What Causes Cancer?
There is no one single cause for cancer. Scientists
believe that it is the interaction of many factors
together that produces cancer. The factors involved
may be genetic, environmental, or constitutional
characteristics of the individual.
Diagnosis, treatment, and prognosis for childhood
cancers are different than for adult cancers. The
main differences are the survival rate and the cause
of the cancer. The overall five-year survival rate
for childhood cancer is about 80%, while in adult
cancers the survival rate is 68%. This difference is
thought to be because childhood cancer is more
responsive to therapy and a child can tolerate more
Childhood cancers often occur or begin in the stem
cells, which are simple cells capable of producing
other types of specialized cells that the body
needs. A sporadic (occurs by chance) cell change or
mutation is usually what causes childhood cancer. In
adults, the type of cell that becomes cancerous is
usually an epithelial cell. Epithelial cells line
the body cavity and cover the body surface. Cancer
occurs from environmental exposures to these cells
over time. Adult cancers are sometimes referred to
as acquired for this reason.
Cancer Risk Factors
As mentioned, some cancers, particularly in adults,
have been associated with repetitive exposures or
risk factors. A risk factor is anything that may
increase a person's chance of developing a disease.
A risk factor does not necessarily cause the
disease, but it may make the body less resistant to
it. The following risk factors and mechanisms have
been proposed as contributing to cancer:
Lifestyle factors. Smoking, a high-fat
diet, and working with toxic chemicals are
examples of lifestyle choices that may be risk
factors for some adult cancers. Most children with
cancer, however, are too young to have been
exposed to these lifestyle factors for any
Family history, inheritance, and genetics may
play an important role in some childhood
It is possible for cancer of varying forms to be
present more than once in a family. It is unknown
in these circumstances if the disease is caused by
a genetic mutation, exposure to chemicals near a
family's residence, a combination of these
factors, or simply coincidence.
Some genetic disorders.
For example, Wiskott-Aldrich and
Beckwith-Wiedemann syndrome are known to alter the
immune system. The immune system is a complex
system that functions to protect our bodies from
infection and disease. The bone marrow produces
cells that later mature and function as part of
the immune system. One theory suggests that the
cells in the bone marrow, the stem cells, become
damaged or defective, so when they reproduce to
make more cells, they make abnormal cells or
cancer cells. The cause of the defect in the stem
cells could be related to an inherited genetic
defect or exposure to a virus or toxin.
Exposures to certain viruses.
Epstein-Barr virus and HIV, the virus that causes
AIDS, have been linked to an increased risk of
developing certain childhood cancers, such as
Hodgkin and non-Hodgkin lymphoma. Possibly, the
virus alters a cell in some way. That cell then
reproduces an altered cell and, eventually, these
alterations become a cancer cell that reproduces
more cancer cells.
Environmental exposures. Pesticides,
fertilizers, and power lines have been researched
for a direct link to childhood cancers. There has
been evidence of cancer occurring among nonrelated
children in certain neighborhoods and/or cities.
Whether prenatal or infant exposure to these
agents causes cancer, or whether it is a
coincidence, is unknown
Some forms of high-dose chemotherapy and
In some cases, children who have been exposed to
these agents may develop a second malignancy later
in life. These strong anticancer agents can alter
cells and/or the immune system. A second
malignancy is a cancer that appears as a result
from treatment of a different cancer.
How do genes affect cancer growth?
The discovery of certain types of genes that
contribute to cancer has been an extremely important
development for cancer research. Over 90% of cancers
are observed to have some type of genetic
alteration. Some of these alterations are inherited,
while others are sporadic, which means they occur by
chance or occur from environmental exposures
(usually over many years).
Types of cancer genes
There are three main types of genes that can affect
cell growth and are altered (mutated) in certain
types of cancers, including the following:
These genes regulate the normal growth of cells.
Scientists commonly describe oncogenes as similar
to a cancer "switch" that most people have in
their bodies. What "flips the switch" to make
these oncogenes suddenly become unable to control
the normal growth of cells and allowing abnormal
cancer cells to begin to grow, is unknown.
Tumor suppressor genes:
These genes are able to recognize abnormal growth
and reproduction of damaged cells, or cancer
cells, and can interrupt their reproduction until
the defect is corrected. If the tumor suppressor
genes are mutated, however, and they do not
function properly, tumor growth may occur.
These genes help recognize errors when DNA is
copied to make a new cell. If the DNA does not
"match" perfectly, these genes repair the mismatch
and correct the error. If these genes are not
working properly, however, errors in DNA can be
transmitted to new cells, causing them to be
Usually the number of cells in any of our body
tissues is tightly controlled so that new cells are
made for normal growth and development, as well as
to replace dying cells. Ultimately, cancer is a loss
of this balance due to genetic alterations that "tip
the balance" in favor of excessive cell growth.