For aggressive, intractable triple-negative breast cancers, there’s still hope. Researchers at the Mayo Clinic found that a pre-existing drug that’s shown positive effects in another type of breast cancer may also halt the spread of triple-negative cancer.
Breast cancer is generally classified into 3 subtypes according to the presence or absence of three receptors: estrogen, progesterone, and the epidermal growth factor receptor 2 (HER2). Typically, breast cancers positive for estrogen or HER2 respond well to hormone therapy. However, cancers that are negative for these receptors have proven more difficult to treat and manage. In particular, cancers that are negative for all three receptors, known as triple negative breast cancer, are most notorious for evading treatment.
In studying how the receptor-positive breast cancers respond to treatment, researchers at the Mayo Clinic found that a class of inhibitors may also be effective against receptor-negative breast cancers.
The drugs are known as CDK 4/6 inhibitors, and they work by blocking the enzyme cyclin-dependent kinases (CDKs). Many cancers have high CDK activity, which promotes the unregulated proliferation of cancer cells. Inhibitors of this enzyme pathway have been shown to be effective against ER-positive and HER2-positive breast cancers. Recently, Palbociclib – another CDK 4/6 inhibitor – showed promising Phase II trial results in patients with HER2-negative breast cancer too.
CDK 4/6 inhibitors have previously been tested in triple-negative breast cancers with disappointing results – these drugs didn’t seem to reduce the growth of these cancers. But in applying the drugs to a triple-negative breast cancer mouse models, researchers at the Mayo Clinic found that metastasis was halted. In essence the drug stopped the cancer from invading to other parts of the body.
Of note, metastasis is one of the biggest conditions that severely undermines the effectiveness of anticancer treatments. As such, a drug that can halt metastasis is still quite important, even if it can’t reduce the growth of the primary tumor. Perhaps this will lead to combination therapy that targets both the primary tumor and prevent spread to secondary organs, thereby increasing the survival rate.
"These findings may provide a new treatment for the prevention of cancer metastasis. Mayo Clinic is now developing new studies that will focus on the role of CDK 4/6 inhibitors and their potential to inhibit cancer metastasis in women with triple-negative breast cancer who are at highest risk for cancer metastasis,” said Matthew Goetz, the study’s co-author.