Abstract A062: Somatic engineering of rat models to recapitulate human breast cancer evolution and heterogeneity

Abstract

Abstract Estrogen receptor (ER) positive breast cancer accounts for over 75% of all presenting clinical cases. In addition, almost all Ductal Carcinoma in situ (DCIS) lesions, now accounting for about 25% of all newly diagnosed ‘breast cancers’, are ER-dependent. Despite the high occurrence, the molecular underpinnings regulating DCIS initiation and progression to invasive disease remain elusive. This gap in knowledge is primarily due to the dearth of suitable preclinical models that accurately emulate breast cancer heterogeneity. To overcome this impediment, we developed a platform of somatic models by engineering the rat mammary gland and manipulating the genes most frequently mutated in hormone-dependent (pre-)breast cancer. This has successfully led to the generation of ER-positive disease models that provide a nuanced understanding of ER functionality and the complex mechanisms of ER signaling, which we show to be dependent on the cancer genotype. This has potential implications for the formulation of innovative endocrine therapy treatment regimens. Our models have generated an array of tumor types, including ductal and lobular carcinomas, manifesting both in situ and invasive phenotypes, faithfully recapitulating human breast disease and the evolution of tumorigenesis. Intriguingly, our results indicate how different oncogenic mutations modulate not only the architectural and histopathological characteristics of cancer but also the immune microenvironment, thereby generating possibilities for future therapeutic testing. Our research augments the range of available ER-positive in situ and invasive breast cancer models, benefitting the stratification of indolent from aggressive disease and facilitating the exploration of novel treatment strategies for this pervasive breast cancer subtype. Citation Format: Catrin Lutz, Ji-Ying Song, Hendrik A Messal, Madelon Badoux, Timo Eijkman, Bim de Klein, Jelle Wesseling, Jos Jonkers. Somatic engineering of rat models to recapitulate human breast cancer evolution and heterogeneity [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr A062.