Tumors can grow to a very surprising size if left untreated. The largest tumor ever removed in recent medical history was a 110 Kg neurofibromatosis, which was operated on in a hospital in Beijing. A medium-sized female adult weighs around 70 Kg. In order for all the cells in the medium-sized adult female to stay alive, her body would need a complex network of blood vessels (veins, arteries and capillaries) and a healthy heart to pump blood through it. The blood would rush through the body, carrying oxygen and nutrients an taking away the CO2 and waste products the cells have produced. Without some type of cardiovascular system (that is the combination of blood vessels and a heart), no large group of animal cells can survive. It makes sense then that a large lump of cancer cells would not be able to survive without its own suppl of food and oxygen from the cardiovascular system.
The trouble is, tumors are not connected to the main blood vessel network as they are rogue lumps of cells reproducing out-of-control. In a way, tumors are a lot like homes built without planning permission: they are not connected to the “mains” and therefore need to find a way to illegally connect to them in order to have access to electricity, drinking water and sewage. In a similar way, tumors have to grow their own blood vessels in order to be able to survive and grow. This process is known as angiogenesis. Angiogenesis comes from the Ancient Greek and literally means “creating blood vessels”. The way cancer cells achieve this is by manipulating the molecular network that is in place for the regular formation of blood vessels. Blood vessels usually form when the body grows to account for the increased demand in oxygen and nutrients. They form in response to very specific chemical signals that are released by growing cells. Cancer cells have found a way to produce the same signals, which trick the body into knitting new blood vessels to sustain the growing tumor. This is a really common mechanism, where cancer cells hijack biochemical mechanisms used by healthy cells. It makes developing drugs against these steps especially difficult, as any drug stopping the cancer-driven process would also stop the healthy mechanism needed by the body to stay alive. However, cancer science is making giant leaps in making better and better drugs targeting only the cancerous chemical processes. Drugs stopping angiogenesis are being developed and used to help patients with many different types of cancer and constitute a real hope for the cancer patients of the future.
A chilling side-note is that angiogenesis serves a dual purpose, allowing both nutrients to reach cancer cells and cancer cells to escape their original niche. In fact, cancer cells usually find a way to crawl into the blood vessels they have helped to form. They use the blood flow as a way to spread throughout the body, where they form secondary tumors, also known as metastases.
This post is within the series “Understanding Cancer”. Please check out the rest of the posts here.