Although estrogen replacement is routinely used to minimize fracture risks, side effects of estrogen include coronary heart disease, stroke, thromboembolic events, and breast cancer.27 Because FSH blocking antibodies prevent bone loss by inhibiting bone resorption and stimulating bone synthesis,28 our demonstration of bone FSH receptors in vivo provides the basis for designing FSH receptor antagonists to prevent bone loss in postmenopausal women contraindicated for the estrogen replacement therapy. This evidence concerns the gene FSHR and breast cancer.