A new study could hold huge promise for those suffering from cancer: it found that nearly half of women who had been diagnosed with early stage breast cancer can avoid chemotherapy, and there would be little to no risk of the cancer returning.

Using a test of gene activity in tumors, the study could help tens of thousands of women avoid unnecessary chemotherapy. The genomic test measures the genes that control how a cancer grows and spreads, and then determines which women are at a low risk of spread and therefore wouldn’t need chemo, according to the study, which was published in the New England Journal of Medicine.

The study found that 35,000 to 40,000 women each year in the United States could avoid chemo through this test, and 60,000 to 70,000 in Europe.

While doctors have been using genomic tests for about 10 years in breast cancer patients to keep them from having to endure the side effects of chemo, this provides a lot more data on the issue.

“In this randomized, phase 3 study, we enrolled 6693 women with early-stage breast cancer and determined their genomic risk (using the 70-gene signature) and their clinical risk (using a modified version of Adjuvant! Online). Women at low clinical and genomic risk did not receive chemotherapy, whereas those at high clinical and genomic risk did receive such therapy,” the paper states. “In patients with discordant risk results, either the genomic risk or the clinical risk was used to determine the use of chemotherapy. The primary goal was to assess whether, among patients with high-risk clinical features and a low-risk gene-expression profile who did not receive chemotherapy, the lower boundary of the 95% confidence interval for the rate of 5-year survival without distant metastasis would be 92% (i.e., the noninferiority boundary) or higher.

The results are as follows: “A total of 1550 patients (23.2%) were deemed to be at high clinical risk and low genomic risk. At 5 years, the rate of survival without distant metastasis in this group was 94.7% (95% confidence interval, 92.5 to 96.2) among those not receiving chemotherapy. The absolute difference in this survival rate between these patients and those who received chemotherapy was 1.5 percentage points, with the rate being lower without chemotherapy. Similar rates of survival without distant metastasis were reported in the subgroup of patients who had estrogen-receptor–positive, human epidermal growth factor receptor 2–negative, and either node-negative or node-positive disease.”