Impact of omission of completion axillary lymph node dissection (cALND) or axillary radiotherapy (ax RT) in breast cancer patients with micrometastases (pN1mi) or isolated tumor cells (pN0[i+]) in the sentinel lymph node (SN): Results from the MIRROR study

CRA506 Background: The Dutch MIRROR study is the largest cohort study on pN1mi and pN0(i+) in the SN era with long-term follow-up, central pathology review (6th AJCC-classification), and separate analyses on the use of adjuvant systemic therapy (AST). In patients not receiving AST, pN1mi and pN0(i+) as final N-stage were shown to be independent prognosticators for disease-free survival (SABCS 2008, #23, oral). As a substantial number of patients in the MIRROR study did not undergo cALND or ax RT, we questioned whether this policy was safe in patients with pN1mi(sn) or pN0(i+)(sn). Methods: Patients operated for breast cancer in all Dutch hospitals in the years 1998–2005, having favorable primary tumor characteristics, and having undergone an SN biopsy without macrometastases as final N-stage were included. For this present research question, patients were categorized by their SN-stage. Median follow-up was 4.7 years. The Kaplan-Meier method was used to estimate 5-year axillary recurrence (AR) rates, and Cox regression was used to estimate the hazard ratios (HR). In the analyses, the effect of AST was taken into account. Results: In total, 835 patients with pN0(i-)(sn), 799 patients with pN0(i+)(sn), and 958 patients with pN1mi(sn) were included. AR rates, and HRs on AR are displayed below. Conclusions: Omission of cALND or ax RT in patients with pN1mi(sn) resulted in a significantly higher 5-year AR rate, even after correction for AST, and other patient and tumor characteristics. This indicates that patients with pN1mi(sn) should undergo cALND or ax RT to prevent AR. Support: The Netherlands Organization for Health Research and Development (ZonMw) and the Dutch Breast Cancer Trialists’ Group (BOOG). n 5-year AR(%) HR AR (95%CI)* pN0(i-)(sn) cALND 113 1.9 1.00 pN0(i-)(sn) SN 722 2.2 1.07 (0.23 - 4.94) pN0(i+)(sn) cALND or ax RT 459 1.1 1.00 pN0(i+)(sn) SN 340 1.7 2.14 (0.57 - 7.96) pN1mi(sn) cALND or ax RT 828 1.2 1.00 pN1mi(sn) SN 130 6.2 4.45 (1.46 - 13.54) * Corrected for AST, age, (log) tumor size, grade, hormone receptor status. No significant financial relationships to disclose.