Clinical experience with the human monoclonal antibody anti-RANKL (denosumab), which is documented to be effective in non meta-static prostate and breast cancer as well as in postmenopausal osteoporosis, as well as with the parathyroid hormone derived peptides, with hormone analogues and selective estrogen receptor modulators, is still limited in HSCT recipients [30, 45, 46]. The gene discussed is ESR1; the disease is breast carcinoma.