Researchers presented the latest clinical trials in breast cancer treatment at the 2026 Congress of the European Society for Medical Oncology (ESMO). The key findings concern metastatic tumors, brain metastases, and the efficacy of next-generation drugs.
New CDK4 inhibitor slows tumor growth
In patients with hormone receptor-positive (HR+), HER2-negative metastatic breast cancer, the combination of the next-generation CDK4 inhibitor atirmociclib and fulvestrant (Faslodex) increased progression-free survival to 9.5 months, compared with 6.5 months with standard treatment.
Unlike traditional CDK4/6 inhibitors, atirmociclib selectively blocks the CDK4 protein, halting the division of cancer cells while reducing blood-related side effects, such as a decrease in white blood cell counts.
Dato-DXd outperforms chemotherapy in patients with brain metastases
In approximately one-third of cases of triple-negative breast cancer (TNBC), the disease spreads to the brain. The TROPION-Breast02 study showed that Dato-DXd outperformed standard chemotherapy across all reported measures in 61 patients with brain metastases:
- Progression-free survival was 7.7 months in the Dato-DXd group, compared with 3.5 months in the chemotherapy group.
- Overall survival increased from 10.7 to 13.5 months.
- Brain metastases responded to treatment in 63% of patients receiving Dato-DXd, compared with 38% of those receiving chemotherapy.
- The period without progression in the central nervous system was extended to 6.9–19.3 months, compared with 1.5–5.8 months with chemotherapy.
New combination controls HER2-positive metastatic tumors
A combination of the novel anti-HER2 drug anbenitamab and a new formulation of docetaxel (HB1801) demonstrated better results than standard chemotherapy. After 21 months of follow-up, 59% of patients receiving the combination had no signs of tumor growth, compared with 34% of those receiving the standard regimen of docetaxel, trastuzumab, and pertuzumab.
Giredestrant is better tolerated than tamoxifen
The lidERA trial evaluated adjuvant treatment for early-stage hormone receptor-positive breast cancer following surgery. After 2.5 years of follow-up, 52% of patients reported no bothersome side effects with giredestrant, compared with 47% in the tamoxifen and aromatase inhibitor groups. Only 5% of patients discontinued giredestrant because of side effects, compared with 8% receiving standard hormone therapy.
New antibody-drug conjugates (ADCs) against metastatic cancer
- Trastuzumab rezetecan: In metastatic breast cancer with low HER2 expression, the drug increased progression-free survival to 16.4 months, compared with just 6.8 months with standard chemotherapy.
- Iza-bren (izalontamab brengitecan): According to the PANKU-Breast01 study, this experimental drug doubled progression-free survival in hormone receptor-positive, HER2-negative metastatic breast cancer, achieving 8 months compared with 4 months with chemotherapy.
Kisqali and Verzenio improve survival outcomes
- Kisqali (ribociclib): Six-year data from the NATALEE trial confirmed that combining Kisqali with an aromatase inhibitor in early-stage HR-positive, HER2-negative breast cancer increased overall survival to 92%, compared with 90% with an aromatase inhibitor alone.
- Verzenio (abemaciclib): According to the postMONARCH trial, in advanced HR-positive breast cancer that continued to progress despite treatment with CDK4/6 inhibitors, the combination of Verzenio and fulvestrant increased overall survival to 32 months, compared with 24.6 months with fulvestrant alone. Although the difference in overall survival did not reach statistical significance, the combination clearly delayed disease progression.
Key takeaways from ESMO Breast 2026: Avoiding chemotherapy and overcoming resistance
- Treatment de-escalation (PHERGain-2): Patients with small, early-stage HER2-positive tumors whose cancer cells were completely eliminated by neoadjuvant targeted therapy (a pathological complete response, or pCR) avoided postoperative chemotherapy and maintained a substantially better quality of life. Researchers are continuing to monitor long-term recurrence risks.
- Failure of sequential treatment with two ADCs (SATEEN): In patients whose HER2-positive metastatic tumors progressed during treatment with Enhertu, the combination of Trodelvy and trastuzumab (Herceptin) was ineffective: only one of 27 tumors responded to treatment. Since both Enhertu and Trodelvy use the same type of chemotherapy payload, a topoisomerase I inhibitor, researchers attribute the lack of efficacy to resistance to this component.
