Cancer is a serious disease that can develop from different types of cells and affect many parts of the body. It causes symptoms such as pain, fatigue and bleeding from tumors, and sometimes makes it hard for the body to work correctly. Many times cancer can be found and treated when it is caught early. But, there are also times when it may not be able to be treated and the patient will die from the disease.

For centuries, doctors and scientists have been trying to understand what causes cancer and how it can be prevented or cured. With the help of many important discoveries in science and medicine, we now know a great deal about how cancer forms, grows and spreads.

When a normal cell becomes cancerous, it divides more than it should and produces a population of abnormal cells known as a tumor. These cells can grow and invade nearby tissue and can be a source of cancer spreading to other areas of the body.

Until recently, scientists believed that all cancers begin in one normal cell and then spread to the tissues around it by a process called metastasis. This theory has been largely disproved and researchers now believe that most cancers start in cells that are unable to control their growth or stop dividing when they should. These abnormal cells can then break away from the original tumor and travel through the blood or lymph system to other parts of the body where they may form new tumors or cause existing tumors to grow and spread.

These cancer-causing mutations can occur in genes that manage how cells work, or in the signals that tell cells when to start or stop dividing. Some of these changes are inherited, but others can be acquired during life as a result of habits such as smoking or exposure to sunlight. Scientists are now beginning to understand how these genetic and environmental factors combine to create a cancer that, once it starts, is very difficult to cure.

Because the growth and spread of cancer is a step-by-step process that takes place over long periods of time, it is easy to miss early warning signs of the disease. Sometimes the disease is not obvious because the symptoms are mild or because it has only just begun to grow and spread. That is why it is important for people to let their healthcare providers know if they have any changes in their bodies that last more than two weeks.

There are many kinds of cancer and each type can be treated differently. Treatment may slow the cancer’s growth, ease symptoms and improve a person’s quality of life. The type of cancer, its stage (how far it has spread) and a person’s general health will determine what kind of treatment is most effective. For example, some cancers are more likely to stay in one part of the body (localized) and respond well to surgery or radiation treatments while others can spread quickly and require chemotherapy to kill fast-growing cancer cells.