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Alcohol and Cancer
Cancer kills an estimated 526,000 Americans yearly, second only to
heart disease (1). Cancers of the lung, large bowel, and breast are
the most common in the United States. Considerable evidence suggests
a connection between heavy alcohol consumption and increased risk
for cancer, with an
estimated 2 to 4 percent of all cancer cases thought to be caused
either directly or indirectly by alcohol (2).
A strong association exists between alcohol use and cancers of the
esophagus, pharynx, and mouth, whereas a more controversial
association links alcohol with liver, breast, and colorectal
cancers. Together, these cancers kill more than 125,000 people
annually in the United States (1). The following sections discuss
alcohol's role in these cancers.
What Is Cancer?
Cancer is a group of diseases characterized by cells that grow out
of control; in many cases, they form masses of cells, or tumors,
that infiltrate, crowd out, and destroy normal tissue. Although the
body strictly regulates normal cells to grow within the confines of
tissues, cancer cells reproduce independently, uninhibited by tissue
boundaries. Cancer develops
in three stages: initiation, promotion, and progression.
Cancercausing agents, known as carcinogens, can contribute to the
first two stages.
Cancer initiation occurs when a cell's DNA (the substance that genes
are made of) is irreversibly changed so that, once triggered to
divide, the cell will reproduce indefinitely. The "change" involves
mutations to the cell's genes that can occur spontaneously or can be
induced by a carcinogen. In some cancers, it has been shown that the
mutations occur in oncogenes, genes that normally promote cell
division, or in suppressor genes, genes that normally suppress cell
division. Thus, it is believed that cancer-causing mutations result
in overpromotion or undersuppression of cell reproduction.
During cancer promotion, the initiated cell is stimulated to divide.
The stimulus can be natural, as when tissue damage requires
proliferation of new cells, or it can be caused by a carcinogen.
During cancer progression, tumors produced by the replicating mass
of cells metastasize, or spread,
from the initial or primary tumor to other parts of the body,
forming secondarycancers.
Alcohol's Link to Cancer
Two types of research link
alcohol rehab and cancer.
Epidemiologic research has shown a dose-dependent
association between alcohol consumption and certain
types of cancer; as alcohol consumption increases, so
does risk of developing certain cancers. More tenuous
results have come from research into the mechanism by
which alcohol could contribute to cancer development.
Epidemiologic Research
The strongest link between alcohol and cancer involves
cancers of the upper digestive tract, including the
esophagus, the mouth, the pharynx, and the larynx (3).
Less consistent data link alcohol consumption and
cancers of the liver, breast, and colon (3).
Upper digestive tract. Chronic heavy drinkers have a
higher incidence of esophageal cancer than does the
general population. The risk appears to increase as
alcohol consumption increases (4-6). An estimated 75
percent of
esophageal cancers in the United States are attributable
to chronic, excessive alcohol consumption (7).
Nearly 50 percent of cancers of the mouth, pharynx, and
larynx are associated with heavy drinking (7). People
who drink large quantities of alcohol over time have an
increased risk of these cancers as compared with
abstainers (8,9). If they drink and smok e, the increase
in risk is even
more dramatic (5,6).
Liver. Prolonged, heavy drinking has been associated in
many cases with primary liver cancer. However, it is
liver cirrhosis, whether caused by alcohol or another
factor, that is thought to induce the cancer (10,11). In
areas of Africa and Asia, liver cancer afflicts 50 or
more people per 100,000 per year, usually associated
with cirrhosis caused by hepatitis
viruses. In the United States, liver cancer is
relatively uncommon, afflicting approximately 2 people
per 100,000, but excessive alcohol consumption is linked
to as many as 36 percent of these cases by some
investigators (2,12).
The association between alcohol use and liver cancer is
difficult to interpret, because liver cirrhosis and
hepatitis B and C virus infections often confound data
(13). Studies of the interactions between alcohol,
hepatitis viruses, and cirrhosis will help clarify these
associations with liver cancer (see below).
Breast. Chronic alcohol consumption has been associated
with a small (averaging 10 percent) increase in a
woman's risk of breast cancer (14-17). According to
these studies, the risk appears to increase as the
quantity and duration of alcohol consumption increases.
Other studies, however, have
found no evidence of such a link (18-20).
The inconsistency and weakness of epidemiologic findings
suggest that a third confounding factor, such as
nutrition, may be responsible for the link between
alcohol and breast
cancer (15). However, studies that adjusted for dietary
factors such as fat ntake found that the association
between alcohol and breast cancer remained (14,21,22).
Recent studies suggest that alcohol may play an indirect
role in the development of breast cancer. These studies
indicate that alcohol increases estrogen levels in
premenopausal women, which, in turn, may promote breast
cancer (23).
Colon. Epidemiologic studies have found a small but
consistent
dose-dependent association between alcohol consumption
and colorectal cancer (15,24), even when controlling for
fiber and other dietary factors (15,25,26). Despite the
large number of studies, however, causality cannot be
determined from the available data.
Other cancers. A few studies have linked chronic heavy
drinking with cancers of the stomach, pancreas, and
lungs (3). However, the association is consistently weak
and the majority of studies have found no association
(3).
Summary
Although epidemiologic studies have found a clear
association between alcohol consumption and development
of certain types of cancer, study findings are often
inconsistent and may vary by country and by type of
cancer. The key to understanding the association lies in
research designed
to decipher how alcohol may promote cancer. Such studies
examinealcohol's metabolic effects at the cellular and
genetic levels. Research examining the ways in which
alcohol may induce cancers has found some potential
mechanisms, the most promising of which implicates
oncogenes.
Alcohol and Cancer--A Commentary by
NIAAA Director Enoch Gordis, M.D.
As can be seen from this Alcohol Alert, the evidence for
alcohol's role in promoting some cancers (e.g., cancers
of the mouth and throat) is stronger than the evidence
linking alcohol use to other cancers, such as breast
cancer. Public health policy should reflect the str
ength of the evidence of
alcohol's role in promoting various cancers. Convincing
evidence of alcohol's effects on common cancers--even
when these effects are minor--has important public
health implications. However, it is equally important
that
the public not be subjected to undue alarm when evidence
for an increased risk for cancer due to alcohol use is
weak or inconclusive.
