NcXHF

HARVIE, HOWELL, AND EVANS
TABLE 2. Breast Cancer Prevention across the Life Course 66,67
Timing of Exposure
Before Menarche
After Menarche and
before First Birth
Premenopausal
Years
Postmenopausal Years
Links to pre- or postmenopausal breast cancer Pre Post Pre Post Pre Post Post
Greater adiposity or 2 or 2 or 2 or 2 1 1
Height growth velocity 1 1 NA NA NA NA NA
Sedentary lifestyle ? ? 1 1 1 1 1
High alcohol intake NA NA 1 1 1 1 1
Smoking ? ? 1 1
High soy intake 2 2 2 2
Abbreviations: NA, not applicable; Pre, premenopausal breast cancer; Post, postmenopausal breast cancer.
No effect.
2Decreased risk.
1Increased risk.
ers in positive cohort studies are between 1.1 and 1.4. The
effect of smoking appears to be mainly linked to ER-positive
cancers and among individuals with polymorphisms in genes
involved in the metabolism of tobacco products, such as
NAT2, although the current evidence is equivocal. 52
LIFESTYLE MODIFICATION OF RISK AMONG BRCA1
AND BRCA2 CARRIERS
Rates of breast cancer have increased among high-risk populations
with mutations in the BRCA1 and BRCA2 breast
cancer susceptibility genes, mirroring the increase in rates
among the general population over the last century. A published
data set from Iceland reported a fourfold increase in
the cumulative incidence of breast cancer (before age 70
years) between 1920 and 2000 among BRCA2 carriers (18.6%
to 71.9%) and women in the general population (1.8% to
7.5%). 54
A marked increased penetrance of BRCA mutations over
the years has been shown in a number of cohorts and is
thought to reflect increased reproductive and lifestyle risk
factors, although the exact causes remain unknown. Highquality
large-scale genome-wide association studies have
identifıed genetic variation in loci that affect BRCA penetrance.
In contradistinction, modifıable risk factors have
mainly been studied in small case-control studies with retrospective
collection of lifestyle risk information, which are often
confounded by ascertainment bias in clinic-based
settings and survival bias, and the fındings have not been validated
in independent replication sets. These studies have
produced equivocal evidence that risk among BRCA1 and
BRCA2 carriers is increased with weight and smoking and
TABLE 3. What Causes Breast Cancer? The Mismatch between Expert Opinion and Lay Perception
Expert Opinion (Estimated Attributable Risk [U.K]) 63 Common Beliefs among Healthy Women (1,297 patients) 68
Non-modifiable % of cases Non-modifiable * % citing this reason
Genetic factors** 47 Genetic factors 77.6
Reproductive factors: nulliparity, late parity, lack of breastfeeding 69 11 Environmental pollutants 31.7
Occupational–shift work 4.6 Stress 27.9
Potentially modifiable factors % of cases Food additives 18.4
Obesity 9.0 Pesticides 10.0
Alcohol consumption 6.4 Food additives 18.4
Physical activity 3.4 Reproductive 7.2
Use of HRT 3.2 Breast injury 6.6
Chance, fate/God’s will 6.5
Potentially modifiable factors % citing this reason
Diet 23.2
Alcohol 12.6
Physical activity 11.6
Smoking 11.6
Use of HRT 7.2
Abbreviations: HRT, hormone replacement therapy.
*Totals could exceed 100% as respondents could identify agents from multiple categories.
**DG Evans, personal communication, 2014.
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