Estrogen can help breast cancer cells invade the blood stream and spread around the body, according to a new study by Cancer Research UK scientists in Wales.

Dr. Wen Jiang and his team from the University of Wales College of Medicine in Cardiff studied the effect of estrogen on cells that line our blood vessels. They found the hormone made the vessels leaky, making it easier for cancer cells to slip through.

And they believe designing treatments to counteract the effect of estrogen and strengthen the blood vessel wall could stop rogue cancer cells from getting into circulation and reaching other organs in the body.

Cancer spreads to other parts of the body when a cell breaks away from the primary tumor and enters a surrounding blood vessel.

According to Jiang: "We already knew estrogen could help some breast cancers to develop by stimulating the growth of cells. As a tumor develops, the chance of a cell breaking away and traveling to another part of the body increases. But this is the first study to show that estrogen affects the cells which line our blood vessels."

In the lab, the researchers created a mini-wall of blood vessel cells. Using a fluorescent chemical they visualized how much of it leaked from one side of the wall to the other. When they added estrogen and repeated the experiment, the cells became substantially more leaky.

They think the hormone makes blood vessel cells more permeable by stopping structures, called tight junctions, from working properly. Tight junctions act like glue sealing our cells together.

To test their theory the team analyzed the levels of the glue-like structures in blood vessel cells and found they dropped after estrogen was added.

Scientists believe without this glue, the links between blood vessel cells are weaker, making it easier for cancer cells to get through.

At the end of last year, Jiang's team found breast cancer patients with low levels of the glue are more prone to disease spread.

Jiang says: "It seems that estrogen disrupts these glue-like structures that lie between the cells in our blood vessels, creating opportunities for breast cancer to spread to other parts of the body.

"We are currently looking at ways to boost the levels of tight junctions in patients to see if this can help halt the rapid spread of the disease."

Professor Robert Souhami, Director of Clinical Research at Cancer Research UK, says: "There are currently very effective methods to manage cancer confined to the breast but treatment becomes more difficult when abnormal cells spread to other parts of the body.

"This study has provided us with valuable clues on how it might be possible to contain the disease in its early stages and improve the chances of successful treatment."

SOURCES:
Journal of Cellular Physiology, Vol. 196, Issue 2
Cancer Research UK (http://www.cancerresearchuk.org)