ASCO 2026: BREAST CANCER RESEARCH SUMMARY

Highlights from the 2026 ASCO Annual Meeting

The American Society of Clinical Oncology (ASCO) Annual Meeting is one of the most important events in the global cancer calendar, where researchers and clinicians gather to share the latest advances in cancer care. This year’s conference, held in Chicago, featured exciting developments in breast cancer research — many of which are expected to change treatment options and improve outcomes for women diagnosed with the disease.

Here are some of the key highlights from ASCO 2026, summarised for our community.

OPTIMA

The OPTIMA clinical trial has found that many people with breast cancer can safely avoid chemotherapy with the use of a tumour gene test, potentially sparing them unnecessary side effects without increasing the risk of the cancer returning.

OPTIMA was designed to safely reduce the use of unnecessary chemotherapy for people with newly diagnosed breast cancer. It followed more than 4,400 patients worldwide and Breast Cancer Trials coordinated the trial in Australia and New Zealand, where 263 patients participated in the study.

The findings indicate that people aged 40 and over, whose tumours have a low Prosigna test score, can be treated safely with hormone blocking therapy alone, potentially transforming care for thousands of patients each year. Of the 4,429 people who took part in the trial, more than two-thirds (68%) had a low Prosigna score. For this group, the results showed that outcomes were very similar whether chemotherapy was given or not. Five years after treatment:

• 91.5% of those who received standard chemotherapy alongside hormone blocking therapy were alive and free from breast cancer recurrence
• 90.4% of those who received treatment based on the Prosigna test were also alive and recurrence-free, with 2/3 able to avoid chemotherapy

A statistical test showed that at the most, only 2% of patients with a low Prosigna score treated with chemotherapy will benefit from this treatment. This means that many patients will safely be able to be spared unnecessary side effects of chemotherapy.

CAPTURE

The CAPTURE clinical trial has concluded that one of the current standard of care options – chemotherapy with capecitabine – in metastatic breast cancer patients whose cancer has progressed on prior hormone blocking therapy, continues to be an effective treatment.

The study aimed to discover if women and men with hormone-receptor positive metastatic breast cancer may have benefited from a novel combination of drugs designed to improve progression free survival and offer a new treatment option.

While it was hoped that this new treatment would result in better breast cancer control for these patients, the trial showed that the outcomes were not superior to the current standard of care, which we know is an effective, well-tolerated option.

CAPTURE was coordinated by Breast Cancer Trials in Australia and New Zealand, involved 58 participants at 22 sites and was open to both men and women.

LidERA

The lidERA study tested a new hormone therapy drug called giredestrant in people with early-stage hormone receptor-positive (ER-positive), HER2-negative breast cancer, the most common type of breast cancer. After surgery and any necessary chemotherapy, patients usually take hormone-blocking medicines for several years to reduce the risk of the cancer returning. Researchers wanted to know whether giredestrant could do a better job than today’s standard hormone treatments.

More than 4,100 patients from around the world took part in the trial. Participants were randomly assigned to receive either giredestrant or standard hormone therapy, such as an aromatase inhibitor or tamoxifen.

The results were very encouraging. Patients taking giredestrant had a 30% lower relative risk of invasive breast cancer returning or death compared with those receiving standard hormone therapy. The benefit was seen across a range of patient groups, including both premenopausal and postmenopausal women.

Importantly, giredestrant was generally well tolerated. Side effects were similar to those seen with standard hormone therapies, and fewer patients stopped treatment because of side effects compared with the standard treatment group.

In simple terms, lidERA is the first large study in more than two decades to show that a new type of hormone therapy can outperform current standard treatments in early-stage ER-positive breast cancer. If approved, giredestrant could become a new option to help reduce the risk of breast cancer returning after initial treatment.

GPL-1 Drugs and Breast Cancer Recurrence

Several observational studies presented at ASCO 2026 suggested a possible link between GLP-1 medicines and better breast cancer outcomes, generating considerable interest among researchers.

