Cancer is a group of about 100 diseases involving abnormal cell growth. Although most individuals facing a cancer diagnosis want to know what caused their cancer, the answer is not that simple.\nLiving organisms, including human beings, are made up of cells. Cells generally have a specific life cycle depending on their location in the body. Different cells have different lifespans.\nFor instance, your liver cells may live from six months to a year before being replaced. Taste buds have it rough; they are replaced every 10 to 14 days. Healthy cells have the ability to self-destruct when they die or become damaged. Normal, healthy cells also grow and divide in a controlled fashion. When a healthy cell dies, in general, it is replaced by another healthy cell. Changes in a healthy cell can cause it to grow in an uncontrolled fashion, resulting in a tumor or mass.\nRelated: The Value of Taking Part in a Clinical Trial\nMajor Differences Between Cancer Cells and Normal Cells\nCancer cells vary greatly from normal cells. Learn more about the differences between them.\nGrowth\n\nCancer cells continue to grow after enough cells are present. This overgrowth forms a cluster of cells, causing the formation of a tumor\nNormal cells stop growing when enough cells are present\n\nCommunication\n\nCancer cells do not respond to the signals from other cells warning overgrowth\nNormal cells, in turn, respond to these signals and stop growing\n\nCell Repair\n\nCancer cells don\u2019t repair themselves when they are old or damaged\nNormal cells do repair themselves or may even die off if they are not healthy\n\nThe Lifespan of Cancer Cells\nWhen a cell does not die as expected, it may continue to grow from abnormally produced cells. Cancer cells do not have a regular lifespan like normal cells. They can grow uncontrollably, often spreading to other areas of the body. This spreading is known as metastasis. Although cancer may spread to other organs, it is always named for the organ where it started. For example, breast cancer that has spread to the brain is called metastatic breast cancer. Some cancers do not occur as a mass or tumor but affect the blood and blood-producing organs, such as leukemia.\nNot All Tumors are Cancerous\nIt is normal to be worried about a lump under your skin, but there are many types of tumors that are benign, or not cancerous. While a tumor can cause problems such as growing large and pushing on organs or tissues, it will not spread to the other organs. If you\u2019re concerned about a lump on or under your skin or other unusual symptoms, talk to your doctor.\nFor more information about cancer prevention, check out these 5 Ways to Help Prevent Cancer.