Abstract P4-09-05: Expression of breast cancer stem cell marker as a predictor of prognosis and response to trastuzumab in HER2-positive breast cancer

Abstract BACKGROUND: Breast cancer stem cells (BCSCs) have been suggested to have clinical implications for cancer therapeutics because of its proposed role in chemoresistance. The aim of this study was to investigate the impact of BCSC marker expression in clinical outcome and trastuzumab response HER2-postive breast cancer. METHODS: We analyzed the clinical significance of BCSC marker (ALDH1 and CD44+/CD24-) expression in 242 HER2-positive primary breast cancers using immunohistochemistry. In addition, we examined the relationship between BCSC marker expression, trastuzumab response and clinical outcome in 447 primary, and 112 metastatic HER2-positive breast cancer patients treated by trastuzumab. RESULTS: In the first set, ALDH1 positivity and CD44+/CD24- phenotype were detected in 10.0% and 29.9%, respectively. ALDH1 positivity and CD44+/CD24- phenotype correlated with hormone receptor negativity. In survival analyses, CD44+/CD24- phenotype, but not ALDH-1 expression, was found to be an independent prognostic factor for poor disease-free and overall survival of patients in entire group, and in subgroup not receiving trastuzumab. In HER2-positive primary breast cancer patients treated by adjuvant trastuzumab, CD44+/CD24- phenotype was also an independent poor prognostic factor for disease-free survival. However, ALDH1 positivity and CD44+/CD24- phenotype had no effect on trastuzumab response and survival in patients with metastatic HER2 positive breast cancer. CONCLUSION: These results suggest that CD44+/CD24- phenotype can be used as a prognostic factor for clinical outcome and a predictive factor of trastuzumab response in patients with HER2-positive primary breast cancer. Citation Format: Seo AN, Lee HJ, Kim EJ, Jang MH, Kim YJ, Kim JH, Kim S-W, Ryu HS, Park IA, Im S-A, Gong G, Jung KH, Park SY. Expression of breast cancer stem cell marker as a predictor of prognosis and response to trastuzumab in HER2-positive breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-09-05.