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Dr. Greenwald Says Cancer Prevention Trials ‘Here to Stay’

Dr. Greenwald Says Cancer Prevention Trials ‘Here to Stay’

SEATTLE--Trials in the past decade offer the first evidence that some of
the most prevalent cancers in the population
are preventable, and a host of ongoing
trials are testing new prevention
strategies, Peter Greenwald, MD, DrPH, director of the National Cancer Institute's
Division of Cancer Prevention, said at
the 50th Annual Meeting of the Southwest
Oncology Group (SWOG). However,
he noted, critical challenges in the
future will include putting the knowledge
gained into practice and ensuring
an adequate supply of health care professionals
to implement prevention efforts.

Dr. Greenwald noted that this year
marks the 23rd anniversary of the Community
Clinical Oncology Program
(CCOP), the main mechanism by which
NCI provides funding for clinical cancer
prevention trials. The program currently
has 3,325 participating physicians, 390
participating hospitals, and 56 ongoing
cancer prevention and control trials.

Prostate Cancer Prevention
The Prostate Cancer Prevention Trial,
conducted among men who had a PSA
level of 3 ng/mL or lower, found that relative to placebo, finasteride was associated
with a roughly 25% reduction in
the incidence of prostate cancer of any
grade, but also with a higher incidence of
cancers of Gleason grades 7-10, Dr.
Greenwald said. Subsequent investigation
suggested that the latter finding was likely
due to a detection bias related to finasteride-
induced shrinkage of the prostate
and, therefore, a greater likelihood of hitting
a high-grade area of a cancer during
a biopsy. Furthermore, he noted, analyses
restricted to men with tumors of
Gleason grades 8-10 showed that among
those treated with finasteride, the tumors
were smaller and less often had aggressive

"Based on this SWOG-led study, we
have the first definitive evidence that
prostate cancer, at least in part, is preventable,"
Dr. Greenwald commented. "We also have a unique tissue bank with
controls that is helping in a major reevaluation
of the PSA test, and providing
a lead toward understanding, at a biological
level, what makes these tumors

He noted that further data on prostate
cancer prevention are awaited from
the Selenium and Vitamin E Cancer Prevention
Trial (SELECT), in which men
are receiving one or both supplements,
or placebos, for 7 years. "It is a wonderful
trial. It is in progress. It is tremendously
well run and managed," he said.

Breast Cancer Prevention
The Breast Cancer Prevention Trial
found that relative to placebo, tamoxifen
was associated with a nearly 50% reduction
in the incidence of breast cancer
among women at high risk, Dr. Greenwald
said. Further, the Multiple Outcomes
of Raloxifene Evaluation (MORE)
trial found a 76% reduction in the risk of
invasive breast cancers with raloxifene
(Evista), compared with placebo among postmenopausal women with osteoporosis.
"These two trials were the main driving
factor for the decision to initiate the
STAR [Study of Tamoxifen and Raloxifene]
trial, the head-to-head comparison
of tamoxifen and raloxifene," he said.

In the recently reported STAR trial,
among postmenopausal women, the two
drugs were equally effective in preventing
primary invasive breast cancer,
achieving reductions of 40% to 50%,
while raloxifene was less effective in preventing
noninvasive breast cancers.


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