Breast Cancer Research Highlights From ESMO 2026

At this year's European Society for Medical Oncology (ESMO) Congress 2026, thousands of international experts, researchers, and advocates came together to discuss the latest breakthroughs in cancer, from screening to diagnosis and treatment to survivorship.

This year's breast cancer highlights include research on new treatments for metastatic breast cancer, including early research on more effective treatments for brain mets. Researchers also shared reports on side effects from people taking giredestrant, new findings about drugs that kept people with early- and late-stage disease alive longer, and updates on two new antibody-drug conjugates.

People with hormone receptor-positive, HER2-negative metastatic breast cancer (MBC) are often first treated with a CDK4/6 inhibitor plus hormonal therapy (also called endocrine or anti-estrogen therapy). But over time the cancer may grow.

A study now suggests that combining a new CDK4 inhibitor called atirmociclib with Faslodex (chemical name: fulvestrant) may help people live longer without the cancer growing (known as progression-free survival), compared to those taking Faslodex alone or other standard therapies. Progression-free survival was about 9.5 months for people on the atirmociclib combo compared to about 6.5 months for people on Faslodex alone or other standard treatments.

Atirmociclib is different from CDK4/6 inhibitors in that it only blocks the CDK4 kinase, which is a protein that makes cancer cells grow and divide. Researchers think that it can effectively treat breast cancer and cause fewer blood-related side effects, like low white blood cell counts.

New research suggests that Dato-DXd could hold great promise as a treatment for triple-negative breast cancer (TNBC) brain metastases, which about a third of people with metastatic TNBC will develop. Early results from 61 people with brain metastases in the TROPION-Breast02 study found that Dato-DXd worked better than chemotherapy in all the areas the researchers measured. 

People getting Dato-DXd lived 7.7 months without the cancer growing, while people getting chemo lived 3.5 months. People getting Dato-DXd lived 13.5 months (with or without the cancer growing), compared to 10.7 months for people getting chemo. Additionally, about 63% of the brain metastases responded in some way to DatoDXd, compared to about 38% of brain metastases that responded to chemo. 

The researchers also looked specifically at how long people lived without the brain metastases growing — this called central nervous system progression-free survival (CNS PFS). CNS PFS ranged from 6.9 months to 19.3 months for people getting Dato-DXd; for people getting chemo, it was 1.5 to 5.8 months. This was especially interesting because it showed that Dato-DXd specifically worked in the brain.

Up to 50% of people with metastatic HER2-positive breast cancer develop brain metastases. Treating HER2-positive brain mets with a combination of Enhertu (chemical name: fam-trastuzumab-deruxtecan-nxki), also called T-DXd, and Perjeta (chemical name: pertuzumab) controlled HER2-positive brain mets better than taxane chemotherapy, Herceptin (chemical name: trastuzumab), and Perjeta — also known as THP. These are the latest results from the DESTINY-Breast09 study, which included 61 people with brain mets who received Enhertu and Perjeta or THP. After about two years, the Enhertu-Perjeta combo stopped the growth or eliminated the brain mets in 90% of the people who received it. THP stopped or eliminated the brain mets in 70% of the people who received it. The results echo findings from the DESTINY-Breast12 study and support using Enhertu for brain mets to delay or avoid whole brain radiation.

People with HER2-positive metastatic breast cancer who were first treated with a combination of anbenitamab, a new anti-HER2 medicine, and HB1801, a new form of the drug docetaxel, had longer progression-free survival than those treated with standard chemotherapy, a study has found.

After a follow-up of 21 months, about 59% of the people who received anbenitamab plus HB1801 had no signs of cancer growing compared to about 34% of people who received doctor’s choice of chemotherapy — commonly docetaxel, Herceptin (chemical name: trastuzumab), and Perjeta (chemical name: pertuzumab).

New results on patient-reported outcomes from the lidERA trial show that people taking giredestrant were less bothered by side effects than people taking tamoxifen or an aromatase inhibitor. While clinical trial results focus on the effectiveness of treatments, patient-reported outcomes include feedback from the people in the study about side effects and quality of life. Giredestrant is a hormonal therapy medicine used to reduce the risk of the cancer coming back (or recurring) after surgery for early-stage hormone receptor-positive breast cancer. 

After more than 2.5 years of follow-up, about 52% of people taking giredestrant reported not being bothered at all by side effects, compared to 47% of people taking an aromatase inhibitor or tamoxifen. About 5% of people taking giredestrant stopped taking the medicine because of side effects, compared to about 8% of people taking tamoxifen or an aromatase inhibitor. 

Trastuzumab rezetecan, an experimental antibody-drug conjugate (ADC), improved progression-free survival compared to doctor’s choice of chemotherapy in people with HER2-low metastatic breast cancer, according to a study. Progression-free survival was 16.4 months for people taking trastuzumab rezetecan versus 6.8 months for people receiving taxanes, Halaven (chemical name: eribulin), Xeloda (chemical name: capecitabine), Gemzar (chemical name: gemcitabine), or vinorelbine (brand name: Navelbine).

