Table of Contents
Cancer: Uncontrolled Cell Proliferation
Cancer is the uncontrolled growth and division (proliferation) of cells. Cells lack the proper mechanisms for APOPTOSIS, the natural process that establishes the end of a cell’s life cycle. In this regard, cancer cells have an endless open throttle: they can divide forever. Cancer cells also lack the proper mechanisms for self-regulation that shut down cell division in abnormal cells; they never stop growing and dividing.
Ordinarily the IMMUNE SYSTEM detects cells that present a threat to the body and mobilizes an IMMUNE RESPONSE to neutralize them before they can do much damage. Cancer cells appear able to evade such detection by the immune system because they arise from cells that belong to the body (self cells).
Even as they mutate cancer cells retain enough essence of their self-cell origin to fool the immune system into continuing to perceive them as self cells. This deception allows cancer cells to congregate, forming the tumors that characterize the disease process of cancer.
Cancer may develop in any cell, with the potential to affect any kind of body tissue. The cells form tumors that invade healthy tissues and can spread to parts of the body beyond the site of origin. Cancer is a threat to health because its presence within tissues and organs disrupts their structure and functions. Tumors take space, NUTRIENTS, and structure that tissues and organs need.
Heredity, Environment, and Aging
Researchers believe cancer is the result of genetic damage within individual cells that allows uncontrolled cell division and growth. This damage may occur as a consequence of heredity or environment or may develop through the process of aging.
Heredity and Cancer
The tendency toward cancer appears to run in families, providing much anecdotal evidence of genetic mutations that contribute to the risk for cancer. Researchers also have isolated specific genes for certain types of cancer, providing objective evidence that cancer can have a hereditary component. When this is the case, a person inherits mutated genes that do not properly regulate specific functions. This lack of regulation results in abnormal cell growth and division that can result in cancer. The BRCA-1/BRCA-2 GENE mutations are among the best known; these mutations are prominent in women who have some types of ovarian or breast cancer. However, only a small percentage of women who have these gene mutations develop cancer, evidence that many factors converge when cancer occurs.
More than a thousand substances found in the environment, natural and synthetic, may cause cancer. Most are chemicals or sources of radiation, both of which alter the molecular structure of cells in ways that change their functions. The most common natural CARCINOGEN is the ultraviolet radiation of sunlight, which is responsible for nearly all SKIN CANCER. Other carcinogens are manmade, notably industrial chemicals such as formaldehyde and vinyl chloride. Many manufacturing processes use these and other carcinogenic chemicals; it is nearly impossible to avoid exposure to them.
Genetic damage to cells may also occur as a consequence of natural deterioration within cells that takes place with aging. Cells become less able to repair themselves and exposure to carcinogens leaves them more vulnerable, allowing errant growth and division. Some cancers that are more common in advanced age are also less harmful to health overall. For example, researchers estimate that 90 percent of men over age 85 have prostate cancer. In most of them the cancer is so slow growing that it does not require treatment.
Traditions in Medical History
Surgery was the first treatment. Even ancient documents record procedures for removal of tumors. However, the development of ANESTHESIA gave surgery its big boost as treatment for cancer, allowing surgeons to more selectively remove tumors. Though the operations were often extensive and traumatic, they were able to save lives.
RADIATION THERAPY was the next treatment developed for cancer. Though doctors began using X-rays on tumors shortly after the discovery of Xrays in the late 19th century, the treatment was often more dangerous than the cancer itself. Radiation burns and radiation sickness were common as doctors struggled to find a balance between enough radiation to kill the tumor and not enough radiation to kill the patient. Finally, in the middle of the 20th century advances in technology and understanding made it possible for radiation to achieve this balance.
For centuries folk medicine contained various substances purported to treat cancer, some of which have become the basis for contemporary CHEMOTHERAPY (such as the camptothecins, vinca alkyloids, and taxanes). During the first half of the 20th century doctors realized that one SIDE EFFECT of poisonous mustard gas, used as a weapon of war, was that it eradicated certain types of cancer. Further exploration resulted in the first class of therapeutic chemotherapy agents, the alkylating agents.
In the later decades of the 20th century, researchers made significant breakthroughs in understanding the functions of the immune system and were able to develop methods to take advantage of the body’s own mechanisms for fighting cancer. IMMUNOTHERAPY is now at the forefront of research.
Breakthrough Research and Treatment Advances
Cancer treatment focuses on removing or disabling affected cells so they can no longer grow and divide. Though cancer remains the second-leading cause of death in the United States, successes in treatments since the 1990s have improved the outlook significantly. Nearly 10 million Americans live with their cancer under control, in REMISSION, or cured. Treatment is so often curative for basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), the two most common types of skin cancer, that cancer statistics do not include these cancers among them.
As researchers learn more about cancer, they are discovering ways to bolster the immune system’s ability to detect and eradicate affected cells before they gain enough momentum to establish themselves as tumors. Cancer vaccines currently in investigational trials show great promise for preventing the development of cervical/prostate cancer, and lymphoma, and for preventing the RECURRENCE of other types cancer. New treatments specifically target molecular functions, either in cancer cells or within the immune response.
These therapies reduce the unpleasant side effects traditionally characteristic of cancer treatment as well as improve the ability to eradicate the cancer. Other therapies establish boundaries around the cancer, containing it so it cannot spread and interfere with structures and functions. Many types of cancer may soon be as manageable (and perhaps preventable) through therapeutic interventions and lifestyle modifications as other chronic health conditions such as CARDIOVASCULAR DISEASE (CVD) and DIABETES.