Efficacy of YM-175, a new bisphosphonate, in the treatment of metastatic bone tumor from breast cancer and its effect on scintigraphy

Background: Bisphosphonates are powerful inhibitors of osteoclast-mediated bone resorption. They are effective in the treatment of Paget's disease of the bone, tumor-associated hypercalcemia, and osteoporosis. They are also used to treat metastatic bone disease. YM-175 is a new highly potent bisphosphonate. Bisphosphonates are also used as radiopharmaceuticals in bone scintigraphy. The data remain unclear as to whether or not the administration of large amounts of bisphosphonate interferes with the bone scintigraphy process. Methods: We have treated 8 patients with bone metastases from breast cancer with 10 mg IV, once a week for 5 weeks. The monitoring of bone pain, laboratory analysis with bone metabolic markers, and bone imaging including x-ray and bone scintigraphy, was performed for 8 weeks. A quantitative method was employed to evaluate serial bone scintigraphy. Results: Bone pain improved in 5 out of 8 cases at 2 and 4 weeks post-treatment without serious adverse effects, but the duration of pain relief was short. Markers of osteoclast activity were decreased significantly to a minimum at 2 weeks. No significant changes were shown in markers of osteoblast activity or in serum calcium levels. Intact parathyroid hormone (PTH) was elevated at 2 and 4 weeks. It appears that YM-175 suppressed osteoclast activity, however, its effect was negated by a PTH elevation response. No changes were detected in either x-ray findings or serial bone scintigraphy by use of visual images and quantitative methods. Conclusion: YM-175, a new bisphosphonate, was a safe and promising drug for the treatment of metastatic bone pain from breast cancer. Osteoclast activity was suppressed by bisphosphonate treatment, but, the PTH response negated the osteoclast suppression. Furthermore, YM-175 treatment did not alter bone scintigraphic images.