Cancer is a term that defines a collection of diseases that can affect almost every part of the body. There are more than 200 different types of cancer. The common defining feature of the disease is the rapid creation of abnormal cells that grow beyond their usual boundaries. More specifically, the genetic material of a cell has acquired mutations, causing abnormal cell production. The extra cells may form a mass of tissue called a tumor. A tumor can be benign, pre-malignant, or malignant. A benign tumor typically does not grow in an aggressive manner, does not invade surrounding tissue, and does not metastasize or spread to other nearby tissue or organs. A malignant tumor, by contrast, is not self-limited in its growth and may spread to other parts of the body. A pre-malignant tumor is a tumor that may lead to cancer if left untreated.
There are five broad types of cancer:
- Carcinomas - cancers that begin in the skin or tissues that line internal organs;
- Sarcomas - cancers that originate in the bone, cartilage, fat, muscle, blood vessels, or other connective tissues;
- Leukemias - cancers that originate in blood-forming tissue, such as bone marrow, and cause a large quantity of abnormal blood cells to be produced;
- Lymphoma and myeloma - cancers that begin in the immune system; and
- Central nervous system cancers - cancers that begin in the tissue of the brain and spinal cord.
Cancer cells can travel to other parts of the body through the bloodstream, where they begin to grow and form new tumors that replace normal tissues. This process is known as metastasis. Cancer is always named for the place it originated. Different types of cancer behave differently, grow at different rates, and respond to different treatments. For this reason, individuals diagnosed with cancer should consult a doctor to begin a treatment program targeted towards their particular kind of cancer.