Tumor-induced osteomalacia: An overview.

Tumor-induced osteomalacia (TIO) is rare paraneoplastic syndrome of hypophosphatemic osteomalacia, caused by phosphaturic factors secreted by small mesenchymal origin tumors with distinct pathological features, called 'phosphaturic mesenchymal tumors'. FGF23 is the most well-characterized of the phosphaturic factors. Tumors are often small and located anywhere in the body from head to toe, which makes the localisation challenging. Functional imaging by somatostatin receptor-based PET imaging is the first line investigation, which should be followed with CT or MRI based anatomical imaging. Once localised, complete surgical excision is the treatment of choice, which brings dramatic resolution of symptoms. Medical management in the form of phosphate and active vitamin D supplements is given as a bridge to surgical management or in inoperable/non-localised patients. This review provides an overview of the epidemiology, pathophysiology, pathology, clinical features, diagnosis, and treatment of TIO, including the recent advances and directions for future research in this field.

[Clinical features, diagnostics and treatment of FGF23 secreting tumors: series of 40 clinical cases].

INTRODUCTION: Tumor-induced osteomalacia is an acquired rare disease manifested by hypophosphatemic osteomalacia due to excessive secretion of fibroblast growth factor 23 (FGF23). FGF 23 is a non-classical hormone secreted by bone tissue (osteocytes) and regulates phosphorus metabolism.The aim of this work is to present clinical experience in the diagnosis, treatment and rehabilitation of patients with tumor-induced osteomalacia. MATERIALS AND METHODS: 40 patients with clinically-confirmed tumor-induced osteomalacia were included in the study, 34 of whom had the tumor localized, 27 underwent surgical treatment and 21 achieved stable remission. RESULTS: The median age was 48 [41; 63] years, 43% were men, the time left from the the onset of the disease was 8 [4; 10] years. Biochemical findings were hypophosphatemia 0.47 [0.4; 0.53] mmol/l, a decrease in the tubular reabsorption phosphate 62 [52; 67]%, and an increase in alkaline phosphatase of 183 [112; 294] units/l. At the time of diagnosis, 100% had multiple pathological fractures, only 10% could move independently, and 77.5% classified the pain as unbearable (8-10 points according to the 10-point pain syndrome scale ). Among the methods used to detect tumors, the most sensitive were scintigraphy with tectrotide with SPECT/CT 71.4% (20/28) and MRI 90% (18/20). In 35% of cases, the tumor was localized in soft tissues and in 65% in bone tissue; The tumor was most often detected in the lower extremities, followed by the head in frequency of localization. 18 patients currently have no remission and they receive conservative treatment (phosphorus and alfacalcidol n=15 and burosumab n=3). In case of achieving remission (n=21), regression of clinical symptoms and restoration of bone and muscle mass was observed. Extensive excision of the tumor without prior biopsy resulted in the best percentage of remission - 87%. CONCLUSION: Tumor-induced osteomalacia is characterized by severe damage to bone and muscle tissue with the development of multiple fractures, muscle weakness and severe pain syndrome. In laboratory diagnostics, attention should be paid to hypophosphatemia, a decrease in the tubular reabsorption phosphate index and increased alkaline phosphatase. The use of functional diagnostic methods with a labeled somatostatin analogue to the subtype 2 receptor and MRI with contrast enhancement are the most accurate methods of topical diagnostics. In case of localization of the tumor, a wide excision without a preliminary biopsy is recommended.

Tumor-induced osteomalacia combined with increased bone resorption postoperatively: A case report.

