Early phase endocrine-expansive breast and prostate cancers are treated with post-operative adjuvant hormonal therapies and chemotherapeutic drugs that have a negative impact on bone heath, blocking estrogen or androgen activity and increasing bone turnover leading to a progressively higher risk of fractures. At present, DXA monitoring of bone loss is widely recommended in prostate and breast cancer patients, but most fractures occur in patients whose DXA result falls outside the osteoporosis ranges, indicating that DXA might not be the elective exam for evaluating the degree of fracture risk in terms of microarchitecture alterations. The recently introduced Bone Structure Index (BSI) gives an indication of the quality of the bone structure. In this work, we discuss the preliminary results obtained in the evaluation of the BSI in female patients undergoing breast cancer treatment.