For patients facing a diagnosis of early stage breast cancer, the traditional course of treatment is typically surgery, followed by an often difficult course of chemotherapy to try to make sure the cancer doesn’t recur.
But, a new study published Wednesday in the New England Journal of Medicine found that about 46% of women who were at high risk of breast cancer recurrence after surgery might not actually need chemotherapy — which often comes with debilitating side effects like profound fatigue, nausea, hair loss, and a weakened immune system.
This was the result of a five-year-long clinical trial of about 6,700 women who had been diagnosed with early-stage breast cancer. It was run by Agendia, a company that makes a diagnostics test called “MammaPrint” that screens breast cancer tumours for the activity in 70 genes. The results of the test are designed to give cancer doctors an idea of whether someone is at a low or high genetic risk for recurrence.
Laura Van t’ Veer, one of the lead authors of the study and chief research officer at Agendia, likened the genetics of the tumour to an engine, while age or other measures of risk of recurrence were more like the body of a car. You could have a fancy car with a bad engine, which means you might overlook someone who would benefit from chemotherapy. Or, you could have an old car with a fantastic engine, which means the chemotherapy might not be needed.
“It’s only when you look under the tumour, you see what the aggressiveness of the tumour is,” she told Business Insider. That’s what the MammaPrint test aims to do.
The researchers looked at the group of patients that might have a shabby looking car but a solid engine (those with high clinical risk but low genetic risk, as determined by the MammaPrint test). They found that 1,550 people in the group fit that criteria, and randomly assigned them to either get chemotherapy or not.
By the end of the five-year study, they found that the overall survival was only 1.5% better for those who had chemotherapy over those who didn’t, which Van t’ Veer said the group found “not statistically significant.”
In an accompanying editorial, the American Society of Clinical Oncology agreed that the MammaPrint test seemed to be a good tool for helping patients steer clear of chemotherapy when it might be unnecessary. But they cautioned against dismissing that 1.5% increase in the survival rate of the chemotherapy group.
“These findings provide evidence that the genomic test can reassign some classically high-risk patients with early-stage breast cancer to a lower-risk cohort in whom any plausible chemotherapy benefit would be modest,” they wrote. “However, a difference of 1.5 percentage points, if real, might mean more to one patient than to another. Thus, the stated difference does not precisely exclude a benefit that clinicians and patients might find meaningful.”
Agendia isn’t the only test that helps doctors determine whether a breast cancer patient needs chemotherapy — Onocotype DX, made by GenomicHealth, is another similar test that’s been widely used and studied. Van t’ Veer said the main difference between the two competing tests was that Oncotype DX focuses on who would benefit from chemotherapy, while MammaPrint takes the opposite approach by trying to pinpoint who should definitely not get chemotherapy.
Dr. Harold Burstein, an oncologist at Dana-Farber Cancer Insititute who wasn’t involved in the research, told Business Insider that the trial wasn’t enough to convince him to switch him over from Oncotype DX. That 1.5% benefit that patients who received chemotherapy got after showing a low genetic risk was one of the main sticking points for him. And patients must be followed for more than five years to see the long-term results.
But overall, the trial was good news.
“It supports the general idea that genomic information can add to traditional pathology,” he said.
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