The improvement in progression-free survival was consistent in both hormone receptor-positive and hormone receptor-negative disease. Trastuzumab rezetecan is currently approved in China for non-small cell lung cancer and colorectal cancer and can be used in the United States for gastric cancer. 

Enhertu (chemical name: trastuzumab deruxtecan or T-DXd), another ADC, can be used to treat both HER2-low and -ultralow metastatic disease. It’s unclear if trastuzumab rezetecan is better than Enhertu, and it’s unlikely that the two medicines will be compared head-to-head. Researchers said that in countries where Enhertu is already approved, it’s likely to stay as the preferred treatment option.

The latest results from the NATALEE trial found that people with early-stage hormone receptor-positive, HER2-negative breast cancer who took Kisqali (chemical name: ribociclib) and an aromatase inhibitor lived longer than people who took an aromatase inhibitor alone. This improvement in overall survival (how long people live whether or not the cancer comes back) increased over time. After five years of follow-up, overall survival rates were 94% for people on Kisqali and an aromatase inhibitor and 93% for people on an aromatase inhibitor alone. After six years, the overall survival rates were 92% and 90%.

New findings from the postMONARCH study show that people lived longer (either with or without the cancer growing) if they got Verzenio (chemical name: abemaciclib) and Faslodex (chemical name: fulvestrant) compared to Faslodex alone for advanced-stage hormone receptor-positive breast cancer that grew during CDK4/6 inhibitor treatment. 

After three years of follow-up, overall survival was 32 months for people on Verzenio and Faslodex compared to 24.6 months for people on Faslodex alone. This difference wasn’t statistically significant, though. This means it could have been due to chance and not because of the difference in treatment. 

But the combination of Verzenio and Faslodex also improved progression-free survival (how long people lived without the cancer growing). Because of this, the researchers said the evidence favors adding Verzenio to Faslodex for cancers that grew during CDK4/6 inhibitor treatment.

Izalontamab brengitecan (iza-bren), an experimental antibody-drug conjugate, may help people with hormone receptor-positive, HER2-negative metastatic breast cancer live longer without the cancer growing than chemotherapy, according to results from the PANKU-Breast01 study.

After about 14 months of follow-up, progression-free survival was eight months for people on iza-bren and four months for people on a doctor’s choice of chemotherapy, which could have been Halaven (chemical name: eribulin), Xeloda (chemical name: capecitabine), Gemzar (chemical name: gemcitabine), or vinorelbine (brand name: Navelbine).

The ESMO Breast Cancer Annual Congress 2026, a companion conference to ESMO's annual conference that's focused just on breast cancer, took place May 6–8 in Berlin.

Can pCR show who can safely skip chemo?

Currently, many studies are looking at what doctors call de-escalating treatment. This means giving people fewer treatments or treatments that cause fewer and less severe side effects. To do this, researchers have been looking for new ways to predict who can safely skip certain treatments.

The researchers behind the PHERGain-2 trial wanted to know if people diagnosed with very treatable types of early-stage, HER2-positive breast cancer who have a pathological complete response (pCR) to treatments given before surgery can skip chemotherapy after surgery. A pCR means that no active cancer cells are present in tissue removed during surgery. It shows doctors that pre-surgery treatments were effective.

All the cancers in the study were very small, node-negative, and strongly HER2-positive, which means they would likely respond well to anti-HER2 medicines given before surgery. So these types of cancers would be more likely to have a pCR and less likely to need chemotherapy after surgery.

Early results from the study show that people with pCR who skipped chemo after surgery had better quality of life than people who received chemotherapy. But because these are early results, we don’t yet know if the rates of the cancer coming back (recurrence) are different between the treatment groups.

Using one ADC after another offers disappointing results

Results from the SATEEN trial showed that the combination of Trodelvy (chemical name: sacituzumab govitecan-hziy) and Herceptin (chemical name: trastuzumab) to treat metastatic HER2-positive breast cancer that grew during Enhertu (chemical name: fam-trastuzumab-deruxtecan-nxki) treatment wasn’t effective. Only one of the 27 cancers in the study responded to the combo treatment. Researchers had hoped the combination could be another option for people if Enhertu stops working.

It was one of the first prospective studies looking at using antibody-drug conjugates (ADCs) — Trodelvy and Enhertu — one after the other.  The two drugs target different proteins, but they both use the same type of chemotherapy, a topoisomerase 1 inhibitor. Experts think resistance to the chemotherapy part of the ADC may explain the SATEEN findings. The results also echo real-world studies that have shown limited benefits for people receiving one topoisomerase 1 inhibitor ADC after another.

 

This content is made possible by Lilly.