For many people diagnosed with breast cancer, one of the biggest fears is chemotherapy.
While chemotherapy can save lives, it often comes with difficult side effects such as fatigue, nausea, hair loss, infections, and long-term health problems.
Doctors have long known that some patients benefit greatly from chemotherapy, while others receive little extra benefit but still experience its physical and emotional burden.
Now, a major international study suggests that many people with a common type of breast cancer may be able to safely avoid chemotherapy altogether.
The research was led by scientists at University College London (UCL) and involved more than 4,400 patients from several countries, including the United Kingdom, Australia, New Zealand, Norway, Sweden, and Thailand.
The findings were presented at the 2026 American Society of Clinical Oncology meeting and are expected to influence future cancer treatment decisions.
The study focused on hormone-sensitive breast cancer, the most common form of the disease. This type of cancer grows in response to hormones such as estrogen. Patients in the study were aged 40 and older, and most had cancer that had already spread to nearby lymph nodes.
Because lymph node involvement increases the risk of the cancer returning, many of these patients would normally be advised to receive chemotherapy in addition to hormone therapy.
Researchers wanted to find out whether a genomic test called Prosigna could identify which patients truly needed chemotherapy. The test examines the activity of specific genes inside tumor cells and provides a score that estimates the risk of the cancer returning.
Unlike some other genetic tests, Prosigna can be performed in hospitals that have the necessary laboratory equipment, making it more practical for widespread use.
The OPTIMA trial randomly assigned patients to different treatment approaches. One group received the standard treatment of chemotherapy followed by hormone therapy.
The second group received treatment based on their Prosigna test results. Patients with high scores received chemotherapy and hormone therapy, while those with low scores were treated with hormone therapy alone.
The results were encouraging. More than two-thirds of patients had low Prosigna scores. Five years after treatment, 94.8% of low-score patients who received chemotherapy remained alive and free of cancer recurrence. Among those who skipped chemotherapy and received hormone therapy alone, 93.6% remained alive and recurrence-free.
The difference between the two groups was very small. Statistical analysis suggested that only a tiny percentage of low-score patients might benefit from chemotherapy. For the vast majority, chemotherapy appeared to offer little additional advantage.
This finding could have a major impact on patient care. Researchers estimate that more than 5,000 patients in the UK’s National Health Service each year could safely avoid chemotherapy. Similar benefits could extend to many thousands more patients worldwide.
The study is particularly important because it included groups often underrepresented in previous research. Earlier studies mainly focused on postmenopausal women with limited lymph node involvement.
In contrast, OPTIMA included premenopausal women and patients whose cancer had spread to several lymph nodes. Researchers found similar results across these different groups.
One patient in the study, Karen Bonham from Cardiff, was preparing to begin chemotherapy when her Prosigna test results arrived. The results showed she did not need chemotherapy. Instead, she received radiotherapy and hormone therapy. Nearly nine years later, she remains healthy and active.
The research was published and presented as one of the largest studies of its kind. However, researchers note that questions remain. The findings do not yet apply to people younger than 40 years old, and additional research is needed for some patient groups. There were also too few men in the study to draw firm conclusions about male breast cancer.
Overall, the findings represent an important step toward personalized medicine. Rather than treating all patients in the same way, doctors can use information from a tumor’s genetic activity to make more precise treatment decisions.
The study shows that many patients may be spared the physical, emotional, and financial costs of chemotherapy without reducing their chances of survival.
Study analysis: The findings are strong because they come from a large randomized clinical trial involving thousands of patients across multiple countries. The results suggest that tumor biology may be a better guide to treatment decisions than traditional risk factors alone.
While longer follow-up and further studies will still be valuable, the evidence indicates that Prosigna testing could safely reduce unnecessary chemotherapy for many patients and improve quality of life while maintaining excellent cancer outcomes.
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Source: University College London (UCL).
