ESMO Breast Cancer 2026: 3 Key Takeaways

In the wake of the 2026 ESMO Breast Cancer conference, researchers and clinicians are parsing a wealth of data aimed at refining treatment precision and improving patient quality of life. Dr. Erica Mayer, director of breast cancer clinical research at the Dana-Farber Cancer Institute in Boston, identified three pivotal studies that could reshape the management of hormone receptor-positive and HER2-positive diseases.

Mayer, an associate professor of medicine at Harvard Medical School, emphasized that the current era of research is not just about finding more powerful drugs, but about identifying which patients can safely receive less intensive therapy.

Here are the noteworthy takeaways from ESMO Breast 2026:

Oral SERDs and ovarian suppression: The PREcoopERA Study

The PREcoopERA trial addressed a critical quality-of-life question for premenopausal patients with hormone receptor-positive breast cancer: Can new oral selective estrogen receptor degraders (SERDs) be used without ovarian function suppression (OFS)?

Currently, premenopausal patients receiving oral SERDs typically undergo OFS, often via monthly injections, which can cause significant side effects. The window-of-opportunity study compared the oral SERD giredestrant with and without OFS.

While all treatment arms showed high anti-proliferative activity, the study found that giredestrant monotherapy was not non-inferior to giredestrant plus OFS. Furthermore, some patients on monotherapy developed ovarian cysts, indicating elevated estradiol levels.

"If we're giving oral [SERDs] for the time being and we want to achieve optimal efficacy, we need to be giving it with ovarian function suppression," Mayer said. However, she noted that further research, including the upcoming preEMBER study, will continue to investigate if lower-risk patients might eventually be able to omit OFS.

The Limits of etDNA monitoring: The TRAK-ER Trial

Monitoring circulating tumor DNA (ctDNA) to detect minimal residual disease (MRD) is a burgeoning field, but the TRAK-ER trial results suggest clinicians must remain cautious.

In the surveillance phase of the study, 12% of survivors tested positive for ctDNA. Notably, 40% of those who tested positive were found to already have metastatic disease upon further imaging. For those who tested positive on their very first test, that number jumped to 70%.

Mayer warned that while CTDNA is a powerful prognostic tool, its clinical utility, the ability to act on the information to improve outcomes, is still unproven.

"Given the lack of data to support the actual clinical utility, we have to be very careful and hold back from using tests like that if we don't actually have a method to improve outcomes for our patients," Mayer said. She noted that learning of a high risk without having a clear treatment path can cause significant "psychological distress" for survivors.

Sparing chemotherapy in HER2-positive disease: PHERGain-2

In one of the most provocative presentations of the conference, the PHERGain-2 study explored a chemotherapy-free regimen for patients with early-stage HER2-positive breast cancer.

The trial treated patients with stage 1, HER2 3+ tumors using only the antibodies Herceptin (trastuzumab) and Perjeta (pertuzumab) (HP), omitting traditional toxic chemotherapy. The results were striking: 60% of patients achieved a pathologic complete response (pCR), meaning their cancer had completely disappeared at the time of surgery.

"It is very provocative to consider if we could treat these patients with a chemotherapy-free regimen and achieve excellent outcomes, improved quality of life and spare exposure to the toxicities of chemotherapy," Mayer said.

While Mayer noted this approach is "not ready for prime time" until longer-term follow-up data is available, she highlighted it as a major step toward de-escalating treatment for favorable-prognosis patients.

A message of progress and compassion

Beyond the data, Mayer emphasized that the overarching goal of breast oncology remains twofold: curing the disease while protecting the person.

"We continue to make dramatic progress in identifying new targets ... and demonstrating through clinical trials how well the new therapies work in comparison to treatments we used in years past," Mayer said.

She encouraged patients to feel empowered by the ongoing research into the patient experience. "It is very important as we develop new drugs to simultaneously be considering what the impact of these drugs are on our patients and making sure that people can take the highly effective therapies and get the best response and also feel as good as possible," she said

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