February 2, 2001

For the first time, researchers at the MGH have identified a new way in which breast cancer cells metastasize to the lymph nodes and lungs. This discovery could lead to new methods to predict and prevent the spread of cancer cells from a primary tumor, believe the researchers. The report from the MGH Cutaneous Biology Research Center (CBRC) appears in the February issue of Nature Medicine.

"We have identified a mechanism of breast cancer metastasis. I wouldn't say it's the only mechanism because there may be several others," says Michael Detmar, MD, (right) a dermatologist and principal investigator in the CBRC. "But this certainly is a major molecular mechanism of how breast cancer metastasizes to the lymph nodes."

Although cancer cells are believed to enter the lymph nodes through the lymphatic system — a multipurpose tangle of vessels — little is known about how tumor cells get from the primary tumor into the lymphatic system. Detmar, Mihaela Skobe, PhD, and their colleagues report that the tumor cells appear to be exiting the tumor through a home-grown system of lymphatic vessels — one expressly cultivated by the tumor.

What is surprising about the discovery is that lymphatic vessels were not previously thought to exist in tumors. Part of the problem, says Detmar, is that until recently there has been no effective means of visualizing lymphatic vessels.

Using a new method for imaging lymphatic vessels, he and Skobe observed networks of the vessels deep inside breast tumor masses grown in mice. The vessels appeared to be carrying tumor cells. Most striking, the number of lymphatic vessels inside the tumor appeared to be correlated with the number of metastatic cells in the lymph nodes and lungs, suggesting that the lymphatic vessels were providing a conduit for the flow of metastatic tumor cells.

This grim realization, if also true in humans, could be turned to a cancer patient's benefit, says Detmar. "In the future, we may be able to determine the amount of lymphatic vessels in a breast cancer specimen obtained from a patient," he says. "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."

Scientists have known for some time that to grow, tumors must induce the growth of new blood vessels, a process called angiogenesis. While lymphatic vessels have been observed to grow and function on the outskirts of a tumor, no one has ever observed them doing so inside a tumor.