Does the introduction of sentinel node biopsy increase the number of node positive patients with early breast cancer? A population based study form the Danish Breast Cancer Cooperative Group.

Background: The validation series of sentinel lymph node biopsy (SLNB) in the treatment of breast cancer have shown that 10-20% more lymph node metastases are detected. However, their impact has never been studied in populations where the method has been fully implemented. In a population-based setting, the objective of the current study was to estimate the increased risk of metastases after introduction of the sentinel lymph node biopsy technique.
Methods: We identified all new breast cancer patients in three different counties in two time periods (1996-1997 and 2002-2003). The study cohort was comprised of 2 932 patients. The main outcome was the frequency of patients with metastases. The frequencies of patients with metastases were compared as well as adjusted (using a multivariate logistic regression) and unadjusted odds-ratio for detecting lymph node metastases.
Results: In counties where sentinel lymph node biopsy was implemented, the frequency of patients with lymph node metastases increased significantly 7.3% (95% CI: 1.0-13.7%) and 13.3% (95% CI: 7.3-19.3%), respectively. In the county without sentinel lymph node biopsy, an insignificant increase of 6.9% (-0.1-13.9%) in the frequency of patients with metastases was seen. The adjusted odds- ratio for detecting lymph node metastases was 1.41 (1.07-1.87) and 1.70 (1.30-2.23) in the counties with SLNB.
Conclusion: The frequency of patients with metastases increased significantly in counties where sentinel lymph node biopsy was implemented.