RATIONALE: Rare tumor-induced osteomalacia (TIO) usually resulted in bone pain, fragility fractures and muscle weakness in clinical, which is caused by the reduced phosphate reabsorption, thus impaired mineralization of the bone matrix and free energy transfer. The specific problems in postsurgical patients are obscure although surgical removal of the tumor is the only definitive treatment. Here, we documented a female TIO patient who suffered more severe bone pain and muscle spasms post-operation. Further, we presented and discussed our explanation for the unexpected symptoms. PATIENT CONCERNS: The main symptoms were whole-body pain and muscle weakness. The patient also presented with osteoporosis and multiple fractures. DIAGNOSIS: Elevated serum fibroblast growth factor 23 (FGF23) level and hypophosphatemia indicated the diagnosis of TIO. Positron emission tomography (PET)/computed tomography (CT) with 68 Ga-DOTATATE located the tumor in the dorsolateral part of the left foot. Histopathological examinations confirmed the diagnosis. INTERVENTIONS: The tumor was surgically removed immediately after the diagnosis of TIO and localization of the tumor. Postoperatively, calcium carbonate supplement treatment was continued. OUTCOMES: Two days after surgery, the serum FGF23 level was decreased to the normal range. Five days after surgery, N-terminal propeptide of type I procollagen and ß-CrossLaps (ß-CTx) had a remarkable increase. A month after surgery, the patient N-terminal propeptide of type I procollagen and ß-CTx levels were decreased obviously, and serum FGF23, phosphate and 24h urinary phosphate were in the normal range. LESSONS: We report a female patient who presented with osteoporosis and fractures. She was found with an elevation of FGF23 and diagnosis with TIO after PET/CT scanning. After surgically removing the tumor, the patient experienced more severe bone pain and muscle spasms. Active bone remodeling might be the reason for the symptoms. Further study will reveal the specific mechanism for this abnormal bone metabolism.

[FGF23 tumor induced osteomalacia].

Tumor induced osteomalacia is a rare acquired disease. The cause is a mesenchymal tumor secreting fibroblast growth factor 23 (FGF23). An excessive amount of FGF 23 disrupts the metabolism of phosphorus and vitamin D, which leads to severe paraneoplastic syndrome, manifested in the form of multiple fractures, severe pain in the bones and generalized myopathy. With oncogenic osteomalacia, a complete cure is possible with radical resection of the tumor. Unfortunately, localization, small size of formations and rare frequency of occurrence lead to the fact that the disease remains unrecognized for a long time and leads to severe, disabling consequences. A step-by-step approach to diagnosis improves treatment outcomes. First, a thorough anamnesis is collected, then functional visualization is performed and the diagnosis is confirmed by anatomical visualization of the tumor. After that, the method of choice is a surgical treatment. If resection is not possible, then conservative therapy with active metabolites of vitamin D and phosphorus salts is indicated. New therapeutic approaches, such as the antibody to FGF23 or the pan-inhibitor of receptors to FGF, are actively developing. This article provides an overview of modern approaches to the diagnosis and treatment of this disease.

Intracranial phosphaturic mesenchymal tumors. A case report and review of literature.

Most osteomalacia-inducing tumors (OITs) are phosphaturic mesenchymal tumors (PMTs) that secrete fibroblast growth factor 23 (FGF23). These tumors usually occur in the bone and soft tissues, and intracranial OITs are rare. Therefore, intracranial OIT is difficult to diagnose and treat. This paper presents a case of intracranial OIT and shows a review of previous cases. A 45-year-old man underwent nasal cavity biopsy and treatment with active vitamin D3 and neutral phosphate for hypophosphatemia. Amplification of FGF23 mRNA level within the tumor was detected. Subsequently, the surgical specimen was diagnosed with a PMT and was considered the cause of the patient's osteomalacia. The patient was referred to a neurosurgery department for the excision of the intracranial tumor extending to the nasal cavity. After tumor removal, the serum levels of FGF23 and phosphorus were normalized as compared to preoperative those. The patient remains disease-free, without additional treatment, approximately 10 years after surgery, with no tumor recurrence. As per the literature, intracranial OITs usually occur in patients aged 8-69 years. Bone and muscle pain are major complaints. Approximately 60% of the patients reported previously had symptoms because of intracranial tumors. In some cases, it took several years to diagnose OIT after the onset of the osteomalacia symptoms. Laboratory data in such cases show hypophosphatemia and elevated FGF23 levels. Because FGF23 levels are associated with the severity of osteomalacia symptoms, total tumor resection is recommended. PMT and hemangiopericytoma (HPC) are histologically similar, but on immunochemistry, PMT is negative for signal transducer and activator of transcription 6 (STAT6), whereas HPC is positive. FGF23 amplification is seen in PMTs but not in HPCs. Therefore, the analysis of FGF23 and STAT6 was helpful in distinguishing PMTs from HPCs. In cases of hypophosphatemia and osteomalacia without a history of metabolic, renal, or malabsorptive diseases, the possibility of oncogenic osteomalacia should be considered.

