Background: In 2003, the American Joint Committee on Cancer (AJCC) initiated the 6th edition staging criteria, including pN0(i+) and pN1mi categories for breast cancer. However, the clinical significance of these categories is debated in the literature.
Methods: A prospective registry was used to identify patients staged with sentinel lymph node (SLN) biopsy. SLN evaluation included routine serial sectioning and immunohistochemical stains. SLN biopsies performed before January 2003 were restaged according to the AJCC's 6th edition criteria.
Results: Of 954 SLN biopsies identified, on review, 491 N0i-, 86 N0i+, 73 N1mi, 146 N1a, 29 N2a, and 11 N3a patients were available for analysis with a median follow-up of 45.4 months. Significant prognostic and therapeutic differences existed between the groups. Differences in overall survival (OS) and recurrence-free survival (RFS) were only noted when the size of the metastases reached the N1a level. There were no statistically significant differences in OS or RFS between N0(i-) and N0(i+) or N1mi disease. Cases that were N0(i+) or N1mi were more likely to have other poor prognostic factors and to receive more aggressive therapy.
Conclusion: SLN biopsy allows a more sensitive evaluation of lymph nodes for metastatic cells. This has led to the increased identification of very small axillary metastases. While the new microstaging categories are not yet clearly associated with a significantly decreased OS or DFS in this series, they are associated with other poor prognostic factors and more local/regional and systemic therapy. Further analysis of the microstaging categories is needed.