ESR1 mutation

P1/2, N=49, Completed, Carrick Therapeutics Limited | Active, not recruiting --> Completed

P3, N=510, Recruiting, Olema Pharmaceuticals, Inc. | N=370 --> 510

Furthermore, early ctDNA clearance identifies responding patients, and the combination of low ER activity and high ctDNA burden predicts rapid clinical progression. These findings provide a framework for personalizing future breast cancer therapies by integrating liquid biopsies with tissue-based signatures.

P3, N=240, Recruiting, MedSIR | Active, not recruiting --> Recruiting

In concordance, validation on ESR1mut patient tumors shows decreased IL-17a and IL-1β. Collectively, our findings reveal that ESR1 mutations contribute to an immunosuppressive tumor microenvironment by dampening cytokine secretion and immune cell activity.

Our findings suggest a unique genomic and immunologic landscape in MaBC requiring a sex-informed approach and provide candidate therapeutic targets and mechanisms of resistance.

Key 2025 findings (50 clinical trials) include: (1) confirmation of overall survival benefit with adjuvant CDK4/6 inhibitors in HR+/HER2- early breast cancer (monarchE: HR = 0.842, p = 0.0273); (2) establishment of trastuzumab deruxtecan (T-DXd) as a new standard in high-risk HER2+ early disease (DESTINY-Breast05: IDFS HR = 0.47) and first-line metastatic settings (DESTINY-Breast09: PFS HR = 0.58); (3) validation of TROP2-directed ADCs as first-line therapy for metastatic triple-negative breast cancer (ASCENT-03: PFS HR = 0.62; BEGONIA: ORR 79%); (4) paradigm shift to proactive, liquid biopsy-guided therapy switching (SERENA-6: PFS HR = 0.44); (5) updated efficacy and safety of the oral SERD imlunestrant from the EMBER-3 trial, supporting its role in ESR1-mutated advanced breast cancer and in combination with abemaciclib; (6) confirmation of long-term survival benefit for neoadjuvant carboplatin in early TNBC and new positive adjuvant data; (7) pivotal advances in HER2+ metastatic disease sequencing with tucatinib and T-DXd; (8) evidence supporting optimized adjuvant endocrine therapy in HER2+/HR+ early disease; and (9) emergence of novel agents with improved therapeutic indices, including PROTAC degraders, oral SERDs, and mutant-selective PI3K inhibitors. Unifying themes include biomarker-driven personalization, strategic treatment sequencing, management of unique toxicities, and emphasis on patient-reported outcomes. Future challenges include optimizing treatment integration, managing financial toxicity, and ensuring equitable global access.

P1, N=96, Recruiting, Boundless Bio, Inc. | Not yet recruiting --> Recruiting

P1, N=96, Not yet recruiting, Boundless Bio

By integrating data from clinical trials, molecular analyses, and patent landscapes, this review illustrates how multimechanistic, biomarker-guided therapies supported by advanced drug-delivery technologies are redefining contemporary precision oncology in breast cancer. The emerging therapeutic paradigm underscores the convergence of targeted therapy, immunomodulation, synthetic lethality, and localized immune-activating approaches, charting a path toward further personalization of treatment in the years ahead.

P1/2, N=99, Recruiting, Forward Pharmaceuticals Co., Ltd. | Phase classification: P1 --> P1/2 | Trial completion date: Feb 2026 --> Mar 2028 | Trial primary completion date: Nov 2025 --> Mar 2026