A number of established prescription drugs
are being tested to see if they have useful anti-cancer
effects. Some groups of people might consider taking such
"chemopreventive" drugs for prophylactic purposes,
even if they are not ill. Some drugs have produced promising
results; but they do all have side-effects. The concept
of "chemoprevention" is best known in the case
of preventing heart disease, for example drugs used to lower
blood-cholesterol levels or to lower hypertension.
Up to now, the emphasis in cancer research
has been on curing the condition. While these efforts continue,
an increasing number of researchers are searching for drugs
or other supplements that will prevent or delay the onset
of cancer in the first place. Because of the side-effects,
this is not recommended for everybody; but two developments
now make the preventive approach using drugs more attractive.
It is now recognised that many cancers start out years earlier
as pre-malignant lesions, which in principle may be diagnosed.
Second, there is growing evidence of a genetic link to many
types of cancer, and this again enables at-risk groups of
people to be identified.
More than 50 clinical trials are underway,
testing various compounds and drugs for anti-cancer action.
A study published early in 2003 demonstrated that low doses
of aspirin can prevent development of pre-cancerous polyps
in persons with a family history of colon cancer. A large
study is currently underway which is testing whether selenium
and vitamin E supplementation can prevent prostate cancer.
Another investigation is testing the anti-inflammatory
drug Celebrex, used originally to treat arthritis. This
has already been shown to reduce pre-cancerous polyps in
patients with a rare genetic syndrome that causes colon
cancer. Now studies are evaluating whether it will also
help protect against the formation of such polyps in average
But the use of chemopreventive drugs is
controversial. This is partly because it is harder to pinpoint
who would most benefit from the treatment -- and thus weigh
against the potential risks. In the case of treating known
disease, this decision is much clearer. Thus cancer prevention
has usually focused on diet and lifestyle changes, rather
than using drugs. But for some people, particularly those
with an unfavorable genetic predisposition, such changes
may not be enough.
However, it should be pointed out that
some previous chemoprevention trials have produced unexpected
negative or confusing results. Some years ago the vitamin-A
precursor Beta-carotene seemed promising as a treatment
to reduce the risk of lung cancer. But trials on heavy smokers
showed that those taking this supplement actually got cancer
at a higher rate than the control group. Another not totally
encouraging example is the use of Finsteride to prevent
prostate cancer. In the trial, this drug clearly did reduce
the risk of getting prostate cancer. But the reported side-effects
included decreases in libido and potency, and, more worryingly,
those who did get cancer appeared to have a higher risk
of getting it in more severe form. More research is needed
to understand this effect.
A landmark study by the American
Association for Cancer Research, published in 2002, concludes
that many cancers start as pre-malignant lesions, that over
time develop into cancer. Many specialists argue that by
treating these lesions with drugs, the process by which
they become cancerous can be halted or at least delayed.
Finding these lesions is not so simple as measuring high
blood-cholesterol or hypertension; but screening techniques
are constantly advancing, and an aging population is becoming
more accustomed to regular health-screening tests. Treating
"pre-cancer" will probably be an increasing focus
of cancer-prevention efforts.