Sex-hormone-binding globulin and breast cancer risk

We have measured serum concentrations of SHBG in 5000 women over the age of 35. In both premenopausal and postmenopausal women who were not suffering from cancer or other diseases or taking drugs likely to affect SHBG, the protein decreased with increasing weight and was lower in single nulliparous women than in married nulliparous women or parous women. In premenopausal women, SHBG was higher in women with late menarche. These findings suggest that diminished SHBG concentrations may be associated with the increased risk for breast cancer conferred by nulliparity and early menarche.