CHICAGO — A University College London-led international study found that a DNA test can identify early-stage breast cancer patients who do not benefit from chemotherapy, potentially sparing more than two-thirds of them from the treatment’s side effects. The findings will be presented at the American Society of Clinical Oncology’s annual meeting in Chicago on Saturday.

The study involved more than 4,000 newly diagnosed breast cancer patients over the age of 40 across the UK, Norway, Sweden, Australia, New Zealand, and Thailand. Researchers used a gene test called Prosigna to analyze the activity of 50 genes linked to breast cancer growth and calculate each patient’s risk of recurrence. Patients with a low Prosigna score—comprising two-thirds of participants—did not receive chemotherapy and were treated with hormone therapy alone.

Among those with low scores who avoided chemotherapy, the five-year survival rate was 93.7%, compared to 94.9% for patients who received chemotherapy. University College London said the results suggest more than 5,000 NHS patients annually could safely forgo chemotherapy. It is not known whether the findings apply to patients under age 40, with results for that group still several years away, according to the university.

Chemotherapy is commonly recommended after surgery for early-stage breast cancer that has spread to nearby lymph nodes, though clinicians have expressed concern it offers little benefit to patients with the most common type of breast cancer. The treatment can cause fatigue, nausea, hair loss, a weakened immune system, and fertility issues.

Professor David Miles said, “We used to give chemotherapy to 100 women to benefit 10, knowing that 90 didn't need it. We can now confidently predict many patients will get no benefit at all, and therefore there's no need for them to have the chemotherapy.”

Karen Bonham, from Cardiff, avoided chemotherapy thanks to the Prosigna test and instead received radiotherapy and hormone therapy over eight years. “Cancer diagnosis and treatment can be shocking. It certainly propels you into a world of uncertainty. Life priorities realign—you simply want to survive,” Bonham said.

Tanya Hutson, diagnosed with breast cancer in 2022, called the test “absolutely amazing” and described chemotherapy as “brutal.” She said, “It just proves what happens when money is put into research.”