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.