Cancer, also called malignancy or neoplasm, develops when cells in a specific part of the body begin to grow out of control. Unlike normal cells, cancer cells do not stop reproducing after they have doubled 50-60 times.
Normal body cells grow, divide, and die in an orderly, natural fashion. Normal cells divide more rapidly during the early years of an individual's life. After adulthood is reached, cells in most parts of the body divide only to replace worn-out or dying cells and to repair injuries. Cancer cells continue to grow and divide, forming new abnormal cells.
Cancer cells usually form a tumor. Some cancers, such as leukemia or cancer of the bone marrow and blood, do not form tumors. Instead, these cancer cells circulate through other tissues, where they grow.
Not all tumors are cancerous. Benign (noncancerous) tumors do not metastasize (spread) to other parts of the body and, with very rare exceptions, are not life threatening. Different types of cancer can grow at different rates and respond to different treatments. Malignant, or cancerous, tumors may metastasize and cause further damage to organs and tissues in the body.
Cancer cells develop because of damage to DNA (the material inside the nucleus of a cell that carries genetic information). DNA occurs in most cells of the body and is the blueprint for how the body grows, functions, and stays healthy. Usually, when DNA becomes damaged, the body is able to repair it. In cancer cells, the damaged DNA is not able to be repaired. Individuals can inherit damaged DNA, such as with inherited cancers. More often, though, an individual's DNA becomes damaged by exposure to something in the environment, such as smoking or radiation from the sun.
The immune system, which is made up of special cells, proteins, tissues, and organs, defends individuals against invasion by pathogens (disease-causing agents), such as cancer cells, bacteria, and viruses. The differences between cancer cells and normal cells may not be easily detected, and the immune system may not always recognize cancer cells as pathogens. Most healthy individuals have immune systems that can keep up with the pathogens, but sometimes problems with the immune system can lead to illness and infection.
Cancer cells sometimes travel through the blood or lymphatic system to other parts of the body. The cancerous cells begin to grow and replace normal tissue in a process called metastasis. Regardless of where cancer may spread, it is always named for the place it began. For instance, colon cancer that spreads to the liver is still called colon cancer, not liver cancer.
Symptoms and treatment depend on the cancer type and how advanced it is. Treatment plans may include surgery, radiation, and/or chemotherapy. The most common cancers are breast cancer, lung cancer, bowel or colon cancer, prostate cancer, bladder cancer, non-Hodgkin's lymphoma, stomach cancer, melanoma, esophageal cancer, pancreatic cancer, leukemia, and ovarian cancer.
According to the American Cancer Society (ACS), cancer is the leading cause of death among Americans under the age of 85. Half of all men and one-third of all women in the United States will develop cancer during their lifetimes. Although cancer occurs in Americans of all racial and ethnic groups, the rate of cancer occurrence varies from group to group. Two-thirds of individuals diagnosed with cancer are aged over 65 years. In 2005, 7.6 million people died of cancer, out of 58 million deaths worldwide. Based on projections, cancer deaths will continue to rise, and an estimated nine million people will die from cancer in 2015, and 11.4 million may die in 2030.
Early diagnosis makes it more likely that cancer can be treated successfully. It is important that individuals are aware of possible symptoms and that individuals see a doctor for regular checkups.

Related Terms

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types of cancer

There are over one hundred types of cancer that can affect the human body. Each of the types of cancer has its own name, behavior, and course of treatment. All cancers involve the abnormal growth of cells. The most commonly found cancers in humans include carcinoma, sarcoma, leukemia, lymphoma, and adenoma.
Carcinoma: More than 85% of cancers are carcinomas. Carcinomas start in the cells that line and cover internal and external organs. The most common carcinomas are lung cancer, breast cancer, skin cancer, and bowel cancer.
Sarcoma: Sarcoma begins in supportive tissues of the body, such as muscle, bone, cartilage, blood vessels, fat, and connective tissue.
Leukemia: Leukemia is cancer of the blood cells that grows in the bone marrow.
Lymphoma: Lymphomas develop in the lymph nodes and tissues of the immune system.
Adenoma: An adenoma is a tumor (usually benign) that begins in glandular tissue, such as the adrenal, pituitary, or thyroid gland.