Researchers may be one step closer to preventing triple-negative breast cancer, the most aggressive subtype of breast cancer, from spreading elsewhere in a person. Ibrance (palbociclib), an FDA-approved drug for estrogen receptor-positive breast cancer, could also effectively block metastasis in triple-negative breast cancers, they report. The drug, however, did not affect growth in the original tumor. The study, "CDK4/6-dependent activation of DUB3 regulates cancer metastasis through SNAIL1," was published in Nature Communications. "Metastasis is a hallmark of cancer and a leading cause of cancer death," Zhenkun Lou, PhD, of Mayo Clinic, the study's senior author, said in a press release. "Despite great progress in cancer therapy, the prevention of cancer metastasis is still an unfulfilled challenge." Lou and his team had a hint that inhibiting CDK4/6, which regulates a cancer metastasis protein, could influence the transition of immotile cancer cells into migratory cells — a process called epithelial-to-mesenchymal transition (EMT). They focused particularly on triple-negative breast cancer cells because such cancers are known to grow the fastest and to be more metastatic than any other breast cancer subtype. "Prior published data suggested that CDK 4/6 inhibitors were not effective in reducing the growth rates of estrogen receptor negative breast cancer," said Lou. "Our data confirmed that, while the rate of growth of triple-negative breast cancer was not affected by CDK 4/6 inhibitors, this class of drugs was able to significantly inhibit the spread of triple-negative breast cancer to distant organs when tested in multiple different triple-negative breast cancer models." This was true not only in triple-negative breast cancer cells cultured i