- Author: Colditz GA
- Title: Relationship between
estrogen levels, use of hormone replacement
therapy, and breast cancer.
- Source: J Natl Cancer Inst;
90(11):814-23 1998 UI: 98286833
Abstract
 "We sought to determine
the strength of the evidence suggesting
that estrogen and postmenopausal
replacement hormones play a role in the
development of breast cancer.
- We reviewed the existing
English language literature in MEDLINE on
hormones and breast cancer, including
reports on cell proliferation and
endogenous hormone levels, as well as
epidemiologic studies of the relationship
between the use of postmenopausal
hormones and the risk of breast cancer in
women.
- A factor that increases
the probability that cancer will develop
in an individual has been defined as a
cancer cause.
- The Hill criteria
for demonstrating a link between
environmental factors and disease
were used to review the evidence
for a causal relationship between
female hormones and breast
cancer.
 We found evidence
of a causal relationship between these
hormones and breast cancer, based on the
following criteria: consistency,
dose-response pattern, biologic
plausibility, temporality, strength of
association, and coherence.
 The magnitude of
the increase in breast cancer risk per
year of hormone use is comparable to that
associated with delaying menopause by a
year.
- The positive relationship
between endogenous hormone levels in
postmenopausal women and risk of breast
cancer supports a biologic mechanism for
the relationship between use of hormones
and increased risk of this disease.
 The finding that the increase in
risk of breast cancer associated with
increasing duration of hormone use does
not vary substantially across studies
offers further evidence for a causal
relationship.
 We conclude that
existing evidence supports a causal
relationship between use of estrogens and
progestins, levels of endogenous
estrogens, and breast cancer incidence in
postmenopausal women.
- Hormones may act to
promote the late stages of carcinogenesis
among postmenopausal women and to
facilitate the proliferation of malignant
cells.
- Strategies that do not
cause breast cancer are urgently needed
for the relief of menopausal symptoms and
the long-term prevention of osteoporosis
and heart disease. (99
Refs)"
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