The studies focused on GLP-1 receptor agonists such as semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro), medicines commonly used to treat diabetes and obesity. Researchers analysed large real-world databases to explore whether people taking these drugs experienced different cancer outcomes compared with similar patients not taking them.

One study involving more than 100,000 women found that those taking GLP-1 medicines were about 30% less likely to be diagnosed with breast cancer. Other analyses suggested that people with breast cancer and several other obesity-related cancers who were taking GLP-1 drugs were less likely to progress to advanced or metastatic disease. In breast cancer specifically, one analysis reported about a 43% lower risk of progression to stage 4 disease compared with a matched control group.

Researchers believe the benefits may be related to weight loss, reduced inflammation, improved insulin regulation, or possibly direct effects on cancer-related pathways. However, the studies were observational and cannot prove that the drugs themselves caused the improved outcomes.

In simple terms, the ASCO 2026 findings suggest that GLP-1 medicines may do more than help people lose weight—they could potentially reduce the risk of breast cancer developing, recurring, or spreading. However, definitive proof will require prospective clinical trials, several of which are now being planned.

This was one of the most talked-about “emerging stories” at ASCO 2026 because it raises the possibility that drugs already used by millions of people could eventually become part of strategies to improve breast cancer outcomes. However we are not yet at the stage where doctors would prescribe GLP-1 drugs specifically to prevent breast cancer recurrence.

SENOMAC

The SENOMAC study examined whether many women with early breast cancer can safely avoid a more extensive operation in the underarm area after cancer is found in one or two sentinel lymph nodes. Traditionally, finding cancer in these lymph nodes led to an axillary lymph node dissection (ALND), a procedure that removes many additional lymph nodes but can cause long-term side effects such as arm swelling (lymphoedema), pain, numbness and reduced arm movement.

The study included more than 2,500 patients from five European countries, making it the largest trial of its kind. Researchers compared patients who underwent the standard ALND with those who did not have further lymph node surgery after a positive sentinel node biopsy.

The results were very reassuring. After five years of follow-up, survival rates were virtually identical between the two groups. Overall survival was 94.4% in patients who avoided ALND and 93.4% in those who underwent the procedure, showing that skipping the extra surgery did not compromise cancer outcomes.

Importantly, patients who avoided ALND experienced significantly fewer long-term arm problems and better arm function. Severe arm-related disability was much less common, and patients reported better quality of life related to arm symptoms.

In simple terms, SENOMAC showed that many patients with limited cancer spread to the underarm lymph nodes can safely avoid extensive lymph node surgery without affecting their chances of survival. This means fewer long-term side effects and a better quality of life, while maintaining excellent cancer control.

AXSANA

The AXSANA study looked at whether women with breast cancer who have cancer in their underarm (axillary) lymph nodes before treatment can safely avoid extensive lymph node surgery after receiving chemotherapy before surgery. Traditionally, many of these patients undergo an axillary lymph node dissection, which removes many lymph nodes but can cause long-term side effects such as arm swelling (lymphoedema), pain and reduced shoulder movement.

AXSANA followed more than 3,000 patients across Europe who received chemotherapy before surgery. Researchers evaluated different approaches to assessing the lymph nodes afterwards, including less invasive procedures such as targeted axillary dissection, where only the lymph nodes known to have contained cancer and a small number of key “sentinel” nodes are removed.

The results showed that less extensive surgery was increasingly being used in patients whose lymph nodes appeared cancer-free after treatment, with very low rates of cancer returning in the underarm area during follow-up. The findings provide reassurance that many patients can safely avoid full lymph node dissection when they respond well to treatment before surgery.

Importantly, reducing the extent of surgery can help lower the risk of complications, particularly lymphoedema, which can significantly affect quality of life long after cancer treatment has finished.

In simple terms, AXSANA supports a growing shift toward less invasive surgery for the underarm in selected breast cancer patients. By tailoring surgery to how well the cancer responds to treatment, doctors may be able to achieve the same cancer control while reducing long-term side effects and improving quality of life.

