Cancer is when abnormal cells divide in an uncontrolled way. Some cancers may eventually spread into other tissues. There are more than 200 different types of cancer. 1 in 2 people in the UK will get cancer in their lifetime but many people are cured. All cancers begin in cells. Our bodies are made up of more than a hundred trillion cells. Cancer starts with changes in one cell or a small group of cells. Usually we have just  the right number of each type of cell. This is because cells produce signals to control how much and how often the cells divide. If any of these signals are faulty or missing, cells may start to grow and multiply too much and form a lump called a tumour. Some types of cancer, called leukaemia, start from blood cells. They don't form solid tumours. Instead, the cancer cells build up in the blood and sometimes in the bone marrow. For cancer to start, certain changes take place within the genes of a cell or a group of cells.


Cancer cells are contained within the body tissues from which they have developed, for example, the lining of the bladder or the breast ducts. Doctors call this superficial cancer growth. It may also be called carcinoma in situ. The cancer cells grow and divide to create more cells grow and divide to create more cells and will eventually form a tumour. A tumour may contain millions of cells. All body tissues have a layer keeping the cells of that tissue inside called the basement membrane. Once the cancer cells have broken through the basement membrane it is called an invasive cancer. A tumour may contain millions of cells.


All body tissues have a layer keeping the cells of that tissue inside called the basement membrane. Once the cancer cells have broken through the basement membrane it is called an invasive cancer. Like healthy cells, cancer cells cannot live without oxygen and nutrients. So they send out signals, called angiogenic factors, that encourage new blood vessels to grow into the tumour. This is called angiogenesis. Without a blood supply, a tumour can't grow much bigger than a pin head. Once a cancer can stimulate blood vessel growth, it can grow bigger and grow more quickly. It will stimulate the growth of hundreds of new capillaries from the nearby blood vessels to bring it nutrients and oxygen.


A lot of research is going on into angiogenesis. The research has found that the amount of angiogenic factors is very high at the outer edges of a cancer. Drugs that stop blood vessel growth (anti angiogenic drugs) can stop a cancer from growing into surrounding tissue or spreading. They can't usually get rid of a cancer completely, but may be able to shrink it or stop it growing in some cases. Some anti angiogenic drugs can control certain types of cancer. More of these drugs are being developed and tested all the time.  As a tumour gets bigger, it takes up more room in the body. The cancer can then cause pressure on surrounding structures.


It can also grow directly into body structures nearby. This is called local invasion. How a cancer actually grows into surrounding normal body tissues is not fully understood. A cancer may just grow out in a random direction from the place where it started. However, tumours can spread into some tissues more easily than others. For example, large blood vessels that have very strong walls and dense tissues such as cartilage are hard for tumours to grow into. So locally, tumours may grow along the 'path of least resistance'. This means that they probably just take the easiest route. Research has pointed to 3 different ways that tumours may grow into surrounding tissues and they are outlined here. A particular tumour will probably use all 3 of these ways of spreading. Which way is used most will depend partly on the type of tumour, and partly on where in the body it is growing.



As the tumour grows and takes up more space, it begins to press on the normal body tissue nearby. The tumour growth will force itself through the normal tissue, as in the diagram below. The finger like appearance of the growth happens because it is easier for the growing cancer to force its way through some paths than others. For example, cancers may grow between sheets of muscle tissue rather than straight through one particular muscle. As the cancer grows, it will squeeze and block small blood vessels in the area. Due to low blood and oxygen levels, some of the normal tissue will begin to die off. This makes it easier for the cancer to continue to push its way through.



Copyright © 2017 Science Union, Vembadi Girls' High School. All Rights Reserved.