Breast cancer treatments work best when the diagnosis is confirmed early, and the therapy started as soon as possible. But an extensive study on the best way to treat this form of cancer suggests that “precision medicine” does not provide exact answers.
David Hunter, a cancer prevention professor at Harvard’s T.H. Chan School of Public Health, says, “Precision doesn’t mean certainty.”
The study, which involves decisions regarding chemotherapy, hoped to determine if women could avoid having to undergo treatments without raising their risks of recurring cancer, NPR reports.
Like other forms of cancer, treating breast cancer in its early stages before it has spread to other parts of the body, is the most effective way. But Dr. Fatima Cardoso, the lead author and a breast cancer expert at the Champalimaud Clinical Center in Lisbon, Portugal, says the situation creates a problem.
Because the only opportunity to really treat cancer is in its early stages, doctors tend to treat even “when in doubt,” Cardoso says.
So we know that we overtreat the patients with early breast cancer.
This means some women could be getting chemotherapy even if it doesn’t really lower or raise their survival odds.
Cardoso and a team organized a large-scale study throughout Europe to examine whether a genetic test called MammaPrint could reduce overtreatment cases. Over 6,600 women from 112 institutions across nine countries participated.
The researchers looked for women with breast cancer whose physical exams said they were at a relatively high risk of recurrence after surgery, but who also seemed at low recurrence risk based on MammaPrint results.
The women were invited to participate in the study and were randomly assigned to receive chemotherapy or not.
The MammaPrint genomic test studies 70 characteristics of a tumor. It did a thorough job of predicting which among the participants had a low risk of recurrence, according to the research. These women could, therefore, avoid unnecessary pain and risks of chemotherapy. Some American insurance providers have the test covered in their policies.
The study found that 46% of women who were reportedly at high risk of recurrence based on physical exams could skip chemotherapy treatments with little to no risks on their survival rates.
But the tests were not absolute. Around 95% of women who did not have chemotherapy because of their genetic tests did not have recurring cancer five years later. On the other hand, those who did undergo treatment had an estimated 1.5% better health. It will take another massive study to determine if chemotherapy does indeed offer better survival chances.
The researchers raise the point that such precise genetic tests provide probabilities, not hardline data. This applies to the whole of precision medicine, which is marketed as a revolutionary concept in medical care.
Hunter, who wrote an editorial on the study, says, “The new tools will definitely be helpful, but they often will pose challenges about what the right decision is.” He says doctors and patients alike need to accept that there is uncertainty in precision medicine tests and that making decisions based on that 1% odds of survival is a tough call.
Cardoso says the situation is evident in her clinic. Women who have a low genetic risk according to MammaPrint usually skip the chemotherapy. “But there always [are] some patients for whom 1 percent benefit is enough — and you need to respect the wishes of each individual patient,” she says.
The study was published in the New England Journal of Medicine.