Cancer Health Article

Definition

Cancer is not just one disease, but a large group of diseases characterized by uncontrolled and abnormal growth of the cells in the human body and the ability of these cells to spread to distant sites (metastasis). If the spread is not controlled, cancer can result in death.

Description

Cancer, by definition, is a disease of the genes. Genes are formed from deoxyribonucleic acid (DNA) and located on chromosomes. They carry the hereditary instructions for the cell to make the proteins required for many body functions. Proteins are special chemical compounds that mostly contain carbon, hydrogen, oxygen, and nitrogen and that are required by our bodies to carry out all the processes that allow us to breathe, think, move, etc.

Throughout people's lives, the cells in their bodies are growing, dividing, and replacing themselves. Many genes produce proteins that are involved in controlling the processes of cell growth and division. A change (mutation) occurring in the DNA molecules can disrupt the genes and produce faulty proteins and cells. Abnormal cells can start dividing uncontrollably, eventually forming a new growth known as a "tumor" or "neoplasm" (medical term for cancer meaning "new growth"). In a healthy individual, the immune system can recognize the neoplastic cells and destroy them before they get a chance to divide. However, some abnormal cells may escape immune detection and survive to become cancerous.

Tumors are of two types, benign or malignant. A benign tumor is slow growing and does not spread or invade surrounding tissue. Once the tumor is removed, it will not usually start growing again. A malignant tumor, on the other hand, invades surrounding tissue and can spread to other parts of the body, often very distant from the location of the first tumor. Malignant tumors can be removed, but if the cancer cells have spread too much, the cancer becomes very difficult, if not impossible, to treat.

Most cancers are caused by changes in the cell's DNA that result from exposure to a harmful environment. Environmental factors responsible for causing the initial mutation in the DNA are called carcinogens. Other factors can cause cancer as well. For example, certain hormones have been shown to have an effect on the growth or control of a particular cell line. Hormones are substances made by one organ and passed through the bloodstream to affect the function of other cells in another organ.

While there is scientific evidence that both environmental and genetic factors play a role in most cancers, only 5-10% of all cancers are classified as hereditary. This means that a faulty gene that may cause cancer is passed from parent to child. This results in a greater risk for that type of cancer in the offspring of the family. However, if someone has a cancer-causing gene, this doesn't mean they will automatically get cancer. Rather, this person is thought to be "predisposed" to a type of cancer, or more likely to get this cancer when compared to the general population. Various cancers are known to have a hereditary component in some cases. A few examples are breast cancer, colon cancer, ovarian cancer, skin cancer and prostate cancer.

Aside from genes, certain physiological traits that are inherited can contribute to cancers as well. For example, fair skin makes a person more likely to develop skin cancer, but only if they also have prolonged exposure to intensive sunlight.

There are several different types of cancers. Some of the most common types include:

• Carcinomas These cancers arise in the epithelium (the layers of cells covering the body's surface and lining the internal organs and various glands). About 80% of human cancers fall into this category. Carcinomas can be subdivided into two subtypes: adenocarcinomas and squamous cell carcinomas. Adenocarcinomas are cancers that develop in an organ or a gland, while squamous cell carcinomas refer to cancers that originate in the skin.
• Melanomas This form also originates in the skin, usually in the pigment cells (melanocytes).
• Sarcomas These are cancers of the supporting tissues of the body, such as bone, muscle, cartilage, and fat.
• Leukemias Cancers of the blood or blood-forming organs.
• Lymphomas This type affects the lymphatic system, a network of vessels and nodes that acts as a filter in the body. It distributes nutrients to blood and tissue and prevents bacteria and other foreign substances from entering the bloodstream.
• Gliomas Cancers of the nerve tissue.

The most common cancers are skin cancer, lung cancer, colon and rectal (colorectal) cancer, breast cancer (in women), and prostate cancer (in men). In addition, cancer of the kidneys, ovaries, uterus, pancreas, bladder, and blood and lymph node cancer (leukemias and lymphomas) are also included among the 12 major cancers that affect most Americans.