A case of castration-refractory prostate cancer showing marked decrease of serum PSA level after zoledronic acid treatment with estramustine phosphate and prednisolone

A 66-year-old man was referred to our outpatient clinic for an elevated serum prostatic-specific antigen (PSA 4,319 ng/ mL). Magnetic resonance imaging (MRI) showed multiple metastatic lesions in the bones. The patient had received androgen deprivation therapy, but six months after treatment, he was diagnosed as having prostate cancer refractory to hormones. Combined treatment with docetaxel (DOC 30 mg/m2/week )and estramustine phosphate (EMP 560 mg/day) was initiated as first-line chemotherapy, but the treatment was discontinued because of side effects. Then, treatment with zoledronic acid was started(4 mg/4 weeks)and the PSA level decreased dramatically from 457.2 ng/mL to 5.5 ng/mL. Seven months after the diagnosis of CRPC, MRI showed a decrease ofbone metastases, and the PSA levels continued to decrease, eventually reaching 0.3 ng/mL. Zoledronic acid appears to not only show efficacy in preventing skeletal-related events, but has a potential antitumor effect in patients with metastatic CRPC.