Cancer Overview – Causes of Cancer
Every year, more than 560,000 people die of cancer in the United
States. It is only second to cardiovascular or heart disease as
the leading cause of death. Cancer is predominantly a disease
of older adults – about 70% of those who die of cancer are
65 years or older.
Carcinogenesis or Development of Cancer
Cancer results when normal cell transforms into a malignant growth
in a process called carcinogenesis. Cancer cells
proliferate or grow uncontrollably, and can spread to nearby tissue
and even to tissues far away from the original site through the
blood or lymphatic vessels in a process called metastatis.
It can also spread by unintentional transplantation during surgery.
Cancer develops because of mutations in the genes of the cells.
There are two types of genetic susceptibility to cancer:
- Oncogenes
These are genes that activate cell division and are involved
in embryo development.
- Tumor suppressor genes
Genes that stop cell division.
These genes are found in all normal cells. Mutations in these
cells, either inherited (or also called genetic mutation)
or caused by exposure to cancer-causing chemicals or carcinogens
(called acquired mutations) can cause normal cells to
become malignant, cancerous cells. The exact mechanism of cancer
development or carcinogenesis is complicated. Current medical
understanding is that interaction of carcinogens and accumulated
mutations in several genes are involved.
Carcinogens
Exposure of the following carcinogens can cause cancer:
- Tobacco
Smoking is the leading cause of preventable deaths in the Untied
States, and is responsible for about 85% of deaths due to lung
cancer. Tobacco is also linked to increased risk for cancers
of the mouth, larynx (respiratory tract), esophagus (food tract),
kidney, pancreas, bladder, and cervix.
A word on tobacco: there are many cancer-causing hazards that
we may not have control over, but smoking is not one of them.
Do not continue to jeopardize your health by smoking, and to
jeopardize the health of those around you (through second-hand
smoke). While quitting smoking is difficult, it is undoubtedly
the best health decision you can make.
- Radiation
High-energy or ionizing radiations can cause damage to the cell’s
DNA, leading to cancer-causing mutations.
Controlled radiation can actually be used to treat cancer –
by concentrating the dosage only to the cancer cells, radiation
can be used to selectively kill rapidly dividing, cancerous
cells.
X-rays, a valuable medical tool for diagnosing diseases, does
contain ionizing radiation. However, its does is about 1,000th
of that used in cancer treatment, and does not pose a significant
risk for cancer.
- Ultraviolet Radiation
Prolonged exposure to sunlight and ultraviolet radiation (through
tanning lamps) can cause damage to skin cells that lead to skin
cancers, such as basal cell and squamous cell carcinomas and
the deadly melanomas.
To minimize the risk of skin cancer, it is recommended that
you wear long sleeves and hats while outdoors in addition to
using sunscreens (with protective factor or SPF of 15 or higher).
- Chemicals
Various environmental pollutants and chemicals can pose risk
to workers who are regularly subjected to them. These chemicals
include asbestos, industrial dyes, heavy metals such as nickels,
acids such as chromic acid or chromate, vinyl chloride, a class
of organic compounds called benzene and benzopyrene.
- Viruses
Several viruses have been linked to increased risk of cancer.
| Virus |
Disease |
Cancer |
| Human Immunodeficiency Virus (HIV) |
Acquired Immunodeficiency Syndrome (AIDS) |
Hepatoma (Liver Cancer), Lymphoma
Sarcoma |
| Hepatitis B Virus (HBV) |
Hepatitis B |
Hepatoma |
| Epstein-Barr Virus (EBV) |
Mononucleosis |
Burkitt's Lymphoma,
Nasopharyngeal cancer |
| Human papilloma virus |
Genital wart |
Cervical cancer |
| Herpes Simplex Virus 2 (HSV-2) |
Genital herpes |
Cervical cancer |
Diet
In addition to the factors above, food and diet may also play
a big role in cancer. For example, high animal fat diet has been
linked to gastrointestinal cancer. Food additives containing nitrates
as well as charbroiling may also be a factor.
Hormones and Cancer
The role of hormones in carcinogenesis or the development of
cancer is still controversial. However, laboratory studies have
shown that excessive use of hormones, such as estrogen, in animals
can lead to cancer.
In rare cases, synthetic estrogen (diethylstilbestrol) has been
linked to vaginal cancer in daughters of women taking this hormone.
Hereditary Factors
Genetics play a significant role in many forms of cancer, such
as breast and ovarian cancers, retinoblastoma, hereditary nonpolyposis
colorectal cancer, and colon cancer. In these cases, common characteristics
of cancers caused by genetic factors include:
- Early onset of the disease
- Cancer occurring in both paired organs (for example, cancer
in both breasts, adrenal glands, and kidneys)
- Multiple growths
- Abnormal chromosomes sets or complement in tumor cells
