There are more than 100 diseases that fall under the broad umbrella of “cancer.” The uniting feature of these diseases is abnormal cell division — cancerous cells are those that grow out of control. Though cell division is an important bodily process that allows for growth and repairing injuries, when the DNA safeguards that control division rates fail, cancer develops. These cancerous cells often invade other, healthy tissues, something normal cells cannot do.
Damage to a cell’s DNA may cause it to replicate instead of die when it is no longer needed, creating more cells with damaged DNA. A variety of factors can cause this damage, from genetic abnormalities to environmental causes like smoking or asbestos exposure. However, the cause is not always known. If cancerous cells spread to other parts of the body through blood or lymph vessels, the cancer is said to have metastasized. This is often a sign that the cancer is in its later stages and makes the disease more difficult to treat.
Though in common speech, “tumor” is sometimes used as interchangeable with “cancer,” these words refer to two different things; not all cancers cause tumors, and not all tumors are cancerous. Leukemia, for example, causes cancer cells to develop in the blood and blood-forming organs like bone marrow, but does not form tumors. Benign tumors are noncancerous and cannot invade other tissues or metastasize. However, a benign tumor can cause health problems if it continues to grow and presses into other organs, disrupting their function.
Types of Cancer
Cancers can be divided into broad categories based on the locations where they originate. Carcinomas are cancers that begin in the skin or lining of the internal organs, whereas sarcomas are those that start in bone, cartilage, fat, muscle, blood, vessels, or other connective tissue. Leukemia, as noted above, begins in blood-forming tissues, and lymphoma and myeloma are cancers of immune system tissues and organs. Finally, central nervous system cancers are those that develop in the brain or spinal cord.
Unfortunately, cancer has become an extremely common phenomenon. The American Cancer Society projects that one-third of all women and half of all men in the United States will develop cancer at some point during their lifetimes. According to the National Cancer Institute, over 1.5 million new cases of cancer, not including melanoma, were reported in 2010, and 569,490 people died of cancer. Risk factors vary from region to region as well as person to person. Factors known to increase risk of developing cancer include smoking, heavy drinking, exposure to ultraviolet rays and sunlight, and poor diet.