Cancer is an abnormal growth of cells. Cancer cells rapidly reproduce despite restriction of space, nutrients, or signals sent from the body to stop reproduction. Cancer cells are often shaped differently from healthy cells, do not function properly, and can spread to many areas of the body. Tumors, abnormal growths of tissue, are clusters of cells that are capable of growing and dividing uncontrollably; their growth is not regulated.
Oncology is the branch of medicine concerned with the diagnosis and treatment of cancer.
Tumors can be benign (noncancerous) or malignant (cancerous). Benign tumors tend to grow slowly and do not spread. Malignant tumors can grow rapidly, invade and destroy nearby normal tissues, and spread throughout the body.
Cancer is malignant because it can be locally invasive and metastatic.
The original tumor is called the primary tumor. Its cells, which can break off and travel through the body, can begin the formation of new tumors in other organs. These new tumors are referred to as secondary tumors. The cancerous cells travel through the blood - the circulatory system - or lymphatic system to form secondary tumors. The lymphatic system is a series of small vessels that collect waste from cells, carrying it into larger vessels, and finally into lymph nodes. Lymph fluid eventually drains into the bloodstream.
Cancer is named after the part of the body where it originated. When cancer spreads, it keeps this same name. For example, if kidney cancer spreads to the lungs, it is still kidney cancer, not lung cancer. (The cancer in the lung would be an example of a secondary tumor.) Staging is the process of determining whether cancer has spread and, if so, how far. More than one system is used for staging cancer, and the definition of each stage will depend on the type of cancer.
Cancer is not just one disease but rather a group of diseases, all of which cause cells in the body to change and grow out of control. Cancers are classified either according to the kind of fluid or tissue from which they originate, or according to the location in the body where they first developed. In addition, some cancers are of mixed types. The following five broad categories indicate the tissue and blood classifications of cancer:
There is no one single cause for cancer. Scientists believe that it is the interaction of many factors together that produces cancer. The factors involved may be genetic, environmental, or lifestyle characteristics of the individual.
As mentioned, some cancers, particularly in adults, have been associated with certain risk factors. A risk factor is anything that may increase a person's chance of developing a disease. A risk factor does not necessarily cause the disease, but it may make the body less resistant to it. People who have an increased risk of developing cancer can help to protect themselves by scheduling regular screenings and check-ups with their physician and avoiding certain risk factors. Cancer treatment has been proven to be more effective when the cancer is detected early. The following risk factors and mechanisms have been proposed as contributing to the development of cancer:
The discovery of certain types of genes that contribute to cancer has been an extremely important development for cancer research. Virtually all cancers are observed to have some type of genetic alteration. A small percentage - 5 to 10 percent - of these alterations are inherited, while the rest are sporadic, which means they occur by chance or occur from environmental exposures, usually over many years. There are three main types of genes that can affect cell growth, and are altered, or mutated, in certain types of cancers, including:
Usually, the number of cells in any of our body tissues is tightly controlled so that new cells are made for normal growth and development, as well as to replace dying cells. Ultimately, cancer is a loss of this balance due to genetic alterations that "tip the balance" in favor of excessive cell growth.
Diagnosis, treatment, and prognosis for childhood cancers are different than for adult cancers. The main differences are the survival rate and the cause of the cancer. The five year survival rate for childhood cancer is about 80 percent, while in adult cancers the five year survival rate is 68 percent. This difference is thought to be because childhood cancer is more responsive to therapy, and a child can tolerate more aggressive therapy.
Childhood cancers often occur or begin in the stem cells, which are simple cells capable of producing other types of specialized cells that the body needs. A sporadic (occurs by chance) cell change or mutation is usually what causes childhood cancer. In adults, the type of cell that becomes cancerous is usually an epithelial cell, which is one of the cells that line the body cavity, including the surfaces of organs, glands, or body structures, and cover the body surface. Cancer in adults usually occurs from environmental exposures to these cells over time. Adult cancers are sometimes referred to as acquired for this reason.
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