Abstract 1684: Multi-omics profiling of breast cancers during neoadjuvant chemotherapy identified distinct molecular changes and biomarkers associated with clinical response

Abstract

Abstract The molecular bases underlying neoadjuvant chemotherapy (NAC) response are poorly understood. To elucidate the effects of NAC on breast tumor biology and its association with clinical outcome, we have conducted WES and RNA-Seq profiling of a longitudinal breast cancer (BC) cohort consisting of 146 cases (281 tumors, 109 pairs), including 55 (38%) that achieved pathologic complete responses (pCR) and 91 (62%) that harbored residual diseases at time of surgery. Tumor biopsies were collected for each patient at three time points - pre-treatment, three weeks after the first cycle of anthracycline and cyclophosphamide (AC) and at the time of surgery, after 3 more cycles of AC followed by 4 cycles of taxane. In addition to somatic mutations and copy number alterations, we also derived a comprehensive set of genomic and molecular features for each tumor including chromosomal instability, loss-of-heterozygosity, mutation burden, mutation signatures and expression signatures for oncogenic signaling pathways and immune cell subsets. Virtual microdissection analysis inferred 14 factors that represent distinct tissue compartment including a tumor infiltrating lymphocyte (TIL) factor and revealed that initial NAC treatment increased stromal and adjacent normal tissue fractions while reducing tumor cellularity. NAC also induced dynamic changes in immune gene expressions over time, a pattern that was validated through detecting and quantifying the density of TILs from H&E images. To investigate NAC induced changes in tumor intrinsic biology we classified tumors into five oncogenic cellular states on a reference Onco-GPS map defined by transcriptional signatures from breast cancer cell lines. We observed that, as a result of NAC treatment, tumors often change from one oncogenic state to another, transiently upregulating an EMT program that appears to mediate drug resistance and increase the likelihood of residual disease. Multiple regression and multivariate analyses were performed to identify predictive biomarkers of pCR status while adjusting for BC subtypes and tumor purity. We found that ER+ subtype and estrogen response signature but not Ki-67 were independently associated with NAC response. Within TNBC, the immunomodulatory subtype was enriched in responders while the basal-like subtype had the poorest response. Pretreatment TIL and changes in TIL level over time were independently associated with NAC response, implicating anti-tumor immunity in mediating the efficacy of chemotherapies. Through multi-omics characterization of longitudinally paired tumor biopsies, we have revealed dynamic changes in the tumor molecular states in BC patients undergoing NAC treatment, identified molecular markers of treatment outcome and derived insights into the mechanism of action as well as resistance to an important class of therapy. Citation Format: Samir Lal, Ying Ding, Jeong Eon Lee, Soo-Hyeon Lee, Se Kyung Lee, Jae-Yong Nam, Jong Han Yu, Yoon-la Choi, Seok Won Kim, Seok Jin Nam, Ji-Yeon Kim, Sripad Ram, Eric Powell, Keith A. Ching, Pablo Tamayo, William Kim, Huwate Yeerna, Soo Youn Cho, Vinicius Bonato, Shibing Deng, Jinho Kim, Hyuntae Shin, Woong-Yang Park, Paul A. Rejto, Jadwiga Bienkowska, Yeon-Hee Park, Zhengyan Kan. Multi-omics profiling of breast cancers during neoadjuvant chemotherapy identified distinct molecular changes and biomarkers associated with clinical response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1684.