Oncogenic osteomalacia due to FGF23-expressing colon adenocarcinoma

A Rare Association Between Osteomalacia, Phosphaturic Mesenchymal Tumor, and Ovarian Cancer: A Case Report and Literature Review

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by hypophosphatemia, bone mineralization disorders with increased risk of fragility fractures, muscle pain, and progressive weakness. TIO has been associated with increased production of the phosphaturic hormone Fibroblast Growth Factor 23 (FGF23) usually by mesenchymal tumors of soft tissue or bone (Phosphaturic Mesenchymal Tumors-PMTs). In rare cases TIO may be observed in association with other malignancies. We report the case of a 66-year-old woman with an occasional diagnosis of both a PMT and an ovarian cancer during the evaluation of TIO. We also systematically review the literature to discover possible correlations between osteomalacia, FGF23 production, and ovarian cancer. Four studies were eligible for the analysis. Two case reports described an association between TIO development and ovarian cancer, whereas the two case-control studies hypothesized a possible correlation between FGF/FGF receptor axis and cancer development. Although it does not provide conclusive evidence regarding the association between TIO and ovarian cancer, this case report highlights the possibility that in the diagnostic workup of suspected TIO, both FGF23-secreting tumors distinct from PMT and tumors unrelated to the clinical presentation of TIO could be identified. This information is important for guiding successful tumor staging and determining the necessity for surgical intervention and/or eventual adjuvant therapy.

Acquired Forms of Fibroblast Growth Factor 23-Related Hypophosphatemic Osteomalacia

Fibroblast growth factor 23 (FGF23) is a pivotal humoral factor for the regulation of serum phosphate levels and was first identified in patients with autosomal dominant hypophosphatemic rickets and tumor-induced osteomalacia (TIO), the most common form of acquired FGF23-related hypophosphatemic rickets/osteomalacia (FGF23rHR). After the identification of FGF23, many other inherited and acquired forms of FGF23rHR were reported. In this review article, the detailed features of each acquired FGF23rHR are discussed, including TIO, ectopic FGF23 syndrome with malignancy, fibrous dysplasia/McCune-Albright syndrome, Schimmelpenning-Feuerstein-Mims syndrome/cutaneous skeletal hypophosphatemia syndrome, intravenous iron preparation-induced FGF23rHR, alcohol consumption-induced FGF23rHR, and post-kidney transplantation hypophosphatemia. Then, an approach for the differential diagnosis and therapeutic options for each disorder are concisely introduced. Currently, the majority of endocrinologists might only consider TIO when encountering patients with acquired FGF23rHR; an adequate differential diagnosis can reduce medical costs and invasive procedures such as positron emission tomography/computed tomography and venous sampling to identify FGF23-producing tumors. Furthermore, some acquired FGF23rHRs, such as intravenous iron preparation/alcohol consumption-induced FGF23rHR, require only cessation of drugs or alcohol to achieve full recovery from osteomalacia.

Tumor-induced Osteomalacia: A Case Report and Etiological Analysis with Literature Review

BACKGROUND

Tumor-induced osteomalacia (TIO) belongs to a rare disease of the paraneoplastic syndrome. Phosphate uric mesenchymal tumor (PMT) is the most common cause of TIO, while the possibility of other tumors cannot be excluded.

CASE PRESENTATION

We present a case of a 36-year-old female patient with systemic skeletal abnormalities. The woman complained of low back pain with mild motor dysfunction for 2 years. Laboratory examination showed abnormalities in markers of bone metabolism, parathyroid hormone (PTH), vitamin D and serum phosphorus. Pooled imaging examination indicated extension abnormalities in the skeletal system and a single lesion in the right femoral head. The lesion of the right femoral was imaging with somatostatin receptor-positive, which was highly suggestive of a single neuroendocrine tumor. CT guided right femoral tumorectomy and bone grafting were performed when medical treatment failed. Postoperative pathological diagnosis was phosphate urinary mesenchymal tumor secreting fibroblast growth factor 23 (FGF23), which accorded with pre-operative expectations. The postoperative symptoms were effectively relieved, and indicators returned to normal.

