“The trial results provide an unprecedented level of evidence and precision to guide the use of chemotherapy in women with early-stage breast cancer,” says Dr. Sparano, a professor of medicine and of obstetrics & gynecology and women’s health at Einstein and the vice chair of the ECOG-ACRIN Cancer Research Group, a cancer clinical trials group. “We now know that the large majority of such women—those facing an intermediate risk for cancer recurrence—don’t need chemo.”

After surgery, breast cancer patients commonly receive chemotherapy as a precaution against often-fatal cancer recurrence—even patients considered at low risk for recurrence and for whom chemo’s benefits were uncertain. To guide their use of chemo, doctors use a 21-gene expression test, the Oncotype DX assay, which yields a score indicating a low, intermediate, or high risk that a woman’s breast cancer will recur.

About two-thirds of women who are tested—an estimated 65,000 each year in the United States—receive an intermediate-range recurrence score. Whether chemo helps them was uncertain, yet often they received it as a precaution. A major goal of TAILORx was to discover whether chemo helps them.

The trial recruited nearly 10,300 early-stage breast cancer patients, at more than 1,000 sites worldwide, who had undergone surgery. Their cancers had not spread to lymph nodes and were hormone-receptor positive (i.e., their growth was fueled by hormones) and HER2-negative (i.e., they would not respond to the drug Herceptin).

At the start of the trial, each participant’s tumor tissue was tested using the Oncotype DX assay. Patients with low recurrence scores (0 to 10) were assigned to receive endocrine therapy alone. Patients with high recurrence scores (26 to 100) were assigned chemotherapy plus endocrine therapy, based on evidence that women with high recurrence scores clearly benefit from chemotherapy. The largest group—the 6,700 with intermediate recurrence scores of 11 to 25—were randomly assigned to receive chemotherapy plus endocrine therapy or endocrine therapy alone.

The  TAILORx findings show that women at intermediate risk for recurrence did not benefit from chemotherapy. After nine years, 93.9 percent of the women in the endocrine-only group were still alive, versus 93.8 percent of women in the endocrine-plus-chemo group.