The existing drug estradiol can inhibit tumor growth in a subtype of triple-negative breast cancer. The researchers may soon test the repurposed drug in a phase II clinical trial, Medical News Today reports.
Triple-negative breast cancer is an aggressive form of breast cancer wherein tumors lack expression of three proteins.
The three are estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 (HER2).
Triple-negative breast cancer is able to grow and spread more quickly than other forms of breast cancer.
Also, because its cancer cells lack hormone receptors, specialists cannot treat them with hormone therapy. The only treatment for these types of cancer is chemotherapy.
New research, however, has revealed that an existing drug could be repurposed to treat some of the people with this form of breast cancer.
Researchers led by John Hawse, Ph.D., a molecular biologist at the Mayo Clinic in Rochester, MN, tested the effects of estradiol on a subtype of triple-negative breast cancer tumors.
"Triple-negative breast cancer is a form of breast cancer that lacks expression of estrogen receptor alpha, progesterone receptor, and [HER2]," explains Hawse, who adds that the condition "exhibits high rates of disease recurrence."
However, previous research by Hawse and team found that another form of estrogen receptor — called estrogen beta — is present in 25 percent of triple-negative tumors, as well as in over 30 percent of estrogen receptor-positive breast cancer tumors.
That research also showed that the estrogen receptor beta is a tumor suppressor, which correlates with better patient outcomes.
In their new study, Hawse and his colleagues studied the effect of estradiol on the growth of triple-negative tumors that express estrogen receptor beta. The study included both in vitro and in vivo experiments.
"Remarkably," claims Hawse, "we discovered that estradiol, which normally stimulates [the] growth of cancer cells in tumors that express estrogen receptor alpha, has the opposite effect in triple-negative breast cancer."
"However, estradiol was only able to inhibit the growth of triple-negative breast cancer when estrogen receptor beta was present," he adds.