CONCLUSION

The tumors causing TIO exhibited significant heterogeneity in terms of tissue origin, pathological characteristics and biological behavior, but the unique common characteristic is the secretion of FGF23. With significant progress in diagnosis and treatment, the clinical follow-up of most TIO patients shows a good prognosis, but the prognosis of those with malignant tumors is relatively poor.

[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 in Patients With Malignancy: A Meta-analysis and Systematic Review of Case Reports

CONTEXT

Tumor-induced osteomalacia (TIO) due to fibroblast growth factor 23 (FGF23) overexpression is becoming recognized in patients with malignancy. The condition may be underdiagnosed, with a scarce medical literature.

OBJECTIVE

To perform a meta-analysis of case reports to allow a better understanding of malignant TIO and its clinical implications.

METHODS

Full texts were selected according to strict inclusion criteria. All case reports were included where patients had hypophosphatemia, malignant TIO, and FGF23 blood levels. Thirty-two of 275 eligible studies (n = 34 patients) met inclusion criteria. A list of desired data was extracted and graded for methodological quality.

RESULTS

Prostate adenocarcinoma (n = 9) were the most tumors reported. Twenty-five of 34 patients had a metastatic disease and a poor clinical outcome was reported for 15 of 28 patients. The median levels of blood phosphate and C-terminal FGF23 (cFGF23) were 0.40 mmol/L and 788.5 RU/mL, respectively. For most of patients, blood PTH was elevated or within range, and calcitriol levels were inappropriately low or normal. Alkaline phosphatase concentrations were increased for 20 of 22 patients. The cFGF23 values were significantly higher for patients with a poor clinical outcome when compared to other patients (1685 vs 357.5 RU/mL). In case of prostate cancer, cFGF23 levels were significantly lower (429.4 RU/mL) than for other malignancies (1007.5 RU/mL).

CONCLUSION

We report for the first time a detailed description of the clinical and biological characteristics of malignant TIO. In this context, FGF23 blood measurement would be of value for the diagnostic workup, prognostication, and follow-up of patients.

Evaluation of the trabecular bone score in 35 children and adults with X-linked hypophosphatemic rickets

INTRODUCTION

 The aim of this study is to evaluate and compare the trabecular bone scores (TBSs) of 11 children and 24 adults with X-linked hypophosphatemic rickets (XLH) and non-XLH subjects from a tertiary center.

MATERIALS AND METHODS

 The areal bone mineral density at the lumbar spine (LS-aBMD) and LS-aBMD Z score were analyzed by dual-energy X-ray absorptiometry. The bone mineral apparent density (BMAD) and LS-aBMD Z score adjusted for height Z score (LS-aBMD-HAZ) were calculated. The TBS was determined using TBS iNsight software based on DXA images from the Hologic QDR 4500 device.

RESULTS

The XLH patients exhibited a higher mean LS-aBMD Z score, BMAD, and TBS than the non-XLH subjects (p < 0.01). LS-aBMD-HAZ and BMAD were greater in the XLH children than those in their corresponding non-XLH subjects (p < 0.01 and p = 0.02), and the XLH children trended toward a greater TBS (p = 0.06). The XLH adults had a higher LS-aBMD Z score, BMAD, and TBS than the non-XLH subjects (p < 0.01). When stratified by metabolic status according to the serum values of bone formation markers, compensated adult patients had a higher LS-aBMD Z score, BMAD, and TBS than non-XLH subjects (p < 0.01). Noncompensated patients had higher LS-aBMD Z scores and BMAD results than non-XLH subjects. However, TBS values did not differ statistically significantly between those groups (p = 0.45).

CONCLUSION

The higher LS-aBMD Z score, BMAD, and TBS result in the XLH patients compared to non-XLH subjects indicates an increased amount of trabecular bone within the lumbar spine, regardless of extraskeletal calcifications.

