What is cancer?
Cancer is a group of many related diseases that begin in cells, the body's
basic building blocks. To understand cancer, it is helpful to know what happens
when normal cells become cancerous.
The body is made up of many types of cells. Normally, cells grow and divide to
produce more cells as they are needed to keep the body healthy. Sometimes, this
orderly process goes wrong. New cells form when the body does not need them,
and old cells do not die when they should. The extra cells form a mass of
tissue called a growth or tumor. Not all tumors are cancerous; tumors can be
benign or malignant.
Benign tumors are not cancer. They can often be removed and, in most cases,
they do not come back. Cells in benign tumors do not spread to other parts of
the body. Most important, benign tumors are rarely a threat to life.
Malignant tumors are cancer. Cells in malignant tumors are abnormal and divide
without control or order. Cancer cells invade and destroy the tissue around
them. Cancer cells can also break away from a malignant tumor and enter the
bloodstream or lymphatic system.
Blood vessels include a network of arteries, capillaries, and veins through
which the blood circulates in the body. The lymphatic system carries lymph and
white blood cells through lymphatic vessels (thin tubes) to all the tissues of
the body. By moving through the bloodstream or lymphatic system, cancer can
spread from the primary (original) cancer site to form new tumors in other
organs. The spread of cancer is called metastasis.
What causes cancer?
Scientists have learned that cancer is caused by changes in genes that normally
control the growth and death of cells. Certain lifestyle and environmental
factors can change some normal genes into genes that allow the growth of
cancer. Many gene changes that lead to cancer are the result of tobacco use,
diet, exposure to ultraviolet (UV) radiation from the sun, or exposure to
carcinogens (cancer-causing substances) in the workplace or in the environment.
Some gene alterations are inherited (from one or both parents). However, having
an inherited gene alteration does not always mean that the person will develop
cancer; it only means that the chance of getting cancer is increased.
Scientists continue to examine the factors that may increase or decrease a
person's chance of developing cancer.
Although being infected with certain viruses, such as the human papillomavirus
(HPV), hepatitis B and C (HepB and HepC), and human immunodeficiency virus
(HIV), increases the risk of some types of cancer, cancer itself is not
contagious. A person cannot catch cancer from someone who has this disease.
Scientists also know that an injury or bruise does not cause cancer.
Can cancer be prevented?
Although there is no guaranteed way to prevent cancer, people can reduce their
risk (chance) of developing cancer by:
· not using tobacco products
· choosing foods with less fat and eating more vegetables,
fruits, and whole grains
· exercising regularly and maintaining a lean weight
· avoiding the harmful rays of the sun, using sunscreen, and
wearing clothing that protects the skin
· talking with a doctor about the possible benefits of drugs
proven to reduce the risk of certain cancers
Although many risk factors can be avoided, some, such as inherited conditions,
are unavoidable. Still, it is helpful to be aware of them. It is also important
to keep in mind that not everyone with a particular risk factor for cancer
actually gets the disease; in fact, most do not. People who have an increased
likelihood of developing cancer can help protect themselves by avoiding risk
factors (see Question 2) whenever possible and by getting regular checkups so
that, if cancer develops, it is likely to be found and treated early. Treatment
is often more effective when cancer is detected early. Screening exams, such as
sigmoidoscopy or the fecal occult blood test, mammography, and the Pap test,
can detect precancerous conditions (which can be treated before they turn into
cancer) and early-stage cancer.
The NCI is conducting many cancer prevention studies to explore ways to reduce
the risk of developing cancer. These studies are evaluating dietary
supplements, chemopreventive agents, nutrition, personal behaviors, and other
factors that may prevent cancer.
What are some of the common signs and symptoms of cancer?
Cancer can cause a variety of symptoms. Possible signs of cancer include the
following:
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