The heritability of mammographic breast density and circulating sex-hormone levels: two independent breast cancer risk factors.
BACKGROUND
Mammographic breast density and endogenous sex-hormone levels are both strong risk factors for breast cancer. This study investigated whether there is evidence for a shared genetic basis between these risk factors.


METHODS
Using data on 1,286 women from 617 families, we estimated the heritabilities of serum estradiol, testosterone, and sex-hormone binding globulin (SHBG) levels and of three measures of breast density (dense area, nondense area, and percentage density). We tested for associations between hormone levels and density measures and estimated the genetic and environmental correlations between pairs of traits using variance and covariance components models and pedigree-based maximum likelihood methods.


RESULTS
We found no significant associations between estradiol, testosterone, or SHBG levels and any of the three density measures, after adjusting for body mass index (BMI). The estimated heritabilities were 63%, 66%, and 65% for square root-transformed adjusted percentage density, dense area, and nondense area, respectively, and 40%, 25%, and 58% for log-transformed-adjusted estradiol, testosterone, and SHBG. We found no evidence of a shared genetic basis between any hormone levels and any measure of density, after adjusting for BMI. The negative genetic correlation between dense and nondense areas remained significant even after adjustment for BMI and other covariates (ρ = -0.34; SE = 0.08; P = 0.0005).


CONCLUSIONS
Breast density and sex hormones can be considered as independent sets of traits.


CONCLUSIONS
Breast density and sex hormones can be used as intermediate phenotypes in the search for breast cancer susceptibility loci.
Department of Public Heath and Primary Care, Centre for Cancer Genetic Epidemiology, University of Cambridge, Cambridge, UK.
Jajini S
JS
Varghese
Paula L
PL
Smith
Elizabeth
E
Folkerd
Judith
J
Brown
Jean
J
Leyland
Tina
T
Audley
Ruth M L
RM
Warren
Mitchell
M
Dowsett
Douglas F
DF
Easton
Deborah J
DJ
Thompson
D000368:Aged; D000071060:Breast Density; D001943:Breast Neoplasms / Q000097:blood* / Q000000981:diagnostic imaging / Q000235:genetics / Q000473:pathology*; D004958:Estradiol / Q000097:blood; D005260:Female; D012739:Gonadal Steroid Hormones / Q000097:blood*; D006801:Humans; D042361:Mammary Glands, Human / Q000002:abnormalities / Q000473:pathology; D008875:Middle Aged; D011859:Radiography; D012307:Risk Factors
D012739:Gonadal Steroid Hormones; D004958:Estradiol