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Case Report Tumour-induced Osteomalacia Tumour-induced Osteomalacia Secondary to a Sarcoma Karla Victoria Rodriguez-Velver, 1 María Azucena Zapata-Rivera, 1 Juan Montes-Villarreal, 1 Fernando Javier Lavalle-González, 1 José Gerardo González-González, 1 Jesús Zacarías Villarreal-Pérez 1 and Rene Rodríguez-Gutierrez 1,2,3 1. Endocrinology Division, University Hospital “Dr. Jose E. Gonzalez”, Medical School, Autonomous University of Nuevo Leon, Monterrey, Mexico; 2. Knowledge and Evaluation Research Unit in Endocrinology, Mayo Clinic, Rochester, Minnesota, US; 3.Division of Endocrinology, Diabetes, Metabolism and Nutrition, Mayo Clinic, Rochester, Minnesota, US T umour-induced osteomalacia (TIO), is a rare paraneoplasatic syndrome found in >95% of benign tumours that secrete fibroblast growth factor 23 - a phosphaturic circulating hormone. A rare case of a TIO secondary to a sarcoma, in a 21-year old man with history of bone fractures and distinctive physical and biochemical characteristics is presented and discussed. Keywords Tumour-induced osteomalacia, hypophosphatemia, fibroblast growth factor 23 Disclosure: Karla Victoria Rodriguez-Velver, María Azucena Zapata-Rivera, Juan Montes-Villarreal, Fernando Javier Lavalle-González, José Gerardo González-González, Jesús Zacarías Villarreal-Pérez, and Rene Rodríguez- Gutierrez have nothing to declare in relation to this article. No funding was received for the publication of this article. Compliance with Ethics: All procedures were followed in accordance with the responsible committee on human experimentation and with the Helsinki Declaration of 1975 and subsequent revisions, and informed consent was received from the patient involved in this case study. Open Access: This article is published under the Creative Commons Attribution Noncommercial License, which permits any non-commercial use, distribution, adaptation and reproduction provided the original author(s) and source are given appropriate credit. Received: 28 March 2016 Oncogenic osteomalcia, also known as tumour-induced osteomalacia (TIO), is a rare paraneoplasatic syndrome with around 350 reported cases. 1 TIO initial symptoms are nonspecific and include fatigue, bone pain, muscle weakness, weight, and height loss, and later bone deformity and fractures. It is characterised by hypophosphatemia, hyperphosphaturia, elevated alkaline phosphatase, and low serum 1-25(OH) vitamin D. Pathophysiologically, TIO is caused by tumours that secrete fibroblast growth factor 23 (FGF-23), a phosphaturic circulating hormone. TIO tumours are usually benign (in >95% of cases), however, they are a diagnostic challenge owing to their small size (usually less than 1 cm), which makes them difficult to localise. The differential diagnoses are genetic causes such as X-linked hypophosphatemic rickets, autosomal dominant and recessive hypophosphatemia, Dent’s disease, idiopathic hypercalciuria, and hereditary hypophosphatemic rickets with hypercaliuria. 2 Ten cases of TIO in the literature have been reported to be secondary to sarcomas, however, all of them were reported before it was known that the secreted molecule by these tumours was FGF-23, hence the diagnosis remained ‘uncertain’. Herein, we report the case of a 21-year-old male with a TIO associated with spindle cell sarcoma. Accepted: 3 May 2016 Citation: European Endocrinology, 2016;12(2):104–6 Corresponding Author: Rene Rodríguez-Gutiérrez, Servicio de Endocrinología. Hospital Universitario ‘Dr José E González’, Universidad Autónoma de Nuevo León, Madero y Gonzalitos S/N, Monterrey Nuevo León, 64460, México. E: Case report A 21-year-old man presented for evaluation of a pathological femur fracture. The patient had been otherwise healthy until age 18, when he noted onset of lower back pain after soccer practice, which was exacerbated by exercise and improved when being resting. This pain was progressive and he started noticing a loss of height. Over the next several months he experienced sudden, intense lower back pain and was diagnosed with a femur neck fracture. He had surgery with internal fixation, and stayed mainly in bed for the next 6 months. During this time, he recognised a growing tumour (around 2 cm) in the inner thigh of his right leg. This tumour progressively grew until it was around 4 x 10 cm. During this time he also lost height (going from 1.75 m to 1.65 m) and weight (losing 15–20 kg in total), and noticed kyphosis in the thoracic spine and sternum protrusion. While he was walking, he fell and suffered a pathologic right femoral fracture. On physical examination, his vital signs at presentation were normal and he was noted to have kyphosis, sternum protrusion, and no Harrison’s sulcus or pain at rib palpation (see Figure 1). Interestingly, a 4 x 10 cm tumour was noticed in the inner thigh of his right leg (rigid consistency, with rough edges, partially mobile and not painful). The neurologic evaluation and strength were unremarkable. A biochemical evaluation (Table 1) was noteworthy for severe hypophosphatemia associated with hyperphosphaturia and reduced tubular reabsorption of phosphorus (0.5 g in 24-hour collection), low serum 1, 25(OH) 2 D, increased serum alkaline phosphatase (ALP). The serum 25(OH) D levels were low and the FGF-23 was 389 RU/m. The remainder of the chemistry profile was within normal limits, including the serum calcium and intact parathyroid hormone (PTH). A diagnosis of hypophosphatemic osteomalacia due to a tumour was made. The magnetic resonance scanning demonstrated a 9 cm mass in the medial right femur, which involved bone and soft tissue (see Figure 2). 104 TOU C H ME D ICA L ME D IA