More women with early-stage breast cancer may be able to safely skip chemotherapy after having surgery, according to initial results from a major clinical trial.
The trial, conducted in nine countries, found that adding chemotherapy to hormone-blocking drugs brought no added benefit to a particular group of patients. Those were postmenopausal women with hormone-sensitive breast cancer that had spread to only one to three lymph nodes, and who had a low risk of recurrence.
In contrast, researchers found, chemo did help younger, premenopausal women -- reducing their risk of a breast cancer recurrence over five years.
Experts predicted the results will change medical practice, freeing thousands of women each year from the toxic side effects of chemotherapy.
"Knowing who does and does not benefit from adjuvant chemotherapy is powerful information for the individual women and cannot be overemphasized," said Dr. Charles Shapiro, an oncologist who was not involved in the trial.
The findings should "de-escalate" treatment for many postmenopausal women, said Shapiro, a professor and director of translational breast cancer research at Mount Sinai's Icahn School of Medicine in New York City.
On the other hand, he said, the results should give premenopausal women more confidence that they stand to benefit from adjuvant chemo.
"Adjuvant" refers to chemotherapy given after breast cancer surgery, with the goal of warding off a recurrence.
But recent research has revealed that many women can skip it.
In 2018, a trial hailed as "groundbreaking" showed that many women with the most common type of breast cancer did not need post-surgery chemo.
Specifically, the trial included women with breast cancer that was hormone-receptor-positive -- meaning estrogen helps it grow -- but negative for receptors for the protein HER2. Most breast cancers fall into that category.
In addition, trial participants had a low risk of recurrence, as judged by a test called Oncotype DX, which analyzes certain tumor genes. And their tumors had not spread to any lymph nodes.
That left a question open: What about women whose cancer has spread to just a small number of lymph nodes? The new trial was designed to provide answers.
It's "critical" to better understand when to use adjuvant chemo, said trial leader Dr. Kevin Kalinsky, director of the Glenn Family Breast Center at Emory University's Winship Cancer Institute in Atlanta.
"Our goal is to offer patients 'precision medicine,' " he said. That, he added, includes avoiding any "overtreatment" with therapies that are unlikely to help, but can cause toxicities.
Chemotherapy can carry side effects like hair loss, fatigue, and nausea and vomiting, as well as potentially lasting damage to the heart or nerves, and problems with memory and other mental skills -- often called "chemo brain."
The new trial involved more than 5,000 women with hormone-sensitive, HER2-negative breast cancer that had spread to one to three lymph nodes. All had a relatively low risk of a cancer recurrence, based on the Oncotype DX test.
The test gives a score ranging from 0-100; women in the trial had scores of 25 or less.
Kalinsky's team randomly assigned the women to receive hormonal therapy alone or hormonal therapy plus several months of chemo.
For postmenopausal women, chemotherapy made no difference in the odds of recurrence over five years. About 92% stayed recurrence-free, whether they had chemo or not.
The story was different for premenopausal women. About 94% of those on chemo plus hormonal therapy remained recurrence-free, versus 89% of those on hormonal therapy alone.
It's not clear why, Kalinsky said, though one possibility is the more aggressive nature of breast cancer in younger women.
Questions about the long term remain. In this type of breast cancer, Shapiro said, more than half of recurrences occur beyond the five-year mark.
Kalinsky acknowledged that and said the trial patients will be followed for 15 years. But he also said his team anticipates the results will hold up.
"I do think these data will be practice-changing," Kalinsky said.
The trial was partly funded by the U.S. National Cancer Institute. In a statement, the NCI's Dr. Larissa Korde called the study "an important step toward the goal of matching patients with the most appropriate therapies and ensuring that patients do not receive treatments that are unlikely to benefit them."
The findings were scheduled to be presented Thursday at the San Antonio Breast Cancer Symposium, being held online. Such research is generally considered preliminary until published in a peer-reviewed journal.
The American Cancer Society has an overview of breast cancer treatments.
SOURCES: Kevin Kalinsky, MD, MS, director, Glenn Family Breast Center, Winship Cancer Institute of Emory University, Atlanta; Charles Shapiro, MD, professor, medicine, and director, translational breast cancer research, Icahn School of Medicine at Mount Sinai, New York City; U.S. National Cancer Institute, news release, Dec. 9, 2020; online presentation, San Antonio Breast Cancer Symposium, Dec. 10, 2020