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"Many patients dread the idea of chemotherapy, and by avoiding it they can substantially reduce the stress involved in having cancer, as well as improve their overall quality of life," said Dr. Sabine Linn from the Netherlands Cancer Institute.
By testing a breast cancer tumour for its genomic signature, doctors can avoid what's called adjuvant chemotherapy in 30% of cases, the study found.
Adjuvant chemo is usually done post-surgery to destroy any microscopic cancer cells that may have been missed in the operation. It works, but the side-effects can be quite painful.
The researchers looked at follow-up data from 427 cancer patients involved in a previous study whose cancers had not yet spread to the lymph nodes. By looking for a particular selection of 70 genes in a tumour, the test, dubbed Mammaprint, can predict which patients are at low and which at high risk of metastasis, the process of cancer spreading from one area to another.
The Mammaprint test determined that 219 patients were at low risk for metastasis. Of those, 15% went on to receive chemo. Of the 208 deemed at high risk, 81% underwent chemotherapy.
Five years later, 96% of patients in the low-risk group survived cancer-free, compared to 91% in the high-risk group.
"It is encouraging to be able to tell patients that we believe they will have just as good a chance of avoiding the recurrence of cancer by not having adjuvant chemotherapy as by having it," Linn said.