The new test, called the MammaPrint test, comes from Agendia Laboratories in Amsterdam, Netherlands, a spin-off of the Netherlands Cancer Institute.
If the test says a woman is at low risk, she has a 95% chance of remaining cancer-free after five years and a 90% chance of remaining cancer-free after 10 years -- without chemotherapy.
If the test says a woman is at high risk, she has a 23% chance of having her cancer come back within five years and a 29% chance of having her cancer come back after 10 years. These women are more likely to need chemotherapy.
Studies suggest the test would cut the number of women who have to undergo breast cancer chemotherapy by 20% to 30%.
However, the decision of whether or not to undergo chemo should be based on other clinical and diagnostic factors in addition to the MammaPrint test, says Steven Gutman, MD, director of the FDA's Office of In Vitro Diagnostic Device Evaluation.
"This test provides powerful new insight into the behavior of the tumor. But you cannot go all the way to the bank with this test," Gutman said in a news conference.
"This is a good test but not a perfect test," he said.
To get a MammaPrint test, a doctor sends the Amsterdam lab a piece of the breast tumor removed during surgery.
The lab uses a computerized tool, called a microarray, that tests the tumor for activation of 70 different genes linked to breast cancer.
Gutman says the lab returns results in about two days.
MammaPrint was tested on 307 women under age 61 who underwent surgery for stage I or stage II breast cancer that had not spread to the lymph nodes. That study showed the test more than doubled doctors' ability to predict breast cancer recurrence.
A major clinical trial is now testing whether the test really helps women avoid needless chemotherapy. The European study will recruit 6,000 women with early-stage breast cancer.