Occult phosphaturic mesenchymal tumour of femur cortex causing oncogenic osteomalacia - diagnostic challenges and clinical outcomes.

BACKGROUND: Tumor induced osteomalacia (TIO) are extremely rare paraneoplastic syndrome with less than 300 reported cases. This report highlights the pitfalls and challenges in diagnosing and localizing TIO in patients with refractory and resistant osteomalacia. PATIENT AND METHODS: 41- year gentleman with 4-year history of musculoskeletal weakness and pathologic fractures presented in wheelchair bound incapacitated state of 1-year duration. Investigations were significant for severe hypophosphatemia, severe phosphaturia, normal serum calcium, reduced 1,25-dihydroxy vitamin-D, elevated ALP, elevated intact parathyroid hormone (iPTH), and pseudo-fractures involving pelvis and bilateral femur. Whole body MRI and 99mTc methylene diphosphonate bone-scan were also normal. Whole body FDG-PET scan involving all 4 limbs revealed a small FDG avid lesion at lateral border of lower end of left femur (SUV max 3.9), which was well characterized on 3-dimensional CT reconstruction. Plasma C-terminal fibroblast growth factor (FGF)-23 was 698 RU/ mL (normal < 150 RU/ml). Wide surgical excision of the tumor was done. Histopathology confirmed mesenchymal tumor of mixed connective tissue variant. Serum phosphorous normalized post-surgery day-1. High dose oral calcium and vitamin-D was continued. FGF-23 normalized post surgery (73RU/ml). Physical strength improved significantly and now he is able to walk independently. CONCLUSION: TIO is frequently confused with normocalcemic hyperparathyroidism and vitamin-D resistant rickets/osteomalacia, which increases patient morbidity. Imaging for tumor localization should involve whole body from head to tip of digits, cause these tumors are notoriously small and frequently involve digits of hands and legs. Complete surgical removal of the localized tumor is key to good clinical outcomes.

[Tumor-induced osteomalacia caused by a late-revealing phosphaturic mesenchymal tumor]. / Ostéomalacie secondaire à une tumeur mésenchymateuse phosphaturique de révélation tardive.

INTRODUCTION: Osteomalacia is associated with diffuse pain and multiple fractures and therefore, diagnosis and treatment of this condition are necessary. Clinicians should be aware of an uncommon mechanism of osteomalacia where hypophosphataemia is secondary to renal phosphaturia because of the production by a mesenchymal phosphaturic tumor of FGF-23. This tumor should be localized and removed to cure this tumor-induced osteomalacia. OBSERVATION: A 70-year-old female patient was admitted to explore diffuse pain caused by multiple fractures secondary to osteomalacia. Despite vitamin D supplementation, she remained profoundly hypophosphoremic with major renal phosphaturia. A tumor-induced mechanism was suspected because of high level of FGF-23. It took more than three years of investigation to spot the causal phosphaturic mesenchymal tumor despite annual repetition of indium-labelled scintigraphy and PET-scan. The resection of the tumor, located between two phalanges of the right foot, cured the patient with sustained normal rate of serum level of phosphorus after two years. CONCLUSION: Tumor-induced osteomalacia is a diagnostic challenge because the localization of the tumor may be a long process. Patients should be monitored clinically and imaging studies repeated until a diagnosis is made and the causal tumor removed.

Surgical Treatments of Tumor-Induced Osteomalacia Lesions in Long Bones: Seventeen Cases with More Than One Year of Follow-up.

