難治性低カルシウム･低リン血症をきっかけにFGF23高値を指摘された前立腺癌多発骨転移の1例

Abstract

A 53-year-old man was diagnosed with prostate cancer with multiple bone metastasis. Therefore androgen deprivation therapy was initiated. After treatment with denosumab injection for bone metastasis, hypocalcemia and hypophosphatemia occurred. Despite treatment for hypocalcemia with vitamin D and calcium lactate, his serum calcium and phosphate levels were refractory to treatment. The etiology of hypophosphatemia was investigated, and the level of serum fibroblast growth factor 23 (FGF23) was abnormally elevated. Three months after the first measurement of FGF23, the patient died of prostate cancer. Severe hypophosphatemia is a typical manifestation of tumor-induced hypophosphatemic osteomalacia (TIO), which is a paraneoplastic condition, mediated by FGF23 overexpression in most cases. His osteoblastic metastasis, however, did not meet the disease criteria of osteomalacia. Several reports have suggested that excessive FGF23 may mediate both severe hypophosphatemia and aggressive castrationresistant prostate cancer characteristics. Management of serum FGF23 may be a novel therapeutic strategy for castration-resistant prostate cancer with hypophosphatemia.