(USA TODAY) -- An experimental vaccine prevented breast cancer in genetically engineered mice, according to a preliminary study in the June 10 issue of Nature Medicine. The vaccine has not been tested in humans.
Though the approach is intriguing, it is far too early to know whether a vaccine could also help women avoid breast cancer, says Massimo Cristofanilli, chair of medical oncology at Philadelphia's Fox Chase Cancer Center, who wasn't involved in the experiment.
Many drugs appear promising in mice, but very few succeed in humans, Cristofanilli says.
On average, only one out of every 250 drugs in lab studies or animal models get approved, according to Pharmaceutical Research and Manufacturers of America.
In the new experiment, immunologist Vincent Tuohy at the Cleveland Clinic's Lerner Research Institute tested the vaccine against a protein, called alpha-lactalbumin, found on many breast cancer cells. Mice in the experiment had been genetically modified to lead them to develop breast cancer.
Though none of the 50 vaccinated mice developed cancer, all of the others did.
The protein is not found on normal breast cells, except when women are breast-feeding, the study says. That gives researchers hope that the vaccine would not harm ordinary cells.
But Cristofanilli says testing such a vaccine in humans would be difficult, largely because women at high risk of breast cancer already have several proven options for prevention.
Women who inherit genetic mutations in the BRCA genes - which give women a very high risk of breast cancer - can virtually eliminate their risk through a preventive mastectomy.
Other high-risk women, such as those with a close relative with breast cancer, also can take the drugs tamoxifen or raloxifene to sharply cut their risk.