BACKGROUND: Tumor-induced osteomalacia is a rare and fascinating paraneoplastic syndrome usually caused by a small, benign phosphaturic mesenchymal tumor. Most tumors are treated surgically, but we are unaware of any reports that compare the results of curettage and segmental resection for lesions in long bones. METHODS: Seventeen patients (ten male and seven female) with tumor-induced osteomalacia lesions in long bones, who underwent surgical treatment from December 2004 to August 2013 in our hospital, were included in this retrospective study. The mean follow-up (and standard deviation) was 35 ± 27 months (range, twelve to 116 months). The characteristics of the tumor and the effects of different surgical treatments (curettage compared with segmental resection) were evaluated. RESULTS: All patients showed typical clinical characteristics of tumor-induced osteomalacia, including elevated serum fibroblast growth factor-23 (FGF-23); 82% of tumors were in the epiphysis, and 82% grew eccentrically. The mean maximum diameter of the tumors was 2.4 ± 2.0 cm. The complete resection rates were similar for curettage (67%) and segmental resection (80%). However, the recurrence rate after curettage (50%) was higher than that after segmental resection (0%). The complete resection rate for secondary segmental resection (75%) was not different from that for primary segmental resection (83%). All of our cases of tumor-induced osteomalacia were caused by phosphaturic mesenchymal tumors. After successful removal of tumors, serum FGF-23 returned to normal within twenty-four hours and serum phosphorus levels returned to normal at a mean of 6.5 ± 3.5 days. CONCLUSIONS: Most lesions in long bones are located in the epiphysis, so curettage is first suggested to maintain joint function. If curettage is incomplete or there is a recurrence, secondary segmental resection should be considered curative. Changes of serum FGF-23 and phosphorus levels before and after the operation may be of prognostic help.

Tumor-Induced Osteomalacia: an Up-to-Date Review.

Tumor-induced osteomalacia (TIO) is a paraneoplastic syndrome resulting in renal phosphate wasting and decreased bone mineralization. TIO is usually induced by small, slowly growing tumors of mesenchymal origin (phosphaturic mesenchymal tumor mixed connective tissue variant [PMTMCT]). Nonspecific symptoms including fatigue, bone pain, and musculoskeletal weakness make the diagnosis elusive and often lead to a delay in treatment. The prognosis of TIO is excellent following complete resection of the neoplasm, which leads to the rapid and complete reversal of all symptoms. If the tumor cannot be detected, treatment relies on supplementation with phosphate and active vitamin D compounds. Subsequent radiotherapy in case of incompletely resected tumors or definitive radiotherapy in unresectable tumors is an important treatment option to avoid recurrence or metastasis even though this occurs rarely. Due to the risk of recurrence or late metastases, long-term monitoring is required even in TIO patients diagnosed with a benign tumor.

Phosphaturic mesenchymal tumors show positive staining for somatostatin receptor 2A (SSTR2A).

Tumor-induced osteomalacia (TIO) is a paraneoplastic syndrome associated with tumors that secrete phosphaturic hormones, most notably fibroblast growth factor 23 (FGF23). The majority of tumors associated with this syndrome show stereotypical histological features and are now known as phosphaturic mesenchymal tumors (PMTs). We postulated that immunohistochemistry for somatostatin receptor 2A (SSTR2A) could be used to definitively identify PMTs or other tumors that cause TIO. Immunohistochemistry for FGF23 and SSTR2A was performed on 15 tumors from 14 patients with a definite diagnosis of TIO. All showed positive staining for both markers. While FGF23 staining was quite focal in some tumors, SSTR2A showed diffuse strong expression. In 40 control tumors not known to be associated with the clinical or biochemical features of TIO, FGF23 expression was found in 2 cases (one aneurysmal bone cyst and one osteosarcoma). SSTR2A expression was found in 9 control tumors (4 synovial sarcomas, 2 hemangiomas, 2 aneurysmal bone cysts and one osteosarcoma). Only one tumor (an aneurysmal bone cyst) showed positive staining for both FGF23 and SSTR2A. SSTR2A also commonly stained neoplastic and non-neoplastic endothelial cells. We conclude that neither FGF23 nor SSTR2A expression are specific for the diagnosis of PMT. However both stains are highly sensitive. Because of its diffuse strong expression and widespread availability, immunohistochemistry for SSTR2A is useful to confirm the diagnosis of PMT in an appropriate setting particularly if material is limited. Negative staining can serve as an excellent rule out test for this diagnosis.

Incidental prostatic stromal tumor of uncertain malignant potential (STUMP): histopathological and immunohistochemical findings.

