ENDORSE: a prognostic model for endocrine therapy response in advanced estrogen-receptor positive breast cancers

Endocrine therapy remains the primary treatment for advanced and metastatic estrogen receptor-positive (ER+) breast cancers. Patients who progress on endocrine therapy may benefit from add-on treatment targeting the PI3K/MTOR signaling pathways or by switching to chemotherapy. However, these options are only available after progression on first-line treatment with endocrine therapy. In the absence of reliable prognostic tests for advanced ER+ breast cancers, it is currently not possible to stratify patients into pertinent treatment arms at the baseline. To address this, we have developed a low-dimensional endocrine response signature (ENDORSE) model for advanced ER+ breast cancers. The ENDORSE model was developed using the baseline tumor transcriptomes and long-term survival outcomes of >800 invasive ER+ breast cancers and predicts the risk of death on endocrine therapy. ENDORSE was validated in multiple clinical trial datasets for endocrine therapy response in metastatic ER+ breast cancers and demonstrated superior predictive performance over clinical factors and published gene signatures. Our results show that ENDORSE is a reproducible and accurate prognostic model for endocrine therapy response in advanced and metastatic ER+ breast cancers.