Unusual phosphaturic mesenchymal tumor mimicking osteoid osteoma

Phosphaturic mesenchymal tumor is a rare tumor characterized by paraneoplastic osteomalacia. The diagnosis is often delayed because of nonspecific symptoms and difficulty to localize the tumor. In this study we report a case of PMT of the left femur detected by Ga-68-DOTATATE PET-CT with radiological features mimicking osteoid osteoma. We report a 31-year-old female patient who presented to our hospital for evaluation due to progressive bone pain and muscle weakness. Her laboratory data showed hypophosphatemia and increased fibroblast growth factor 23 (FGF-23) together with reduced bone mineral density on bone densitometry. The diagnosis of PMT was suspected and the tumor was identified on Ga-68-DOTATATE PET-CT as a focal uptake in a lucent lesion of the left femoral head with a central sclerotic dot mimicking a nidus as seen in osteoid osteoma. The lesion was treated with percutaneous radiofrequency ablation. Laboratory tests and bone densitometry rapidly improved post-treatment. The present case emphasizes the difficulty to diagnose PMT due to its nonspecific biochemical and clinical presentation and the relevance of functional imaging for locating these tumors despite different radiological presentation.

Refractory hypercalcemia of malignancy: a problem with many potential roots

Hypercalcemia of malignancy (HCM) is a common clinical problem that is associated with considerable morbidity and negative effects on quality of life. Despite the availability of effective medical treatments for HCM, options are needed for cases that are refractory to conventional therapies. In this context, "refractory" refers to reasonable control of calcium in the setting of inpatient hospitalization (after receipt of standard of care therapies, such as continuous intravenous fluids, calcitonin, and intravenous bisphosphonates) with relapse into severe hypercalcemia within days or weeks of discharge from the hospital. Here we discuss drivers of hypercalcemia of malignancy and the physiologic mechanisms whereby they operate to increase serum calcium. Additionally, we discuss multiple available treatments targeted to a given contributory mechanism and also briefly discuss potential future treatments in need of further study.

FGF23 promotes proliferation, migration and invasion by regulating miR-340-5p in osteosarcoma

BACKGROUND

Increasing evidences have been indicated that FGF23 is associated with the biological behavior of malignant tumors, but its role in osteosarcoma and the specific mechanism need to be elucidated. The purpose of this study is to investigate the effects of FGF23 on the proliferation, migration and invasion of osteosarcoma cells, and the possible molecular mechanisms.

METHODS

Western blot was used to detect differences in FGF23 expression in osteosarcoma cells MG-63 and U2-OS and osteoblasts hFOB1.19. FGF23-overexpressing adenoviruses and FGF-silencing plasmids were transfected into osteosarcoma cells, and transfection efficiency was verified using Western blot. MTT and colony formation assays were performed to detect osteosarcoma cell proliferation. Cell cycle was measured by flow cytometry. Scratch assay, holographic imaging cell analyzer Holomonitor ® M4 and transwell were applied to detect cell migration and invasion. Dual-luciferase reporter assay was performed to validate the interaction between FGF23 and miR-340-5p. Changes in miR-340-5p mRNA levels were measured by QRT-PCR.

RESULTS

FGF23 is highly expressed in osteosarcoma cells compared to hFOB1.19. Overexpression of FGF23 significantly promoted the proliferation, migration and invasion of MG-63 and U2-OS cells. MiR-340-5p is a target of FGF23. Transfection of miR-340-5p mimics reversed the promoting effects of FGF23 on proliferation, migration and invasion of MG-63 and U2-OS cells.

CONCLUSION

FGF23 promotes osteosarcoma cell proliferation, migration and invasion by targeting miR-340-5p gene expression.

Tumor-Induced Osteomalacia: A Systematic Clinical Review of 895 Cases

Tumor-induced osteomalacia (TIO) is a rare and largely underdiagnosed paraneoplastic condition. Previous reviews often reported incomplete data on clinical aspects, diagnosis or prognosis. The aim of this study was to present a systematic clinical review of all published cases of TIO. A search was conducted in Pubmed, Embase, Web of Science from inception until April 23rd, 2020. We selected case reports and case series of patients diagnosed with TIO, with information on tumor localization and serum phosphate concentration. Two reviewers independently extracted data on biochemical and clinical characteristics including bone involvement, tumor localization and treatment. 468 articles with 895 unique TIO cases were included. Median age was 46 years (range 9 months-90 years) and 58.3% were males. Hypophosphatemia and inappropriately low or normal 1,25-dihydroxyvitamin D levels, characteristic for TIO, were present in 98% of cases. Median tumor size was 2.7 cm (range 0.5 to 25.0 cm). Serum fibroblast growth factor 23 was related to tumor size (r = 0.344, P < 0.001). In 32% of the cases the tumor was detected by physical examination. Data on bone phenotype confirmed skeletal involvement: 62% of cases with BMD data had a T-score of the lumbar spine ≤ - 2.5 (n = 61/99) and a fracture was reported in at least 39% of all cases (n = 346/895). Diagnostic delay was longer than 2 years in more than 80% of cases. 10% were reported to be malignant at histology. In conclusion, TIO is a debilitating disease characterized by a long diagnostic delay leading to metabolic disturbances and skeletal impairment. Increasing awareness of TIO should decrease its diagnostic delay and the clinical consequences.

