L. A. Riba1, T. A. James1 1Beth Israel Deaconess Medical Center,Surgery,Boston, MA, USA
Introduction: Sentinel lymph node biopsy (SLNB) is recognized as a safe and efficient method for axillary node evaluation in clinically node negative patients with breast cancer. Although developed as a less invasive alternative to axillary lymph node dissection (ALND), SLNB is not free of risks, added costs and patient discomfort. Furthermore, data have already begun to identify subsets of low-risk patients where SLNB may not be required (i.e. women over 70 with hormone receptor positive breast cancer). The purpose of this study was to determine if there were additional low risk subsets were this procedure may be safely omitted because of a low rate of axillary node involvement.
Methods: This is a retrospective study using data from the National Cancer Database. The population consisted of female patients with pathological T1-T2 primary invasive ductal carcinoma (IDC) who underwent a SLNB between 2012 and 2014. Descriptive statistics were used to analyze the main characteristics of the study population and determine the rate of node positivity related to each clinically relevant characteristic. These clinically relevant characteristics, including age group, ethnicity, tumor grade, tumor size (using pathologic TNM classification) and tumor receptor status, were then used in a multivariate logistic regression, modeling for negative nodes following SLNB. From the multivariate regression model we obtained odds ratios and 95% confidence intervals for each variable as an indicator of negative SLNB.
Results: Our study population consisted of 114,916 women who underwent SLNB, of which 79.37% had negative nodes and 20.63% had positive nodes. Multivariate logistic regression analysis found a significant relationship between a negative SLNB result and older age, Asian ethnicity, tumor size smaller than 20mm and triple negative tumor receptor status. Small tumor size was found to be the strongest indicator of negative SLNB, particularly microinvasive tumors (OR, 8.29; 92% negative SLNB), pT1A tumors (OR, 11.11; 94% negative SLNB), pT1B tumors (OR, 6.28; 91% negative SLNB), and pT1C tumors (OR 2.36; 79% negative SLNB). Older age was also associated with increased negative SLNB rates, with the 65 to 79 age group presenting 84% negative SLNB (OR, 2.18) and the over 80 age group with 81% negative SLNB (OR, 2.07). Other factors found to present a significantly higher negative SLNB rates are triple negative breast tumors (OR = 1.83; 83% negative SLNB) and Asian ethnicity (OR = 1.62, 81% negative SLNB).
Conclusion: Our results show breast cancer subpopulations with significantly decreased risk of axillary involvement, for which the use of SLNB could be safely omitted under the appropriate circumstances. This may have implications for surgical decision-making in cases of micro-invasion, and small invasive breast cancers found following excisional biopsy, especially in elderly patients.