Abstract P5-16-17: Population based long term outcomes of pathologic complete response after neoadjuvant chemotherapy in stage I-III breast cancer: The British Columbia experience

Abstract

Abstract Background: Neoadjuvant chemotherapy is a treatment option for breast cancer patients (pts) with locally advanced disease and for pts with operable breast cancer who desire breast conservation. Neoadjuvant therapy also allows for early evaluation of the effectiveness of systemic therapy. Pathologic complete response (pCR) has been shown in clinical trials to be associated with improved survival. The objective of this study was to determine if the outcomes demonstrated in clinical trials can be applied in the population based setting by comparing the outcomes of breast cancer pts who achieved pCR (no invasive disease in breast and nodes) vs. those that did not achieve a pCR. Methods: This is a retrospective cohort study of stage I-III invasive breast cancer pts treated with neoadjuvant chemotherapy from 2005 to 2010 in British Columbia. Cases were identified from the Breast Cancer Outcomes Unit database. Data was collected on demographics, tumor pathology, and type of treatment (chemotherapy, endocrine therapy, trastuzumab) and linked to standard clinical outcomes. Results: 267 pts who met inclusion criteria were identified, of whom 5% had stage I, 33% Stage II and 59% Stage III breast cancer. Median follow up was 7.4 years. Overall 74 pts (28%) demonstrated a pCR and 193 pts did not. pCR pts had better 5-yr overall survival (OS) vs. non-pCR pts: 88% vs. 73% (HR 0.43, 95% CI 0.23-0.82, p=0.01). 5-yr disease free survival (DFS) was 84% in pCR pts vs. 70% in non-pCR pts (HR 0.45, 95% CI 0.24-0.83, p=0.01). Similarly, 5-yr breast cancer specific survival (BCSS) and distant disease free survival (DDFS) were significantly better in favor of the pCR cohort: HR 0.39 (95% CI 0.18-0.82, p=0.01) and HR 0.45 (95% CI 0.24-0.83, p=0.02) respectively. pCR pts were more likely to be HER2-positive and/or ER negative. Conclusions: Our population based results showed that early stage breast cancer pts who achieved pCR after neoadjuvant chemotherapy had better outcomes on all survival parameters compared to pts who did not achieve a pCR. This finding is consistent with results from neoadjuvant clinical trials and the FDA meta-analysis. These 'real world' results demonstrate that pCR can be used as a surrogate endpoint for survival outcomes even among non-trial pts. Citation Format: Sun J, Gondara L, Diocee R, Speers C, Lohrisch C, Chia S. Population based long term outcomes of pathologic complete response after neoadjuvant chemotherapy in stage I-III breast cancer: The British Columbia experience [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P5-16-17.