Cancer is the generic name for a range of more than 200 diseases characterized by uncontrolled cell growth in a part of the body. After cardiovascular disease, cancer is the most common cause of death in the industrialized world. More than 25 percent of all deaths are due to some type of cancer.
Although progress is being made in the treatment of cancer, total mortality is increasing year on year. This is mainly due to an ageing population. Half of all men and a third of all women will develop cancer during their lifetime (source: American Cancer Society, National Cancer Institute). The most common reasons for death from cancer include the development of resistance to the prevailing treatment and the development of metastases (satellites of the primary tumor that have spread in the body). This means that with today’s therapies – which are often initially successful – the disease can recur, and is then often more resistant to therapy. Around 10% of all cancers are due to hereditary factors, while around 90% are due to lifestyle. By stopping smoking, limiting time spent in the sun, being physically active and eating healthily we can reduce our risk of developing cancer. However, the causes of many cases of cancer remain unclear. Increased understanding of both the underlying causes of cancer and what makes cancer cells resistant to current therapies is expected to result in more effective treatments and more sensitive diagnostics. Improved diagnostics will enable cancer to be discovered at an early stage and to know what treatment is most appropriate, which in turn results in better opportunities to cure the disease or keep it under control for many years.
The body is made up of around 100,000 billion cells that normally grow, divide and die in a controlled way, allowing a healthy life. A child’s cells divide at a faster rate to allow growth. Once the child is fully grown, most cell division takes place to replace damaged and aged cells. Cancer starts when cells in a part of the body begin to grow in an uncontrolled manner. Cancer cells are characterized primarily by the fact that they stimulate themselves to grow, they do not die despite their genome being damaged, they can divide almost infinitely, they are able to send out metastases to other parts of the body, and they spread so that the surrounding tissue is affected by being supplanted or invaded. The characteristics that make a cell into a cancer cell are directly or indirectly linked to a change in or damage to the genome (DNA). When DNA is damaged in a normal cell, then either the DNA is repaired or the cell dies. The cancer cell, however, lives on despite DNA damage that gives it its capacity to grow and avoid cell death. Instead it continues to form new cells – cells that will have the same damage to the DNA as the original cancer cell.
People can inherit damaged DNA, but most DNA damage found in cancer arises by mistake when a normal cell divides or is exposed to something harmful in the environment. Sometimes we can understand the cause of the DNA damage, such as with smoking, but often the reason is difficult to trace. In most cases cancer forms a tumor, but there are exceptions such as leukemia. In leukemia new cancer cells are formed in bone marrow. From the bone marrow these cells go out into the blood, where they circulate through tissues where they continue to divide. Irrespective of which organ a cancer spreads to, it is named according to where it started. If bowel cancer has spread to the liver then it is metastatic bowel cancer, not liver cancer. Different types of cancer are sensitive to different types of treatment. Metastases from lung cancer and from breast cancer behave very differently, for example. They grow at different rates and are sensitive to different drugs. This is why it is important to understand the origin of the patient’s cancer.