A major study about the best way to treat early-stage breast cancer reveals that "precision medicine" doesn't provide unambiguous answers about how to choose the best therapy.
"Precision doesn't mean certainty," says David Hunter, a professor of cancer prevention at Harvard's T.H. Chan School of Public Health.
That point is illustrated in a large study published Wednesday in the New England Journal of Medicine, involving decisions about chemotherapy.
As is true for many cancers, breast cancer responds best to treatment when it is caught early, before it has spread throughout the body. Dr. Fatima Cardoso, the study's lead author and a breast cancer specialist at the Champalimaud Clinical Center in Lisbon, Portugal, says that creates a conundrum for doctors and patients alike.
Because it's the only opportunity to cure the cancer, "when in doubt we tend to treat" women with early-stage breast cancer, she told Shots. "So we know that we overtreat the patients with early breast cancer."
That means that women could end up undergoing chemotherapy even if it wouldn't really improve their survival odds.
Hoping to refine those treatment decisions, Cardoso helped organize a huge study throughout Europe to see whether a commercially available genetic test called MammaPrint could help reduce that overtreatment. More than 6,600 women participated at 112 institutions in nine nations.
Scientists identified women with breast cancer whose physical exams suggested they were at relatively high risk for having the cancer return eventually after surgery, but who seemed to be at low risk of recurrence based on the genetic test results.
They were invited to participate in the study, which would randomly assign them to have chemotherapy or not. "You know that chemotherapy is a treatment that scares people, so overall and for the majority of patients, it was not difficult to convince them," Cardoso says.
The genomic test, which studies 70 distinct features of a tumor, did a pretty good job of predicting who was at low risk for recurrence of breast cancer and could therefore avoid the pain, discomfort and risks of chemotherapy. (The test, priced at $4,200, is covered by some insurance in the United States.)
The scientists found that 46 percent of women who were deemed to be at high risk of recurrence based on physical symptoms could actually skip chemotherapy with little consequence to their long-term survival.