Ten years after their diagnosis, 3.2% women who'd had radiation after lumpectomy had gone on to get a mastectomy, compared to 6.3% in the group that did not receive radiation.
When researchers dug deeper into the numbers to try to learn which women were getting the most benefit, they found that it was women aged 70 to 75 who had high-grade tumors. A tumor's grade refers to the way its cells look under a microscope. High-grade tumors have very abnormal-looking cells.
Patients in the study with high-grade tumors who chose not to get radiation therapy after their surgeries had a 15% chance of having a mastectomy within 10 years.
Women over 75 with tumors that didn't look very aggressive didn't appear to benefit from radiation.
Guidelines Say Radiation Doesn’t Benefit Most Older Patients
Breast cancer becomes more likely with age. The majority of breast tumors are fueled by hormones, and most breast cancers are caught early, before they've spread to the lymph nodes or other organs.
"There are lots of patients like this that we see in our clinic all the time," says researcher Benjamin Smith, MD, an assistant professor in the radiation oncology department at MD Anderson Cancer Center in Houston.
Since 2005, the nonprofit National Comprehensive Cancer Network has advised against radiation therapy after surgery to remove early estrogen-sensitive breast cancers in women in their 70s.
The guidelines are based on an earlier study that found radiation didn't reduce mastectomies or improve survival for women in their 70s who were taking the drug tamoxifen to lower their risk of getting breast cancer again.
"The message of this [new] study is that you maybe can't apply these guidelines to every patient," Smith says. "Especially for patients who are younger or who have high-grade tumors, there's still probably a benefit from radiation that's worth discussing with them."