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In a recent editorial in the British Medical Journal, several experts
from the University of Bristol in England write about the substantial
and still growing body of evidence implicating insulin-like growth factor-I
(IGF-1) in cancer.
They note that the role of IGF-1 in promoting cancer has been investigated
for many years, but recently the quality and quantity of evidence has
increased
They note that several prospective studies have
used stored blood collected up to 14 years before the onset of cancer
have shown associations between IGF-1 and prostate cancer, premenopausal
breast cancer, and colon cancer.
According to the editorial, "The
risk of cancer is higher among people with raised concentrations of insulin-like
growth factor-I".
In addition, "it is lower among those with
high concentrations of insulin-like growth factor binding protein-3 (the
main binding protein)."
Research suggests that the observed relation between
cancer and IGF-1 is not due to the release of the growth factor by the
cancer itself.
"The effects are sizeable
and stronger than the effects seen in relation to most previously reported
risk factors" they state.
In addition to the increasing direct epidemiological
evidence, there is a significant amount of circumstantial evidence.
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Acromegaly, in which high concentrations
of growth hormone stimulate production of high concentrations of
IGF-1, has been associated with an increased risk of colorectal
cancer and breast cancer in some studies and less consistently with
prostate, thyroid, and hematological malignancies.
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In many studies anthropometric markers of
the activity of insulin-like growth factor-I, such as height and
leg length, are associated with cancer incidence, particularly with
the cancers for which risk increases with rising concentrations
of insulin-like growth factor-I.
- In animals, calorie restriction reduces the
risk of cancer primarily by reducing the circulating concentrations
of insulin-like growth factor-I" the editorial notes.
Some of the potential mechanisms of the way in
which IGF-1 increases cancer risk are as follows:
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IGF-1 could be a surrogate for the activity
of sex steroid hormones, which in turn influence the risk of cancer.
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IGF-1 may increase cell turnover and the
susceptibility of cells to malignant transformation both directly
and by modulating the effects of sex steroids.
- IGF-1 might increase the risk of cancer by
preventing the programmed death of cells that have been transformed,
thus interrupting an important process, which retards the development
of cancer.
"Given the increasing evidence
of the risk of cancer, caution should be exercised in the exogenous use
of either insulin-like growth factor-I or substances that increase concentrations
of it," they state.
British Medical
Journal October 7, 2000;321:847-848
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