This could provide a new target for therapy

Dr Michael Detmar, Massachusetts General Hospital

Although the route to the lymph nodes is clear once the cells have managed to enter the tiny network of vessels in the lymphatic system, how the cells jump over into the lymphatic system has until now been a mystery.

Doctors believe that they now may even be able to block this spreading process, called metastasis, improving the chances of thousands of breast cancer patients.

It has long been known that some tumours are able to flourish by growing their own supply network of blood vessels.

However, the new study suggests that the tumour cells are leaving the tumour mass by their own home-grown lymphatic vessels.

A research team looked closely at breast tumours grown in mice, and found that the mass had its own network of lymphatic-like vessels, which also appeared to be carrying tumour cells.

Measuring the risk

The number of these vessels correlated strongly with the number of metastatic cells in the lymph nodes and lungs.

Dr Michael Detmar, from the Massachussetts General Hospital Cutaneous Biology Research Center, said that measuring the number of these vessels in human tumours could help doctors predict the likelihood of spread outside the breast.

He said: "We have identified a mechanism of breast cancer metastasis. This is certainly a major molecular mechanism of how breast cancer metastasizes to the lymph nodes."

Another experiment saw some mice implanted with tumour cells which were genetically modified to experience boosted lymphatic growth.

The research team found that not only did the lymphatic vessels spring up inside the tumour, but they also appeared to even hook up with those outside the tumour - creating a ready-made highway to carry cancer cells to other parts of the body.

Blocking similar genes in human tumours, Dr Detmar said, could help prevent or at least reduce the likelihood of metastasis.

"This could provide a new target for therapy," he said.