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abstract
Background
It has been proposed that cancer is more common in some families than
in others, but the hypothesis lacks population level
support. We use a novel approach by
studying any cancers in large three-generation families and thus are
able to find risks
even though penetrance is low.
Methods
Individuals in the nation-wide Swedish Family-Cancer Database were
organised in three generations and the relative risk (RR)
of cancer was calculated to the
persons in the third generation by the numbers of patients with cancer
in generations 1, 2
and 3.
Results
The RRs for any cancer in generation 3 increased by the numbers of
affected relatives, reaching 1.61 when at least seven
relatives were diagnosed. The median
patient had two affected relatives, and 7.0% had five or more affected
relatives with
an RR of 1.46, which translated to
an absolute risk of 21.5% compared with 14.7% in population by age
65 years. For prostate
cancer, the RR was 2.85 with four or
more affected family members with any cancer, and it increased to 14.42
with four or
more concordant cancers in family
members. RRs for prostate cancer were approximately equal (2.70 vs 2.85)
if a man had one
relative with prostate cancer or
four or more relatives diagnosed with any cancer.
Conclusions
A strong family history of cancer, regardless of tumour type, increases
cancer risk of family members and calls for mechanistic
explanations. Our data provide tools
for counselling of patients with cancer with both low and high familiar
risks.
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