Prognostic implication of the tumor location according to molecular subtypes in axillary lymph node-positive invasive ductal cancer in a Korean population

Previous studies have not considered the axillary lymph node status when investigating the prognostic role of tumor location according to each molecular subtype. The present study aimed to investigate the prognostic implication of tumor location according to each molecular subtype in Korean invasive ductal carcinoma (IDC) patients with axillary lymph node metastasis. Data from 7856 Korean IDC women with axillary lymph node metastasis were retrospectively analyzed. According to tumor location, patients were divided into the following groups: upper-outer quadrant, lower-outer quadrant, upper-inner quadrant, lower-inner quadrant (LIQ), and central group. Overall survival (OS) and breast cancer-specific survival (BCSS) were evaluated according to tumor location and molecular subtype. A subgroup analysis based on tumor size categorization was also performed. The patients’ mean age was 47.97 ± 9.64 years, and the median follow-up time was 90 months. The LIQ group showed significantly worse prognosis in OS and BCSS (76.4 and 83.3 %, respectively) compared with the other groups, which was only significant in human epidermal growth factor receptor 2 (HER2) overexpression and triple-negative (TN) subtypes. In the subgroup analysis according to tumor size, the LIQ group showed a significantly worse prognosis in OS and BCSS compared with the other groups, in HER2 and TN subtypes, and only in patients with more than T2 stage. In Korean IDC patients with axillary lymph node metastasis, LIQ tumor location was associated with poor prognosis among those with HER2 and TN molecular subtypes and especially in those with more than T2 stage.