A Targetable EGFR-Dependent Tumor-Initiating Program in Breast Cancer

Paul Savage, Alexis Blanchet-Cohen, Timothée Revil, Dunarel Badescu, Sadiq M.I. Saleh, Yu-Chang Wang, Dongmei Zuo, Leah Liu, Nicholas R. Bertos, Valentina Munoz-Ramos, Mark Basik, Kevin Petrecca, Jamil Asselah, Sarkis Meterissian, Marie-Christine Guiot, Atilla Omeroglu, Claudia L. Kleinman, Morag Park, Jiannis Ragoussis

Therapies targeting epidermal growth factor receptor (EGFR) have variable and unpredictable responses in breast cancer. Screening triple-negative breast cancer (TNBC) patient-derived xenografts (PDXs), we identify a subset responsive to EGFR inhibition by gefitinib, which displays heterogeneous expression of wild-type EGFR. Deep single-cell RNA sequencing of 3,500 cells from an exceptional responder identified subpopulations displaying distinct biological features, where elevated EGFR expression was significantly enriched in a mesenchymal/stem-like cellular cluster. Sorted EGFR(hi) subpopulations exhibited enhanced stem-like features, including ALDH activity, sphere-forming efficiency, and tumorigenic and metastatic potential. EGFR(hi) cells gave rise to EGFR(hi) and EGFR(lo) cells in primary and metastatic tumors, demonstrating an EGFR-dependent expansion and hierarchical state transition. Similar tumorigenic EGFR(hi) subpopulations were identified in independent PDXs, where heterogeneous EGFR expression correlated with gefitinib sensitivity. This provides new understanding for an EGFR-dependent hierarchy in TNBC and for patient stratification for therapeutic intervention.