COLUMBIA, Mo., May 13 (UPI) -- U.S. researchers say animal models indicate hormone therapies may increase the chance of breast cancer metastasis.
Researchers at the University of Missouri in Columbia said metastasis -- the spreading of cancer beyond the lymph nodes -- was more likely when taking the hormone progestin. Progestin is a hormone used to counteract the potentially negative effects of estrogen therapy.
"In our study, we found that progestins increase the number of blood vessels that are responsible for transporting existing cancer cells," Salman Hyder says in a statement. "The more the blood vessels increase, the higher the chance of cancer cell metastasizing."
Hyder says the negative effect of progestins was worse in the absence of a protein that suppresses tumors called P53.
The researchers tested several different progestins on breast cancer tumors in an animal model. They found all types acted similarly to increase the likelihood of cancer spread.
Hyder's study has been accepted for publication in Menopause: The Journal of The North American Menopause Society.