The National Cancer Institute states there are more than 100 different diseases that fall under the category of cancer. Although cancers differ by the site of the body in which they originate and other factors, cancer cells of all types share certain characteristics.
Uncontrolled Proliferation
Normal cells divide and create new cells only when they are needed. One of the hallmark characteristics of cancer cells is their loss of controlled proliferation. Cancer cells' uncontrolled proliferation is one of their most destructive characteristics.
Invasiveness
Another hallmark characteristic of cancer cells, which distinguishes them from normal cells, is their propensity to invade. Cancer cells can invade nearby tissues and organs (local invasion) or they may spread to other areas of the body by a process called metastasis. Different types of cancer have different invasive affinities. Some are prone to local invasion, whereas others commonly metastasize to distant organs.
Cancer cells' invasiveness combined with their uncontrolled proliferation can create a lethal situation for the body's normal tissues. As the number of cancer cells increases and they begin to invade, normal cells are overtaken. Think of the cancer cells' takeover as being akin to what happens when your lawn becomes infested with weeds. Imagine the weeds are cancer cells and the grass represents normal cells. The weeds multiply and grow faster than the grass, encroaching on the space where the grass lives. Unless you do something to get rid of the weeds, they will take over, leaving no room for the grass. An analogous situation occurs in the body as normal cells and cancer cells compete for survival. Cancer cells' uncontrolled proliferation and invasiveness give them the upper hand.
Loss of Programmed Cell Death
Normal cells have a finite lifespan, a feature called programmed cell death. Cells normally come into existence, do their job, and then die--but the same is not true of cancer cells. Cancer cells do not have a fixed lifespan. As long as they are able get the nutrients needed to survive, cancer cells are essentially immortal. They will continue to live and divide at an uncontrolled pace unless something happens to stop them.
Genetic Abnormalities
All cancer cells have abnormalities in their genetic material. The genetic material of a cell--its DNA--is the master controller of the cell's structure and activities. Cancer cells have many genetic abnormalities, not just a single bad gene. Each of the abnormal characteristics of cancer cells is due to one or more genetic mutations.
Some genetic mutations that contribute to a person's susceptibility to cancer are inherited. The BRCA genes associated with breast and ovarian cancers are one such example. However, only 5 to 10 percent of cancers are believed to occur in the setting of an inherited genetic mutation. Most cancerous mutations occur during the course of a person's life. Environmental factors, personal habits and your immunologic makeup can affect your predisposition to cancer by influencing the likelihood of genetic mutations and your body's ability to repair or eliminate them when they occur.
Evasion of Immune System Surveillance
In the normal course of events, human cells experience mutations. Fortunately, the body has elaborate mechanisms to deal with this problem. Cells can scan for and sometimes repair genetic mishaps, or a mutation may trigger the programmed death of a cell. If a mutation is not repaired and the cell does not die, there is a second line of defense.
The immune system has specialized cells that conduct surveillance, looking for genetically damaged cells. The immune system destroys the defective cells when they are found. Malignant cells that cause cancer all have the ability to evade the body's cancer surveillance system.
Abnormal Function
Some of the genetic defects of cancer cells result in loss of normal function. Therefore, cancer cells typically fail to perform many or all of the usual functions of the cells from which they arose. As cancer cells proliferate and take over healthy tissue, normal function of the affected organ is often compromised.
References
- National Cancer Institute: What Is cancer?
- American Cancer Society: What Is cancer?
- "Clinical Oncology, Third Edition;" Martin D. Abeloff, M.D. et.al., Editors; 2004
- National Cancer Institute: BRCA1 and BRCA2: cancer risk and genetic testing
- "Journal of Clinical Oncology;" Hereditary cancer predisposition syndromes; Judy E. Garber, M.D., M.P.H., Kenneth Offit, M.D., M.P.H.; January 2005
