A recent report from three Scandinavian clinical trials evaluating
tamoxifen therapy among breast cancer patients has raised concern
that tamoxifen therapy could increase the risk of a subsequent
colorectal malignancy. We propose to test the hypothesis that
tamoxifen use among breast cancer patients is associated with an
elevated risk of second primary colorectal cancer in a
The proposed study is a nested case-control investigation of new
primary colon and retal cancers among women with a prior
diagnosis of brest cancer. Women diagnosed with Stage I, II, or III
breast cancer between January 1, 1978 and December 31, 1992 will
be identified from the population-based Cancer Surveillance
System (CSS) of western Washington. All women in the study
cohort who are subsequently diagnosed with new primary colon or
retal cancer as their secondary primary cancer at least six months
following the unilateral diagnosis and before December 31, 1994
will be study cases (total, n=161). For each case, we will identify
at least two controls from the study cohort matched on the
following characteristics of the case at the time of unilateral
diagnosis: calendar year, age (in 5 year age groups), stage of
disease (I,II, or III) (n=361).
Tamoxifen therapy and other study information, will be obtained
by abstracting hospital medical records of cases and controls and
through a self-administered questionnaire sent to physicians who
were involved in each patients' care. Analyses will be conducted
to compare the relative risk of colorectal cancer in relation to the
duration and recency of tamoxifen use.
The success of tamoxifen as a breast cancer therapy, coupled with
the minimal short-term effects, has initiated interest in using
tamoxifen prophylactically in primary prevention of breast cancer.
It is reasonable to expect that long-term adverse effects will be
accepted and tolerated by most breast cancer patients, since
tamoxifen has demonstrated efficacy for this potentially
life-threatening disease. Such effects may not be acceptable to
healthy women, including those at higher than average risk for
breast cancer. It is important to document all beneficial and
adverse health effects associated with tamoxifen treatment so that
an informed decision can be made with respect to the prophylactic
use of the drug.
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