Stromal prostate tumors are rare neoplastic proliferative lesions that have been classified into prostatic stromal tumor of uncertain malignant potential (STUMP) and prostatic stromal sarcoma (SS) based on these criteria: stromal cellularity, presence of mitotic figures, necrosis, and stromal overgrowth. A prostatic stromal tumor of uncertain malignant potential (STUMP) is a non-epithelial, mesenchymal spindle-cell tumor that can be classified as a specialized stromal tumor of the prostate. STUMPs have the capability to diffusely infiltrate the prostate gland and extend into adjacent tissues. Furthermore, they often recur and this is why they are considered as neoplastic entities. STUMPs usually tend to be not aggressive, but occasional cases have been reported with an extension into adjacent tissues. A few cases develop a sarcomatous dedifferentiation. A 67-year-old male referred to the Department of Urology, Sapienza Rome University, with acute urinary retention (AUR) and bladder overdistention. Digital rectal examination (DRE) showed the presence of a severe prostatic hyperplasia and a transvesical prostatic adenomectomy (TVPA) was performed. The pathological evaluation performed at the Department of Pathology, Sapienza Rome University, revealed an incidental diagnosis of prostatic STUMP. The patient's follow-up is made every year with transrectal ultrasonography and nuclear magnetic resonance with spectroscopy, and every two years with a transperineal prostate biopsy to exclude a progression to a stromal sarcoma. After 5 years of follow-up the STUMP is still detectable but there is no sign of sarcoma. As a result of its relative rarity and lack of long-term follow-up, the prognosis of STUMP is unclear. Therapy varies from a wait-and-see approach to a radical retropubic prostatectomy.

Oncogenic osteomalacia from nasal cavity giant cell tumor.

BACKGROUND: Oncogenic osteomalacia is a rare paraneoplastic syndrome characterized by osteomalacia, which occurs as a result of excess renal phosphate excretion caused by fibroblast growth factor-23 secreted by mesenchymal tumors. This entity is rare in head and neck cancers. We report a rare case of oncogenic osteomalacia in a patient with an anterior skull base giant cell tumor. METHODS AND RESULTS: A 34-year-old woman presented with a 5-year history of progressive weakness in both lower limbs and the trunk. Hypophosphatemia and hypocalcemia had been noted by a local physician, but her symptoms persisted despite receiving calcium and vitamin D supplements. A recent onset of epistaxis and nasal blockage led to referral to the head and neck services. Nasal endoscopy revealed a left nasal cavity mass. Further evaluation with imaging studies revealed a mass in the nasal cavity with intracranial extension. Biopsy of the lesion suggested a neurogenic tumor. A putative diagnosis of anterior skull base neurogenic tumor with paraneoplastic hypophosphatemia was made. After the biochemical parameters were corrected, the patient underwent craniofacial resection. The final histopathologic study suggested the lesion as a "giant cell tumor." During the postoperative period the patient's biochemical and clinical symptoms improved dramatically, allowing her to regain normal mobility. CONCLUSIONS: Clinicians and pathologists must be aware of the clinical symptoms, laboratory abnormalities, and pathologic features of oncogenic osteomalacia, which may be caused by tumors in the head and neck and thus make an exhaustive effort to diagnose the same.

Tumor-induced osteomalacia.

Tumor-induced osteomalacia (TIO) is a rare and fascinating paraneoplastic syndrome in which patients present with bone pain, fractures, and muscle weakness. The cause is high blood levels of the recently identified phosphate and vitamin D-regulating hormone, fibroblast growth factor 23 (FGF23). In TIO, FGF23 is secreted by mesenchymal tumors that are usually benign, but are typically very small and difficult to locate. FGF23 acts primarily at the renal tubule and impairs phosphate reabsorption and 1α-hydroxylation of 25-hydroxyvitamin D, leading to hypophosphatemia and low levels of 1,25-dihydroxy vitamin D. A step-wise approach utilizing functional imaging (F-18 fluorodeoxyglucose positron emission tomography and octreotide scintigraphy) followed by anatomical imaging (computed tomography and/or magnetic resonance imaging), and, if needed, selective venous sampling with measurement of FGF23 is usually successful in locating the tumors. For tumors that cannot be located, medical treatment with phosphate supplements and active vitamin D (calcitriol or alphacalcidiol) is usually successful; however, the medical regimen can be cumbersome and associated with complications. This review summarizes the current understanding of the pathophysiology of the disease and provides guidance in evaluating and treating these patients. Novel imaging modalities and medical treatments, which hold promise for the future, are also reviewed.