What Is Cancer?
Cancer is a group of diseases characterized by uncontrolled cell division leading to growth of abnormal tissue. It is believed that cancers arise from both genetic and environmental factors that lead to aberrant growth regulation of a stem cell population, or by the dedifferentiation of more mature cell types.
Cell multiplication (proliferation) is a normal physiologic process that occurs in almost all tissues and under many circumstances, such as response to injury, immune responses, or to replace cells that have died or have been shed as a part of their lifecycle (in tissues such as skin or the mucous membranes of the digestive tract).
Normally the balance between proliferation and cell death is tightly regulated to ensure the integrity of organs and tissues. Mutations in DNA that lead to cancer appear to disrupt these orderly processes.
The uncontrolled and often rapid proliferation of cells can lead to either a benign tumor or a malignant tumor (cancer). Benign tumors do not spread to other parts of the body or invade other tissues, and they are rarely a threat to life. Malignant tumors can invade other organs, spread to distant locations (metastasize) and become life threatening.
Cancer is caused by the accumulation of multiple mutations in the DNA of a cell. Once a single cell becomes cancerous it, over time, expands into a large tumor. Mutations can be caused by many different mechanisms, not all are known.
In addition, not all mutations lead to cancer. Hence, the cause for a specific case of cancer cannot usually be identified in the way that the cause of chicken pox can be attributed to transmission of Varicella-zoster virus. Instead, different factors impart a probabilistic risk to developing cancer.
Most forms of cancer are sporadic, and have no basis in heredity. There are, however, a number of recognised syndromes of cancer with a hereditary component. Examples are:
- breast cancer and ovarian cancer in female carriers of BRCA1
- tumors of various endocrine organs in multiple endocrine neoplasia (MEN types 1, 2a, 2b)
- Li-Fraumeni syndrome (various tumors such as osteosarcoma, breast cancer, soft-tissue sarcoma, brain tumors) due to mutations of p53
- Turcot syndrome (brain tumors and colonic polyposis)
- Familial adenomatous polyposis an inherited mutation of the APC gene that leads to early onset of colon carcinoma.
Environment and diet
The incidence of lung cancer is highly correlated with smoking. (Source:NIH).The most consistent finding, over decades of research, is the strong association between tobacco use and cancers of many sites. Hundreds of epidemiologic studies have confirmed this association.
Further support comes from the fact that lung cancer death rates in the United States have mirrored smoking patterns, with increases in smoking followed by dramatic increases in lung cancer death rates and, more recently, decreases in smoking followed by decreases in lung cancer death rates in men.