Clinical Challenges in Diagnosis, Tumor Localization and Treatment of Tumor-Induced Osteomalacia: Outcome of a Retrospective Surveillance

Tumor-induced osteomalacia (TIO) is an acquired fibroblast growth factor 23 (FGF23)-related hypophosphatemic osteomalacia caused by phosphaturic mesenchymal tumors (PMTs) developed in the bone or soft tissue. Diagnostic delay should be addressed, and ideal techniques to localize PMTs and efficient treatment options should be explored to improve the outcomes of this rare disease. To clarify the detailed clinical course and outcomes of TIO patients, retrospective questionnaire surveys were conducted among physicians from the Japanese Society for Bone and Mineral Research (JSBMR) and the Japan Endocrine Society (JES). The primary survey collected the number of TIO patients between January 2007 and December 2018. The secondary survey aimed to obtain the detailed characteristics, laboratory data, and outcomes. Eighty-eight patients (52 males, mean: 52 years old) were included, and 24 patients were clinically diagnosed with TIO without localized PMTs. The median duration from the onset to detection of high FGF23 levels was 3.4 years, with 77 patients being initially misdiagnosed. Among the methods used to detect small, localized PMTs (≤10 mm), fluorine-18-fluorodeoxyglucose-positron emission tomography/computed tomography and somatostatin receptor scintigraphy were less sensitive than somatostatin receptor positron emission tomography/computed tomography (SRPET/CT). Systemic venous sampling (SVS) of FGF23 was performed in 53 patients; among them, SVS was considered useful for detecting localized PMTs in 45 patients with diverse tumor sizes. Finally, 45 patients achieved biochemical remission by surgery, 39 patients continued pharmaceutical treatment, including burosumab (11 patients), and four patients died. These results encouraged us to further increase the awareness of TIO and to improve the accessibility of SRPET/CT and SVS. Further evidence about the efficacy of new pharmaceutical treatments is awaited. © 2022 American Society for Bone and Mineral Research (ASBMR).

Hypophosphatemia related to a neuro-endocrine tumor of the pancreas: A case report

BACKGROUND

Tumor-induced osteomalacia (TIO) is a paraneoplastic syndrome characterized by hypophosphatemia associated with elevated fibroblast growth factor 23 (FGF23). TIO is primarily caused by benign mesenchymal tumors of the soft tissue and skeleton. Rarely, it is associated with a solid tumor or hematological malignancy. To date, no case of osteomalacia related to pancreatic cancer has been reported in the literature.

CASE REPORT

A 77-year-old woman was admitted to the rheumatology department (RD) of the Clermont-Ferrand University Hospital (France) for further evaluation of her hypophosphatemia. The patient reported bone pain, myalgia, and asthenia. Further laboratory tests revealed hyperphosphaturia, normocalcemia, low serum calcitriol, elevated serum alkaline phosphatase (ALP), and elevated plasma parathyroid hormone (PTH). A renal phosphate depletion disorder was suspected as an etiology for this hypophosphatemia. Finally, FGF23 levels were found to be significantly elevated, leading to a definitive diagnosis of pancreatic neuroendocrine tumor.

CONCLUSION

This is the first report of hypophosphatemic osteomalacia related to pancreatic cancer. Therefore, in the setting of hypophosphatemia associated with renal phosphate wasting and low calcitriol level, plasma FGF23 measurement should be considered.

