Background: The prognostic implication of tumor location in breast cancer remains unclear. Previous studies suggested that inner and lower quadrant-located tumors were associated with decreased survival.
Methods: The NCDB was quired to identify AJCC clinical stage I-III first female breast cancer patients with unilateral disease who underwent breast-conserving surgery from 2010 to 2016. Three mutually exclusive groups were created based on tumor location, which included outer (upper and lower outer quadrants), central, and inner (upper and lower inner quadrants) zones of the breast. Clinical and demographic variables were obtained. Unadjusted survival differences were examined with Kaplan- Meier method. Multivariate Cox regression model was employed to examine the association between zone group and survival.
Results: 125,800 patients were identified including 83,558 (66.4%), 6,764 (5.4%), and 35,449 (28.2%) patients within the outer, central, and inner zones. There was evidence of a difference in age and tumor size based on site (P<0.001). It was also found that there was an association between tumor zone and each of the following (P<0.05): race and ethnicity, Charlson-Deyo score, insurance, income, education, facility type, laterality, histology, utilization of chemotherapy, ER status, PR status, and HER2 status. There was no relationship between site and unadjusted survival (P=0.905). After adjusting for all else, a 5.7% decreased the risk of death was found upon the comparison of the outer vs. inner zone of the breast (95% CI: 0.4%-11.8%; P=0.037). In general, older African American Medicaid patients with increased Charlson-Deyo scores and hormone receptor-negative breast cancers from lower-income areas had decreased survival.
Conclusion: Outer zone breast cancer has a more favorable survival advantage when compared with inner zone cancers. A finding that warrants re-evaluation of the management approach to inner zone breast cancer.