RESUMEN
Tumor induced osteomalacia is uncommon and is characterized by an isolated and not PTH dependent reduction in tubular phosphate reabsorption. This alteration is produced by phosphaturic factors, such as fibroblast growth factor-23 (FGF-23) that are secreted by tumors. We report a 41 years old female presenting with joint pain and progressive loss of muscle strength in the lower limbs. Initial laboratory assessment showed hypophosphatemia, elevated alkaline phosphatases, normal intact parathormone levels, low levels of 25 hydroxy vitamin D and an elevated 24 h phosphaturia. Bone mineral density showed spine and femoral neck osteopenia. A positron emission tomography (PET) revealed a right thigh tumor with lung metastases. Its biopsy disclosed a fibrosarcoma. FGF-23 levels, measured by ELISA were markedly elevated. The patient was discharged with palliative measures.