Causes of cancer--obesity

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Definition

Cancer is not just one disease, but a large group of almost one

hundred diseases. Its two main characteristics are uncontrolled

growth of the cells in the human body and the ability of these cells

to migrate from the original site and spread to distant sites. If

the spread is not controlled, cancer can result in death.

Description

One out of every four deaths in the United States is from cancer. It

is second only to heart disease as a cause of death in the states.

About 1.2 million Americans are expected to be diagnosed with cancer

in 1998, of which, more than 500,000 are expected to die.

Cancer can attack anyone. Since the occurrence of cancer increases

as individuals age, most of the cases are seen in adults, middle-

aged or older. The most common cancers are skin cancer, lung cancer,

colon cancer, breast cancer (in women), and prostate cancer (in

men). In addition, cancer of the kidneys, ovaries, uterus, pancreas,

bladder, rectum, and blood and lymph node cancer (leukemias and

lymphomas) are also included among the 12 major cancers that affect

most Americans.

Cancer, by definition, is a disease of the genes. A gene is a small

part of DNA, which is the master molecule of the cell. Genes

make " proteins, " which are the ultimate workhorses of the cells. It

is these proteins that allow our bodies to carry out all the many

processes that permit us to breathe, think, move, etc.

Throughout people's lives, the cells in their bodies are growing,

dividing, and replacing themselves. Many genes produce proteins that

are involved in controlling the processes of cell growth and

division. An alteration (mutation) to the DNA molecule can disrupt

the genes and produce faulty proteins. This causes the cell to

become abnormal and lose its restraints on growth. The abnormal cell

begins to divide uncontrollably and eventually forms a new growth

known as a " tumor " or neoplasm (medical term for cancer meaning " new

growth " ).

In a healthy individual, the immune system can recognize the

neoplastic cells and destroy them before they get a chance to

divide. However, some mutant cells may escape immune detection and

survive to become tumors or cancers.

Tumors are of two types, benign or malignant. A benign tumor is slow

growing, does not spread or invade surrounding tissue, and once it

is removed, it doesn't usually recur. A malignant tumor, on the

other hand, invades surrounding tissue and spreads to other parts of

the body. If the cancer cells have spread to the surrounding

tissues, then, even after the malignant tumor is removed, it

generally recurs.

A majority of cancers are caused by changes in the cell's DNA

because of damage due to the environment. Environmental factors that

are responsible for causing the initial mutation in the DNA are

called carcinogens, and there are many types.

There are some cancers that have a genetic basis. In other words, an

individual could inherit faulty DNA from his parents, which could

predispose him to getting cancer. While there is scientific evidence

that both factors (environmental and genetic) play a role, less than

10% of all cancers are purely hereditary. Cancers that are known to

have a hereditary link are breast cancer, colon cancer, ovarian

cancer, and uterine cancer. Besides genes, certain physiological

traits could be inherited and could contribute to cancers. For

example, inheriting fair skin makes a person more likely to develop

skin cancer, but only if they also have prolonged exposure to

intensive sunlight.

Causes & symptoms

The major risk factors for cancer are: tobacco, alcohol, diet,

sexual and reproductive behavior, infectious agents, family history,

occupation, environment and pollution.

According to the estimates of the American Cancer Society (ACS),

approximately 40% of the cancer deaths in 1998 will be due to

tobacco and excessive alcohol use. An additional one-third of the

deaths will be related to diet and nutrition. Many of the one

million skin cancers that are expected to be diagnosed in 1998, will

be due to over-exposure to ultraviolet light from the sun's rays.

Tobacco

Eighty to ninety percent of the lung cancer cases occur in smokers.

Smoking has also been shown to be a contributory factor in cancers

of upper respiratory tract, esophagus, larynx, bladder, pancreas,

and probably liver, stomach, and kidney as well. Recently,

scientists have also shown that second-hand smoke (or passive

smoking) can increase one's risk of developing cancer.

Alcohol

Excessive consumption of alcohol is a risk factor in certain

cancers, such as liver cancer. Alcohol, in combination with tobacco,

significantly increases the chances that an individual will develop

mouth, pharynx, larynx and esophageal cancers.

Diet

Thirty five percent of all cancers are due to dietary causes.

Excessive intake of fat leading to obesity has been associated with

cancers of the breast, colon, rectum, pancreas, prostate, gall

bladder, ovaries and uterus.

Sexual and reproductive behavior

The human papilloma virus, which is sexually transmitted has been

shown to cause cancer of the cervix. Having too many sex partners

and becoming sexually active early has been shown to increase one's

chances of contracting this disease. In addition, it has also been

shown that women who don't have children or have children late in

life, have an increased risk for both ovarian and breast cancer.

Infectious agents

In the last 20 years, scientists have obtained evidence to show that

approximately 15% of the world's cancer deaths can be traced to

viruses, bacteria, or parasites. The most common cancer-causing

pathogens and the cancers associated with them are shown in table

form.

Family history

Certain cancers like breast, colon, ovarian and uterine cancer,

recur generation after generation in some families. A few cancers,

such as the eye cancer " retinoblastoma, " a type of colon cancer, and

a type of breast cancer known as " early-onset breast cancer, " have

been shown to be linked to certain genes that can be tracked within

a family. It is therefore possible that inheriting particular genes

makes a person susceptible to certain cancers.

Occupational hazards

There is evidence to prove that certain occupational hazards account

for 4% of all cancer deaths. For example, asbestos workers have an

increased incidence of lung cancer. Similarly, a higher likelihood

of getting bladder cancer is associated with dye, rubber and gas

workers; skin and lung cancer with smelters, gold miners and arsenic

workers; leukemia with glue and varnish workers; liver cancer with

PVC manufacturers; and lung, bone and bone marrow cancer with

radiologists and uranium miners.

Environment

Radiation is believed to cause 1-2% of all cancer deaths. Ultra-

violet radiation from the sun accounts for a majority of melanoma

deaths. Other sources of radiation are x rays, radon gas, and

ionizing radiation from nuclear material.

Pollution

Several studies have shown that there is a well-established link

between asbestos and cancer. Chlorination of water may account for a

small rise in cancer risk. However, the main danger from pollution

occurs when dangerous chemicals from the industries escape into the

surrounding environment. It has been estimated that 1% of cancer

deaths are due to air, land and water pollution.

Cancer is a progressive disease, and goes through several stages.

Each stage may produce a number of symptoms. Some symptoms are

produced early and may occur due to a tumor that is growing within

an organ or a gland. As the tumor grows, it may press on the nearby

nerves, organs and blood vessels. This causes pain and some pressure

which may be the earliest warning signs of cancer.

Despite the fact that there are several hundred different types of

cancers, producing very different symptoms, the ACS has established

the following seven symptoms as possible warning signals of cancer:

Changes in the size, color, or shape of a wart or a mole

A sore that does not heal

Persistent cough, hoarseness, or sore throat

A lump or thickening in the breast or elsewhere

Unusual bleeding or discharge

Chronic indigestion or difficulty in swallowing

Any change in bowel or bladder habits.

Many other diseases, besides cancer, could produce the same

symptoms. However, it is important to have these symptoms checked,

as soon as possible, especially if they linger. The earlier a cancer

is diagnosed and treated, the better the chance of it being cured.

Many cancers such as breast cancer may not have any early symptoms.

Therefore, it is important to undergo routine screening tests such

as breast self-exams and mammograms.