Abstract RF2-01: Prognostic Markers in Residual Tumors after neoadjuvant chemotherapy (NACT) for Early Triple-negative Breast Cancer (TNBC) - a Pooled Analysis from nine Neoadjuvant GBG/AGO-B Trials

Abstract Background: Residual invasive disease after NACT for TNBC is associated with high recurrence rates and poor overall survival (OS). The assessment of pathologic complete response (pCR) vs. non-pCR in early breast cancer is not consistently linked to OS. For instance, it does not address partial responses or favourable changes in tumor biology during NACT. Therefore, we investigated proliferation (Ki67) and tumor-infiltrating lymphocytes (TILs) in invasive residual tumor (RT) for improved prediction of outcome. Study Design: Pts with TNBC treated with anthracycline/taxane-containing NACT in nine GBG/AGO-B trials (GeparTrio, GeparQuattro, GeparQuinto, GeparSixto, GeparSepto, GeparOcto, GeparNuevo, GeparOla, and GeparX) were included. Of 3017 pts with TNBC enrolled, 1505 had ypT>0/is and 640 had prospectively collected RT-samples for evaluation of TILs and Ki67. Endpoints were distant disease-free survival (DDFS; primary endpoint) and OS (both as land-mark analysis). Results: Of the 640 pts included, most had cT2 (57.6%), 36.9% had cN+ with 61.6% having stage II disease. At baseline (BL), 93.4% of tumors had Ki67>15% (median 51%), the median for TILs at BL was 20%. After treatment, 54% of RTs had Ki67>15% (median 18%) with a median absolute change in Ki67 of -27.5% compared to BL. Median TILs in RT were 20% with a median change of +5% compared to BL. In pts with ypT1, ypN0 at surgery Ki67 was lower and TILs were higher in RT compared to pts with >ypT1y, pN0 at surgery with no correlation with ypN status. Ki67 >15% vs ≤15% in RT was associated with worse DDFS (HR 1.71; 95% CI 1.33-2.21; p