A low cellular level of a tiny fragment of RNA appears to increase the spread of breast cancer in mouse models of the disease, according to researchers at Whitehead Institute for Biomedical Research.

A team of researchers at Princeton University and The Cancer Institute of New Jersey has identified a long-sought gene that is fatefully switched on in 30 to 40 percent of all breast cancer patients, spreading the disease, resisting traditional chemotherapies and eventually leading to death.

Studies of human tumor cells implanted in mice have shown that the abnormal activation of four genes drives the spread of breast cancer to the lungs. The new studies by Howard Hughes Medical Institute researchers reveal that the aberrant genes work together to promote the growth of primary breast tumors.