We identified three predictive factors for non-SN metastases in breast cancer patients with a positive SN: size of the SN metastasis; primary tumor size; and vessel invasion. We were not able to identify a specific group of patients with a positive SN in whom the risk for non-SN metastases was less than 5%.

Differences in SN pathology protocols between hospitals do have a substantial effect on SN findings and subsequent surgical treatment strategies. Whether ultrastaging and, thus, additional surgery can offer better survival remains to be determined.

The less intensified SN pathology protocol appeared to be associated with a slightly increased risk of regional recurrence. The absolute risk was still less than 3%, and does not seem to justify the intensified SN pathology protocol of hospital D.

Introduction of the new guideline considerably affected the number of patients eligible for adjuvant systemic therapy for breast cancer. The associated incremental cost-effectiveness ratio is well within the range of values that are generally considered acceptable.

Introduction of the SN procedure has led to the detection of more tumor-affected lymph nodes because of the intensified workup of SNs by pathologists. However, stage migration did not occur when tumor deposits of