NCT01019616

The NCT01019616 study focused on people with hormone receptor-positive (HR-positive), HER2-negative breast cancer who still had cancer remaining in the breast or lymph nodes after receiving chemotherapy before surgery. These patients are known to have a higher risk of the cancer returning, and doctors have long debated whether giving additional chemotherapy after surgery can improve outcomes.

The study enrolled 400 women in China with lymph node-positive breast cancer. After surgery, patients were randomly assigned to receive either standard hormone therapy alone or additional chemotherapy followed by hormone therapy. The chemotherapy used was deliberately different from the drugs patients had already received before surgery, in an attempt to overcome treatment resistance.

The updated results presented at ASCO 2026 showed that adding this “non-cross-resistant” chemotherapy led to improved long-term survival outcomes compared with hormone therapy alone. The benefits were seen in reducing the risk of cancer returning and translated into improved overall survival with extended follow-up.

In simple terms, this study suggests that for some patients whose breast cancer does not respond well to initial chemotherapy, switching to a different type of chemotherapy after surgery may provide an additional chance to reduce the risk of recurrence and improve survival. The findings support a more personalised approach, where treatment decisions are guided by how the cancer responds to earlier therapy rather than using the same strategy for everyone.

One caveat is that this was a study conducted in a specific patient population before many of today’s newer targeted treatments became widely available, so doctors will consider these results alongside modern treatment options.

SAKK REDUSE

The SAKK REDUSE study looked at whether people with breast cancer that has spread to the bones could receive denosumab (a drug that helps strengthen bones and reduce complications) less often without losing its benefits. Traditionally, denosumab is given every four weeks, but researchers wanted to know if giving it every 12 weeks after an initial treatment period would work just as well.

The study enrolled 1,380 patients with either metastatic breast cancer or advanced prostate cancer involving the bones. Participants were randomly assigned to continue the standard four-week schedule or switch to a 12-week schedule after an initial loading phase. Researchers then tracked serious bone-related complications such as fractures, spinal cord compression, or the need for surgery or radiation to the bones.

The results were very reassuring. Patients receiving denosumab every 12 weeks had almost exactly the same protection against bone complications as those receiving treatment every four weeks. The study met its main goal, showing that the less frequent schedule was not inferior to the standard approach.

Importantly, patients on the 12-week schedule experienced fewer side effects, including lower rates of low calcium levels and osteonecrosis of the jaw, a potentially serious dental complication. They also required fewer clinic visits and treatments.

In simple terms, SAKK REDUSE showed that many patients with breast cancer that has spread to the bones can receive denosumab every three months instead of every month without compromising effectiveness, while reducing side effects, treatment burden and healthcare costs. The investigators concluded that the 12-week schedule should become a new standard of care for these patients.

ASCENT-03

The ASCENT-03 study evaluated whether sacituzumab govitecan (Trodelvy), a targeted cancer treatment known as an antibody-drug conjugate, could work better than standard chemotherapy as the first treatment for people with advanced triple-negative breast cancer (TNBC) who were not suitable candidates for immunotherapy. This is an important group of patients because treatment options are often limited and outcomes can be poor.

More than 550 patients from around the world took part in the study. Participants were randomly assigned to receive either sacituzumab govitecan or standard chemotherapy. The goal was to see which treatment could keep the cancer under control for longer.

The results were very encouraging. Patients treated with sacituzumab govitecan experienced a 38% reduction in the risk of their cancer worsening or death compared with those receiving chemotherapy. The study met its primary goal and showed a clear improvement in the length of time patients lived without their cancer progressing. Researchers also reported longer-lasting responses to treatment, with no unexpected safety concerns.

Additional analyses presented at ASCO 2026 showed that the benefits of sacituzumab govitecan were seen across a range of patient groups, regardless of tumour biomarkers such as Trop-2 expression, BRCA status or HER2-low status.

