Caris Life Sciences' Real-World Data Uncovers Metastatic Breast Cancer Patient Responses and Resistance to Trastuzumab Deruxtecan

IRVING, Texas, Jan. 28, 2026 /PRNewswire/ -- Caris Life Sciences® (NASDAQ:CAI), a leading, patient-centric, next-generation AI TechBio company and precision medicine pioneer, has published a study in Nature's npj Breast Cancer journal titled, "Mechanisms of Resistance to Trastuzumab Deruxtecan in Breast Cancer Elucidated by Multiomic Molecular Profiling." Utilizing large-scale real-world clinico-genomic data and Caris's comprehensive multiomic profiling, Caris scientists uncovered clinically relevant mechanisms of resistance to trastuzumab deruxtecan (T-DXd) in metastatic breast cancer. This study explains why patient responses vary and reveals how resistance can evolve over time.

This study addresses a critical gap in understanding why responses to T–DXd, an antibody–drug conjugate approved by the FDA for HER2-positive and HER2-low metastatic breast cancer, vary widely since resistance to T–DXd is common. By combining large-scale, real-world clinical outcomes with Caris's comprehensive molecular profiling, including whole exome sequencing (WES) and whole transcriptome sequencing (WTS), the study enables a population-level analysis of resistance pathways across DNA, RNA and protein expression.

"In this large real-world analysis, clinical outcomes allowed Caris to pinpoint molecular features linked to treatment-specific survival," said George W. Sledge, Jr., MD, Caris EVP and Chief Medical Officer. "Post–treatment molecular shifts further reveal biologically plausible routes to acquired resistance, underscoring that RNA–level and multiomic profiling can provide actionable insights beyond standard HER2 classification to better stratify patients and inform therapies." 

The study analyzed 2,799 T–DXd–treated breast cancer patients and found that WTS identified ERBB2 (HER2) and ABCC1 as the strongest transcriptomic predictors of T–DXd–specific overall survival. Higher ERBB2 expression correlated with improved outcomes, while higher ABCC1 correlated with poorer outcomes, independent of HER2 category.

ABCC1 further stratified outcomes within HER2–defined subgroups, indicating predictive value beyond standard HER2 testing and post–treatment samples showed increased ABCC1 expression alongside enrichment of mutations in ERBB2, NFE2L2, KEAP1 and TOP1. Consistent with acquired resistance mechanisms. Preclinical models supported a functional, context–dependent role for ABCC1–mediated drug efflux in T–DXd resistance.

"This study demonstrates how population–scale, multiomic real–world data can drive high impact translational discoveries, reinforcing the value proposition for patients and equipping biopharma with actionable insights into resistance biology to guide next–generation drug development," said David Spetzler, MS, PhD, MBA, Caris President.

About Caris Life Sciences

Caris Life Sciences® (Caris) is a leading, patient-centric, next-generation AI TechBio company and precision medicine pioneer that is actively developing and commercializing innovative solutions to transform healthcare. Through comprehensive molecular profiling (Whole Exome and Whole Transcriptome Sequencing) and the application of advanced AI and machine learning algorithms at scale, Caris has created the large-scale, multimodal clinico-genomic database and computing capability needed to analyze and further unravel the molecular complexity of disease. This convergence of next-generation sequencing, AI and machine learning technologies, and high-performance computing provides a differentiated platform to develop the latest generation of advanced precision medicine diagnostic solutions for early detection, diagnosis, monitoring, therapy selection and drug development. 

Caris was founded with a vision to realize the potential of precision medicine in order to improve the human condition. Headquartered in Irving, Texas, Caris has offices in Phoenix, New York, Cambridge (MA), Tokyo, Japan and Basel, Switzerland. Caris or its distributor partners provide services in the U.S. and other international markets. 

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