The Immune System and Cancer – New Insights into a Not Always Healthy Interplay

At the International conference “Invasion and Metastasis” held at the Max Delbrück Center for Molecular Medicine (MDC) in Berlin, Dr. David DeNardo from the laboratory of Professor Lisa Coussens from the University of California, San Francisco, USA reported on how tumours use immune cells to grow faster and disseminate in the body.

When germs infiltrate a wound after injury, the body can well defend itself. Immune cells recognize the pathogens and initiate inflammation to limit infection. Attracted by this warning, many different cells of the immune system migrate to the centre of inflammation to help fight off the intruders. The injured area gets hot and red and becomes more sensitive and swollen. When the healing process is completed, inflammation abates and the immune cells withdraw. When some types of immune cells encounter tumour cells, they can also cause inflammation. Compared to normal injury, however, these immune cells often do not withdraw, but rather generate an enduring, chronic inflammation. “Therefore, we call tumours wounds that never heal,” Dr. DeNardo illustrated.

During the healing process, the immune cells attracted to a wound not only combat the invaders, but also produce growth factors and so-called proteases, enzymes that remodel the connective structures between cells. In addition, new blood vessels are formed to provide the injured tissue with oxygen and nutrients. This formation of new blood vessels is known as angiogenesis. „Normally these mechanisms enhance sealing of the wound,” Dr. DeNardo said. “However, cancer cells exploit them for their own interests.”

Growth factors permit tumour cells to continue proliferating when proteases remodel the connective structures between cells and thus enable single cancer cells to disseminate from the original tumour. However, angiogenesis also helps metastases, the dangerous daughters of a primary tumour, to form. The new blood vessels grant single disseminated cancer cells access to the bloodstream much faster.

“Scientists are trying to develop strategies to stop these processes of inflammation and this way,” Dr. DeNardo hopes, “help cancer patients.” It has already been shown that some cancer metastases develop more rarely in patients who regularly take acetylsalicylic acid. This substance inhibits inflammation and thus blocks the processes cancer uses to grow and spread.