOQ location remained a significant independent favorable prognostic factor, reducing the risk of distant metastasis by 50% (HR 0.50, 95% CI 0.42–0.60, p < 0.001) and death by 47% (HR 0.53, 95% CI 0.42–0.66, p < 0.001) after adjusting for tumor stage, molecular subtype, histologic grade. Conclusions: Among patients with node-positive breast cancer, UOQ tumor location confers a substantial survival advantage independent of conventional prognostic factors. This finding suggests that nodal positivity has a less adverse prognostic impact when the primary tumor is located in the UOQ, potentially reflecting distinct patterns of lymphatic spread. Tumor location might be incorporated into risk stratification for N1 breast cancer patients.