Lymph vessels help cancer spread, researchers say

By: Maggie Fox,
Health and Science Correspondent

WASHINGTON (Reuters) - Tumors grow tiny lymph vessels that help them spread throughout the body --
a surprising finding that could help in the treatment of
cancer, researchers said Wednesday.

Cancer cells were known to spread through the body's normal system of lymph nodes and vessels, but the tumors manage to grow their own as a kind of escape route, three separate teams of researchers found.

"We have identified a mechanism of breast cancer metastasis," Dr. Michael Detmar, a dermatologist who led one of the studies, at Massachusetts General Hospital, said in a statement.

"I wouldn't say it's the mechanism because there may be several others. But this is certainly a major molecular mechanism of how breast cancer metastasizes to the lymph nodes."

Other teams of researchers said they identified proteins that cancer cells use to build their little lymph vessels, and also a possible way to block this.

Detmar's team used a new method for imaging lymphatic vessels, which previously could not be seen in tumors. They found a "marker" -- a gene called LYVE-1 that is expressed or active in lymph vessels.

Writing in the journal Nature Medicine, they said they saw networks of lymphatic vessels inside breast tumors grown in mice. They seemed to be carrying tumor cells.

And the more lymphatic vessels there were in the tumors, the more metastatic cells had spread to the lymph nodes and lungs.

This might help doctors predict whose cancer is likely to spread and thus who needs aggressive treatment.

"In the future, we may be able to determine the amount of lymphatic vessels in a breast cancer specimen obtained from a patient," Detmar said. "And it may potentially allow us to predict whether a tumor has a high risk of metastasis or a low risk depending on the density of lymph vessels in the tissue."

Various proteins are involved in this process -- all in a class called vascular endothelial growth factor (VEGF). VEGF is important in blood vessel formation -- tumors also grow their own little blood supplies -- but it turns out they are involved in lymph vessel growth, too.

In another paper in the same journal, Steven Stacker and colleagues at the Royal Melbourne Hospital in Victoria, Australia, found that, at least in mice, a molecule called VEGF-D caused the formation of both blood and lymph vessels within tumors.

It also led to the spread of cancerous cells to lymph nodes, but could be blocked with an antibody.

And Kari Alitalo and colleagues at the University of Helsinki in Finland, showed a protein called VEGFR-3 can block the actions of both VEGF-C and VEGF-D.

These findings offer possible ways to stop cancer from spreading, the researchers said.