Abstract P2-16-24: Impact of pathologic complete response (pCR) and and biological features of residual tumor (RT) on prognosis after neoadjuvant chemotherapy (NC) in various invasive breast cancer (IBC) subtypes

Background: The outcomes of IBC pts who received NC could be different by Subtypes Methods: From 2000 to 2018 we treated 400 II-III stage IBC patients (pts) with NC. We recorded baseline characteristics, type of NC, type of surgery, pCR (defined as the absence of invasive cells in the breast and the lymph nodes regardless of DCIS), biological features of RT. pCR and survival outcomes (in term of Disease Free Survival-DFS, Relapse Free Survival-RFS and Overall Survival-OS) also on the basis of both pre- and post- NC Ki67 levels were assessed Results: Median age was 50 yrs (r. 25-75). Population consisted of: Luminal A (LA): 3.7% Luminal B (LB): 28.25% Luminal HER2 (LHER2): 28% HER2+HR- 13.5% Triple Negative (TN):21.25% Unknown:5.3% The NC was based on tri-weekly or dose-dense (only 22 cases) anthracyclines (A) followed by weekly taxanes (T) in HER2- (249), associated with weekly carboplatin (C) in more recent cases (48) of TN and T + trastuzumab (H) ± A (40) or C (102) in HER2+ pts. All pts but 18 did received surgery: 8 for distant metastases occurrence and 10 because still on NC. Quadrantectomy was performed in 205(52%) pts. pCR was achieved in 125 (31%) pts of which 30 with non invasive residual; further 10 patients showed RT ≤1 mm pCR was reached in 41.5% in case of proliferation index by Ki67 ≥ 20% and in particular if u003e ki67 was u003e 40% regardless of Subtypes (p=0.001). All 166 HER2 + patients except 24 received H obtaining pCR in 70 (45.8%) of cases regardless chemotherapy type. pCR were 30.7% and 50% according to A- vs C-based regimen respectively. Twenty-six of 48 TN pts receiving C addition underwent S with pCR. The median Fup was 44.12 months (r: 1.35-232.6). The pCR was positively associated with DFS (HR 0.17, 95% CI 0.07-0.40), RFS (HR 0.26, 95% CI 0.13-0.50) and OS (HR 0.17, 95% CI 0.06-0.49) in overall population The association between pCR and long-term outcomes (DFS and RFS, but not OS) was greater in TN pts (EFS: HR 0.11, 95% CI 0.01-0.90; RFS: 0.12, 95% CI 0.06-0.71), in LHER2 (EFS: HR 0.20, 95% CI 0.04-0.87; RFS: 0.24, 95% CI 0.07-0.84) and in HER2+ (EFS: HR 0.11, 95% CI 0.01-0.90; RFS: 0.24, 95% CI 0.06-0.73) than in LA and LB. Postoperative low level of Ki67 ( Citation Format: Antonella Ferro, Alessia Caldara, Elisabetta Grego, Carlo Messina, Gabriella Berlanda, Paolo Cristofolini, Fabio Gasperetti, Salvatore Mussari, Carmine Fanto, Marvi Valentini, Marco Pellegrini, Mattia Barbareschi, Nicola Mirabassi, Giuseppe Carbone, Roberta Biondi, Renza Triolo, Silvia Lazzeri, Vincenzo Sabatino, Paola Bondioli, Orazio Caffo. Impact of pathologic complete response (pCR) and and biological features of residual tumor (RT) on prognosis after neoadjuvant chemotherapy (NC) in various invasive breast cancer (IBC) subtypes [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-16-24.