Micrometastases and isolated tumor cells: relevant and robust or rubbish? (MIRROR): preliminary results of the MIRROR study from the Dutch breast cancer trialists' group (BOOG).

CTRC-AACR San Antonio Breast Cancer Symposium: 2008 Abstracts Abstract #23 Background The sentinel lymph node procedure (SNP) has largely replaced axillary lymph node dissection (ALND) in patients with early breast cancer (BC). Intensified examination of the sentinel node (SN) results in the detection of isolated tumor cells (ITCs) and micrometastases, whereas its relevance is still debated. This retrospective cohort study is the first study on this topic which includes only patients who underwent a SNP, with central review of all SN slides, and with separate analyses for the impact of administration of adjuvant systemic therapy. Methods Patients operated for BC in all Dutch hospitals in the years 1998-2005, having favourable tumor characteristics (> 35 year; tumor size 1-3 cm and differentiation grade I-II OR tumor size ≤ 1 cm irrespective of grade), having undergone a SNP with pN0(i-), pN0(i+), or pN1mi as final N-stage were selected. Patients were classified in cohort I in case of pN0(i-) and no adjuvant systemic therapy (AST), in cohort II in case of pN0(i+)/pN1mi and no AST, and in cohort III in case of pN0(i+)/pN1mi with AST. SNs were centrally reviewed and restaged according to 6th TNM classification. The 5-year disease-free survival (DFS) was analysed for the 3 different cohorts. Results So far, data are available for 1,744 of the 3,240 selected patients (cohort I n=935; cohort II n=340, cohort III n=469) with a median follow-up of 5.5 years. At diagnosis median age was 58, 56 and 56 years (p < 0.01) and median tumor size was 1.2, 1.4 and 1.5 cm (p < 0.0001). Differentiation grade and hormone receptor status were equally distributed among the three cohorts. Adjuvant systemic therapy in cohort III consisted of chemotherapy (10%), hormonal therapy (63%), or both (27%). The 5-yr DFS is 84% in cohort I, 73% in cohort II, and 86% in cohort III (p = 0.003 cohort I vs II; p < 0.0001 cohort II vs III). Correction for baseline characteristics did not lead to a relevant change in the results. Conclusion BC patients with ITCs or micrometastases as final N-stage after SNP have a significantly worse 5-yr DFS as compared to patients having no ITCs or micrometastases, independent of primary tumor characteristics. Adjuvant systemic therapy significantly improves the 5-yr DFS in the group of patients with ITCs or micrometastases in the lymph node(s). At the meeting, updated analyses will be available for the entire MIRROR study population. Support: The Netherlands organization for health research and development (ZonMw) and all Dutch CCCs. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 23.