SUMMARY ? PROJECT 4 Women with substantial residual disease after neoadjuvant chemotherapy (NAC) have poor prognosis with substantial risk of early recurrence. Conversely, women who achieve pathologic complete response or `pCR' (complete eradication of tumor) prior to surgery have very good outcomes. The I-SPY2 clinical trial is an innovative multicenter, multi-agent clinical platform trial that uses an adaptive randomized study design to accelerate the development of new agents and paired biomarkers of response in women with locally advanced breast cancer. To date, 10 novel agents have begun evaluation, and 3 have `graduated' having a high (>85%) probability of success in a phase III trial; over 1000 patients have enrolled, with 250 more each year. Despite these advances, may women still fail to reach pCR. Driven by advances in MRI imaging assesments, this Program Project aims to improve pCR rates by modifying I-SPY 2 to include non-invasive identification of patients with insufficient response to NAC, then redirecting their treatment to another, biologically targeted therapy selected based upon the presence of biomarkers of response present in their tumor. In this project, we will use the substantial archived specimens and data sets from I-SPY 2 to identify new biomarkers and develop the framework for evidence-based selection of substitute treatments. Our hypothesis is that tumor characteristics at time of presentation will assist in the identification drug strategies that will successfully convert a ?non-responder? into a patient with a pCR. To achieve our goals of identifying successful drug regimens that can be used to redirect patient's therapies, we will follow a research plan consisting of three specific aims: 1) utilize the I-SPY2 qualifying biomarker evaluation (QBE) framework to identify biomarkers of drug response based upon tumor immune microenvironment analyses, and assign probability scores to each drug-biomarker pair; 2) expand the I-SPY2 predicted drug sensitivity portfolio to single agents or combination therapies not yet within the I-SPY 2 drug portfolio, based on gene expression profiles of responders/non- responders and drug-gene expression databases from breast and other cancer cell lines; and 3) create an integrated drug response prediction matrix from all sources, and establish quantitative and qualitative strategies for the rational, evidence-based selection of agents for reassignment.. We will work closely with the Project 1 clinical team to refine our models in a way that maintains clinical context. We anticipate a unique and important synergy to emerge through collaborations with Project 3, the goal of which is to characterize the dynamics of molecular pathways of resistance under therapeutic pressure. This project will also leverage the broad experience of the investigators and the bioinformatics expertise within the shared cores. The clinical goals of the overall program project are a significant motivating factor for this study, which will result in the development of important new information resources that will find utility within the I-SPY 2+ TRIAL and beyond.