The breast cancer gene in question, called SATB1, bosses other breast cancer genes and hushes anticancer genes.
Those findings come from lab experiments done in test tubes and mice; further studies are needed in people.
To put SATB1's influence in perspective, the new lab tests show that switching off SATB1 affected more than 1,000 genes.
In addition to being a potential target for new breast cancer treatments, SATB1 might predict the odds that early-stage breast cancer will spread, according to the researchers.
They included Hye-Jung Han, PhD, and Terumi Kohwi-Shigematsu, PhD, of the Lawrence Berkeley National Laboratory at the University of California, Berkeley.
The study appears in the March 13 edition of Nature.