Transcriptomic Profiling of Mouse Mammary Tumors Enables Prognostic and Predictive Biomarker Discovery for Human Breast Cancer

The development and validation of prognostic and predictive biomarkers in breast cancer is limited by the availability of well-annotated datasets linking tumor molecular features to treatment response and survival outcomes. To address this need, we generated an extensive mouse models dataset comprised of 26 immunocompetent mammary tumor models spanning diverse genetic backgrounds, epithelial-mesenchymal states, the basal-luminal axis, and distinct immune microenvironments. For each model, survival was measured under no treatment, immune checkpoint inhibition (ICI), and carboplatin/paclitaxel chemotherapy, and RNA-sequencing was performed on baseline tumors and on 7-day on-treatment samples for both regimens. Baseline murine tumor gene expression features were used to train a machine learning Elastic Net model that predicted survival outcomes on multiple human breast cancer datasets with performance comparable to that of existing prognostic assays. Models trained for ICI benefit, using either the untreated or 7-day ICI treated samples, predicted ICI benefit on human ICI treated datasets, with the 7-day treated tumor model showing better performance. A predictor of carboplatin/paclitaxel response developed from the murine mammary tumor data performed well in mice but did not generalize to human chemotherapy cohorts. Finally, comparison of multiple computational approaches, including XGBoost, random forests, and support vector regression, showed that all methods successfully predicted survival outcomes, with Elastic Net offering the best performance and interpretability. These results indicate conserved cancer biology between mouse and human tumors for prognosis and ICI response and establish a large preclinical dataset with linked phenotypic and genomic data as a resource for biomarker discovery.