Cancer is a condition caused by the uncontrolled growth of cells. Different kinds of cancer are named according to the type of cell that is growing in an uncontrolled way. Cancer can arise from nearly any part of the body. There are more than 125 different types of cancer.
Normal cells grow, divide, and die in a controlled way and with a predictable lifespan. In adults, most cells divide only to replace old cells or to repair damage. Cancer cells have been damaged in such a way that they have lost their normal control mechanisms. They grow and divide at a rapid rate, and outlive their normal lifespan.
Most types of cancer lead to the formation of tumors, abnormal clusters of cells. However, not all tumors are cancerous. Tumors that cannot invade neighboring tissues or spread to other parts of the body are called benign tumors. With rare exceptions, benign tumors do not cause serious disease and are not life threatening. Malignant tumors are cancerous tumors.
Normal cells grow, divide, and die in a controlled way and with a predictable lifespan. In adults, most cells divide only to replace old cells or to repair damage. Cancer cells have been damaged in such a way that they have lost their normal control mechanisms. They grow and divide at a rapid rate, and outlive their normal lifespan.
Most types of cancer lead to the formation of tumors, abnormal clusters of cells. However, not all tumors are cancerous. Tumors that cannot invade neighboring tissues or spread to other parts of the body are called benign tumors. With rare exceptions, benign tumors do not cause serious disease and are not life threatening. Malignant tumors are cancerous tumors.
Malignant tumors can invade and destroy neighboring tissues and organs, and spread to other parts of the body. This spread of cancer cells from one part of the body to another distant site is called metastasis. In short, malignant tumors are capable of invasion and metastasis, but benign tumors do not have these capabilities.
WHAT CAUSES CANCER?
Cancer cells are abnormal because they contain damaged genetic material. The genetic material of human cells is contained in 23 pairs of chromosomes (see Figure 1). Chromosomes are tiny structures inside cells that are made up of a substance called deoxyribonucleic acid or DNA. The DNA inside each cell of your body contains your unique genetic blueprint. Every cell of a person’s body contains an identical copy of his or her unique DNA.
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| Figure 1: Chromosomes and DNA in a Human Cell |
Specific segments of DNA are called genes. Every chromosome contains thousands of genes, each containing the message or genetic code for a specific feature or function of the body.
Genes control every aspect of the body’s structure and function. They control physical features such as height, hair color, eye color, and bone structure. Characteristics such as natural athletic or musical capability, tolerance for pain, and susceptibility to certain diseases are also controlled by genes. Cellular functions such as the ability to repair damage, divide when new cells are needed, and even to die in a specific timeframe are all genetically controlled.
Throughout our lifetime, we are exposed to many things that can damage our DNA. Chemicals in the environment such as asbestos, tobacco smoke, radon, air pollution, radiation from the sun and other sources, viruses, and even chemicals from our own bodies can cause genetic damage. Our bodies have mechanisms to repair genetic damage. Cancer occurs when genetic damage either overwhelms or slips past the body’s normal repair mechanisms. Generally, it takes several different genetic flaws accumulated over a long period of time for a cell to become cancerous.
The abnormalities that lead to cancer are in the genes that control a cell’s life cycle. These genes control when a cell divides and dies. Normally, a cell divides only when it gets a genetic message triggering it to do so. Similarly, cells normally die according to a genetically programmed timeframe. When the genes that control cell division and death are damaged, cells divide uncontrollably and do not die in the normal timeframe. As a result, cancerous cells accumulate in the body forming tumors that eventually crowd out normal cells. Cancer cells do not perform the necessary jobs that normal cells do. Therefore, as cancer cells crowd out normal cells, body functions begin to fail.
The abnormalities that lead to cancer are in the genes that control a cell’s life cycle. These genes control when a cell divides and dies. Normally, a cell divides only when it gets a genetic message triggering it to do so. Similarly, cells normally die according to a genetically programmed timeframe. When the genes that control cell division and death are damaged, cells divide uncontrollably and do not die in the normal timeframe. As a result, cancerous cells accumulate in the body forming tumors that eventually crowd out normal cells. Cancer cells do not perform the necessary jobs that normal cells do. Therefore, as cancer cells crowd out normal cells, body functions begin to fail.
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