How Cancer Works in the Body
Characteristics of Cancer Cells
Cancer begins when healthy cells lose their natural ability to regulate their own growth. Six characteristics define cancer cells: the ability to bypass normal growth cycles, insensitivity to natural signals regulating cell growth and division, lack of the mechanism initiating natural cell death, no mechanism regulating cell division, the ability to construct their own blood supply and the ability to invade neighboring tissues and spread (metastasize) to other organs. In short, tumors consist of normal cells that have been damaged and grow too quickly, reproduce too frequently, live too long and migrate throughout the body. As the cancerous cell continues to grow and multiply without a need to replace dying cells, the excess cells accumulate and eventually form a mass, or tumor. Tumors are either benign, which means they are not cancerous and pose no threat to neighboring tissues, or malignant, which means the tumor is cancerous and will continue to grow and invade other organs. Cancers such as leukemia and lymphoma, however, do not form tumors. Cancer is not a single disease. Each type of cancer has its own characteristics with different growth patterns, levels of aggressiveness and treatments.
What Causes Cells to Become Cancerous
Cells naturally follow a cycle in which they grow, divide and die according to chemical signals. Sometimes the DNA of a cell becomes damaged by infection with certain viruses or bacteria, exposure to radiation or chemicals, heredity or aging. Cells have a natural mechanism to correct damaged DNA before the cell divides and replicates the flaw. In most cases, the mutation is harmless. However, in some instances, the cell fails to correct the flaw and the mutation leads to the uncontrolled growth of cancer. Researchers have not discovered why some cells become cancerous and others do not, or what exactly causes a cell to become cancerous. It is certain that cancer results from many mutations over time rather than a single defect. Heredity plays a role, leaving some people susceptible to certain types of cancers, such as breast cancer. Other types of cancers are linked to diet, such as colon cancer, or behaviors, such as lung cancer. Aging is a risk factor because small mutations build over time. The presence or absence of specific genes called oncogenes also prompt cancer development. Oncogenes code for proteins that regulate cell growth and stimulate apoptosis, therefore cells lacking these proteins grow without natural restrictions.
Metastasis
Metastasis, or the ability of cancer to spread to organs distant from the original tumor site, is the hallmark characteristic of cancer cells. Local metastasis occurs when the cancer cells invade neighboring tissue while distant metastasis is when the cancer spreads to an organ away from the original tumor, such as prostate cancer spreading to the liver. Healthy cells stop growing when they encounter neighboring cells. Cancerous cells, however, lack this ability. The force of the growing tumor coupled with the excess production of enzymes that break down cells and tissues allows the tumor to create the space it needs to continue growing. Another distinguishing characteristic of cancer cells is their ability to migrate easily. Cancer cells break off from the original tumor and enter the bloodstream or lymphatic system, which carries them throughout the body.
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