Abstract PS18-14: Elucidating the biology of high-risk ductal carcinoma in situ (DCIS) through genomics and immunohistochemical profiling of the tumor microenvironment: The DEFENSE study

Introduction: Ductal carcinoma in situ (DCIS) of the breast is a premalignant lesion representing a spectrum of biology and risk. While many patients with DCIS undergo surgical resection with no survival benefit given the indolent nature of their disease, others do possess biologically aggressive DCIS that has the potential to evolve into invasive cancer if left untreated. Yet even among those patients with biologically aggressive DCIS, their risk of dying from metastatic breast cancer is only 3.3% compared to 30-40% among patients with biologically aggressive invasive cancer.1 The DEFENSE study, supported with funding from the NCI Molecular Characterization of Screen-Detected Lesions (MCL) consortium, was designed to identify molecular, immunological, and stromal-related factors that allow DCIS to develop high-risk features without ever becoming invasive breast cancer. Methods: The overall objective of the DEFENSE study is to compare 100 patients with invasive high-risk breast cancer enrolled on the I-SPY2 trial matched based upon age and tumor molecular profile (Mammaprint) to 100 patients with high-risk DCIS, defined as having at least two of the following characteristics: large (>5cm), high-grade, hormone receptor-negative status and/or HER2-positive status. Tumors obtained from each of these patients are divided into 22 sequential sections with regions of pathologic interest identified prior to undergoing whole exome DNA sequencing, SMART-3SEQ RNA sequencing, multiplex immunofluoresence (mIF) for immune cell infiltrates, and stromal profiling by IHC. Each profiling modality is performed by a different institution included in the MCL consortium (UCSF, UCD, UCSD, Stanford, and UVM). In order to evaluate the logistic and financial feasibility of our multi-institution protocol prior to expanding to our proposed full-scale study, we are conducting a pilot study of 11 high-risk DCIS specimens. Results: The 11 pilot specimens have been successfully sent and received by each institution. HE 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS18-14.