A new genomic test could allow the majority of people with early breast cancer to safely skip chemotherapy and its grueling side effects, according to results from a 4,000-patient international trial released this week.
The test, called Prosigna, measures the activity of 50 genes linked to breast cancer growth and uses the pattern to calculate how likely a tumor is to come back. In the trial, patients who scored low — about two-thirds of the group — were treated with hormone therapy alone and never received chemotherapy. Their five-year survival rate was 93.7%, essentially indistinguishable from the 94.9% seen in patients who did receive chemo.
For a disease that affects more than two million people a year worldwide, that small statistical gap translates into potentially millions of patients spared the hair loss, nausea, fatigue, infections and lasting nerve damage that chemotherapy can bring.
From "treat everyone" to "treat the right people"
Until recently, doctors managing early breast cancer faced a difficult tradeoff. Because they could not reliably tell which tumors would relapse, many patients received chemotherapy as a precaution — even those whose cancers might never have come back without it. The result was over-treatment on a vast scale.
Genomic tests like Prosigna change that calculation. By looking directly at the biology of each tumor, the test sorts patients into low- and high-risk groups, helping clinicians and patients decide together whether the benefits of chemotherapy outweigh the costs.
"Our findings show that many patients can safely avoid chemotherapy without compromising their outcomes," said trial lead Professor Rob Stein of University College London's Cancer Institute. "For patients, this means many may be spared the physical and emotional burden of chemotherapy and its potential long-term side effects. For health systems, it represents a more efficient and evidence-based use of resources."
How the test works
Prosigna analyzes RNA extracted from a small piece of preserved tumor tissue and runs it through a digital gene-expression platform that scores 50 cancer-related genes. The algorithm sorts tumors into established molecular subtypes — Luminal A, Luminal B, HER2-enriched and basal-like — and produces a risk-of-recurrence score from 0 to 100.
That score, combined with traditional factors like tumor size and lymph node status, gives oncologists a far more personalized picture than tumor measurements alone. The trial enrolled both men and women across multiple countries, and the result held across age groups and tumor sizes.
Less treatment, same outcome
The five-year results are particularly striking because the patients who skipped chemotherapy were not a hand-picked subset. They were the majority — roughly two-thirds of everyone enrolled — and their survival was statistically the same as those who received the full regimen. That is the gold-standard result that genomic testing advocates have been seeking for years.
"This is a really important step toward truly personalized cancer treatment," said one oncologist who reviewed the data. "We're moving away from blanket protocols and toward decisions made by your tumor's genes, not by an average."
What happens next
Health systems in the UK, Europe and parts of Asia already use genomic tests in some breast cancer cases, but coverage is uneven. The new trial strengthens the case for making such tests standard for all early-stage hormone-receptor-positive patients — a change that researchers say could save healthcare systems hundreds of millions of dollars while improving patients' quality of life.
For people newly diagnosed with breast cancer, the bottom line is simple and hopeful: in the coming years, fewer of them may need chemotherapy at all, and the ones who do will be the ones who actually need it.