In simple terms, ASCENT-03 suggests that sacituzumab govitecan could become a new first-line treatment option for people with advanced triple-negative breast cancer who cannot receive immunotherapy, helping keep their cancer under control for longer than standard chemotherapy.

TROPION Breast-02

The TROPION-Breast02 study looked at a new targeted treatment called datopotamab deruxtecan (Dato-DXd) for people with advanced triple-negative breast cancer (TNBC), one of the most aggressive forms of breast cancer. The study focused on patients for whom immunotherapy was not considered a suitable option, leaving chemotherapy as the usual standard treatment.

Researchers compared Dato-DXd with standard chemotherapy in more than 600 patients who had not previously received treatment for their metastatic disease. Dato-DXd is an antibody-drug conjugate, meaning it is designed to deliver chemotherapy directly to cancer cells while limiting exposure to healthy cells.

The results were highly encouraging. Patients receiving Dato-DXd went a median of 10.8 months before their cancer worsened, compared with 5.6 months for those receiving standard chemotherapy. They also lived longer overall, with a median survival of 23.7 months versus 18.7 months. The treatment reduced the risk of cancer progression by 43% and the risk of death by 21% during the study period.

Importantly, patients receiving Dato-DXd reported maintaining their quality of life for longer, and side effects were generally manageable and consistent with previous studies of the drug.

In simple terms, TROPION-Breast02 showed that Dato-DXd may be a more effective alternative to standard chemotherapy for many people with advanced triple-negative breast cancer who cannot receive immunotherapy, helping them live longer while keeping their cancer under control for longer.

OASIS-4

The OASIS-4 study focused on a common but often overlooked challenge for people receiving hormone therapy for breast cancer: hot flushes, night sweats, poor sleep and other menopause-like symptoms. These side effects can be severe and sometimes lead patients to stop taking treatments that are important for reducing the risk of cancer recurrence.

Researchers tested a new non-hormonal medicine called elinzanetant in nearly 500 women with, or at high risk of developing, hormone receptor-positive breast cancer who were experiencing moderate to severe symptoms while taking endocrine (hormone) therapy. Participants received either elinzanetant or a placebo. This drug is considered safe after a diagnosis of breast cancer, because it does not affect the oestrogen receptor.

The results were very encouraging. Women taking elinzanetant experienced fewer and less severe hot flushes and night sweats, with improvements seen as early as the first week and sustained over time. The treatment also led to better sleep and improved quality of life compared with placebo.

Importantly, the drug was well tolerated, with a safety profile consistent with earlier studies. Longer-term analyses presented subsequently showed that benefits were maintained regardless of the type of hormone therapy patients were receiving.

In simple terms, OASIS-4 showed that a non-hormonal treatment may be able to significantly reduce some of the most troublesome side effects of breast cancer hormone therapy, helping patients feel better and potentially making it easier for them to stay on treatment for the recommended length of time.

SERENA-6

The updated SERENA-6 results presented at ASCO 2026 strengthened evidence for a new approach to treating advanced hormone receptor-positive, HER2-negative breast cancer. Researchers regularly monitored patients’ blood for early signs that their cancer was becoming resistant to treatment. When a resistance-related change (an ESR1 mutation) was detected, patients switched to the investigational drug camizestrant while continuing their existing targeted therapy.

The benefits seen in the original analysis were maintained with longer follow-up. Patients who switched early had a median of 16.8 months before their cancer worsened, compared with 9.2 months for those who stayed on standard treatment. The study also showed that benefits extended beyond the first progression, delaying the need for subsequent treatments and more intensive therapies.

Quality of life remained well maintained, and side effects were generally manageable. Researchers also found that cancer-related DNA in the bloodstream was much more likely to disappear in patients who switched to camizestrant, suggesting stronger control of the disease.

In simple terms, SERENA-6 continues to support the idea that regular blood testing may be able to identify treatment resistance before scans show cancer growth. If longer term results are consistent, this may allow doctors to change treatment earlier with the goal of keeping the disease under control for longer.

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