A genomic test could help thousands of breast cancer patients avoid chemotherapy without compromising their outcomes, according to results from a large international phase III clinical trial presented at the American Society of Clinical Oncology (ASCO) Annual Meeting in Chicago.

The study, known as OPTIMA, enrolled more than 4,400 patients with hormone receptor-positive, HER2-negative early breast cancer. This subtype accounts for the majority of breast cancer diagnoses worldwide and is often treated with surgery followed by hormone therapy and, in many cases, chemotherapy.

Researchers used the Prosigna Breast Risk of Recurrence test to determine which patients were likely to benefit from chemotherapy and which could safely skip it. The test analyzes the activity of 50 genes in a tumor sample and generates a score that estimates the risk of the cancer returning.

The trial was led by University College London and supported by the UK’s National Institute for Health and Care Research. Patients were randomly assigned to receive either standard treatment decisions or treatment guided by the genomic test.

Genes replace guesswork

For decades, oncologists have relied on tumor size, grade, lymph node involvement, and other clinical factors when deciding whether to recommend chemotherapy. While these indicators remain important, they do not always accurately predict who will benefit from treatment.

The OPTIMA trial was designed to determine whether genomic information could improve those decisions and reduce unnecessary chemotherapy use.

Patients classified as higher risk by the Prosigna test received chemotherapy alongside hormone therapy. Those categorized as lower risk were treated with hormone therapy alone.

According to the trial findings, outcomes among lower-risk patients were nearly identical regardless of whether chemotherapy was used. The results suggest that many patients can avoid chemotherapy and its side effects without increasing the likelihood of cancer recurrence.

“OPTIMA addresses a longstanding challenge in breast cancer care: identifying who truly benefits from chemotherapy and who does not. Our findings show that many patients can safely avoid chemotherapy without compromising their outcomes,” said Professor Rob Stein, chief investigator of the trial and professor of breast oncology at University College London. (The Guardian)

The researchers believe the findings could significantly change how treatment decisions are made for patients with early-stage breast cancer.

Chemotherapy remains an important tool in cancer treatment, but it can also cause severe side effects, including fatigue, nausea, hair loss, nerve damage, infertility, and long-term impacts on quality of life. Identifying patients who are unlikely to benefit from the treatment could help spare them these risks.

Personalized cancer care

The Prosigna test was developed by cancer diagnostics company Veracyte, which said the results provide some of the strongest evidence yet supporting genomic-guided treatment decisions.

“The OPTIMA trial results represent a major milestone in precision breast oncology and will provide Level 1A evidence supporting Prosigna-guided treatment decisions,” said Kelly Marcom, medical director for breast cancer at Veracyte.

The company said the findings support a growing shift toward precision medicine, where therapies are tailored to the biological characteristics of an individual’s disease rather than applying the same treatment approach to all patients with similar clinical features.

“These findings have the potential to transform how clinicians treat a large population of patients with breast cancer, helping them to personalize their patient’s treatment choices using the genomic insights that the Prosigna test provides,” Marcom added.

Researchers also noted that reducing unnecessary chemotherapy could benefit healthcare systems by lowering treatment costs and minimizing the burden associated with managing side effects.

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