The study led by Salman Hyder, professor of biomedical sciences in the College of Veterinary Medicine and the Dalton Cardiovascular Research Centre has found that one of the hormones used in HRT also known as synthetic progestin may increase the risk of developing breast cancer among women.
However, using an antibody known as PRIMA that prevents new blood vessel formation in tumours may effectively treat or prevent the effects of progestin.
"As women age, many develop tiny lesions in their breasts," said Hyder.
"The majority of the time, these lesions never expand. We think this might be due to a specific protein, p53, that, under normal circumstances, prevents tumour cells from living.
"We found in our study that when the protein is active, it reduces the number of breast cancer cells in the body by inhibiting the growth factor that supplies blood vessels to the tumour.
"However, when the cells of these lesions are exposed to progestin in a body that does not have an active p53 protein, we found that the cells might start expanding and turn into tumours," he added.
The research was conducted using animal models where the animals carrying breast cancer cells were exposed to synthetic progestin known as medroxyprogesterone acetate (MPA).
The findings revealed that MPA exposure accelerated the growth of breast cancer cells, however, when the team exposed the cells to the antibody known as 2C3, or PRIMA, that inhibited formation of new blood vessels in tumours, the tumour cells failed to grow and spread in response to the MPA.
"Since MPA is a synthetic hormone, it stays in the body longer," Hyder said. "Unfortunately, while the drug is used to protect the uterus from the harmful effects of estrogens in HRT formulations, it is hurting the breast."
The study is published in the journal, Cancer Research.