Diagnosis and surgical treatment of tumor-induced osteomalacia—a literature review and a case report

Background

Tumor-induced osteomalacia (TIO) is a rare condition with fewer than 500 cases reported in the literature although described. Phosphaturic mesenchymal tumor (PMT) is often unrecognized cause of hypophosphatemia. This case report aims to highlight such a rare association which warrants clinical and radiologist attention.

Case

A 51-year-old man had pain in his feet 2 years prior to the most recent presentation in our clinic. The patient experienced increasingly severe body aches and pain, which affected the feet, hips, knees, ribs, waist, and shoulders. MRI and CT led to the diagnosis of multiple insufficiency fractures. Laboratory tests showed that inorganic phosphate (IP) levels had decreased to 0.52 mmol/L(0.81–1.45 mmol/L), while alkaline phosphatase (ALP) had increased to 216 U/L(38.0–126.0 U/L). Positron emission tomography computed tomography showed tumor-derived hypophosphate osteomalacia of the right iliac wing; surgical resection was performed. markers of bone metabolism and bone density returned normal postoperative, after 9 months follow-up.

Conclusion

The possibility of tumor-induced osteomalacia should be considered if unexplained joint pain, decreased bone mineral density, increased ALP and insufficiency fractures, and no similar family history are found in adult patients. Surgical resection of the tumor is the key to the treatment.

The regulation of FGF23 under physiological and pathophysiological conditions

Fibroblast growth factor 23 (FGF23) is an important bone hormone that regulates phosphate homeostasis in the kidney along with active vitamin D (1,25(OH)₂D₃) and parathyroid hormone (PTH). Endocrine effects of FGF23 depend, at least in part, on αKlotho functioning as a co-receptor whereas further paracrine effects in other tissues are αKlotho-independent. Regulation of FGF23 production is complex under both, physiological and pathophysiological conditions. Physiological regulators of FGF23 include, but are not limited to, 1,25(OH)₂D₃, PTH, dietary phosphorus intake, and further intracellular and extracellular factors, kinases, cytokines, and hormones. Moreover, several acute and chronic diseases including chronic kidney disease (CKD) or further cardiovascular disorders are characterized by early rises in the plasma FGF23 level pointing to further mechanisms effective in the regulation of FGF23 under pathophysiological conditions. Therefore, FGF23 also serves as a prognostic marker in several diseases. Our review aims to comprehensively summarize the regulation of FGF23 in health and disease.

The effect of vitamin D supplementation on serum levels of fibroblast growth factor- 23: A systematic review and meta-analysis of randomized controlled trials

Previous studies of the effect of vtamin D on serum levels of fibroblast growth factor- 23 (FGF-23) have yeilded an inconsistent findings. This systematic review and meta-analysis of randomized controlled trials (RCTs) sought to investigate the effect of vitamin D supplementation on serum levels of FGF-23. PubMed, Scopus, ISI Web of Science, and the Cochrane Library were searched, from database inception to November 2020, for RCTs that evaluated the effects of native or active vitamin D supplementation on serum levels of FGF-23 in adults. Weighted mean difference (WMD) were calculated and random effects meta-analysis was used to estimate the overall effects. Twenty-seven trials were included in the meta-analysis. Supplementation with native vitamin D (23 studies, n = 2247 participants; weighted mean difference [WMD] = 0.5 pg/mL, 95 % CI: -0.52 to 1.51, P = 0.33; I² = 29.9 %), and active vitamin D (5 studies, n = 342 participants, WMD = 29.45 pg/mL, 95 % CI: -3.9 to 62.81, P = 0.08; I² = 99.3%) had no significant effects on serum FGF-23 concentration. In subgroup analyses, supplementation with ergocalciferol (3 studies, n = 205 participants; WMD = 18.27 pg/mL, 95 % CI: 5.36-31.17, P = 0.006), and daily dosing regimens (9 studies, n = 1374 participants; WMD = 0.41 pg/mL, 95 % CI: 0.22 to 0.59, P < 0.001) increased serum FGF-23 levels compared to control. Overall, our findings revealed no significan effect of vitamin D supplementation on serum FGF-23 concentration. However, further high quality, large-scale studies are needed to better elucidate this relationship.

Challenges in the management of tumor-induced osteomalacia (TIO)

Tumor-induced osteomalacia (TIO), also known as oncogenic osteomalacia, is a rare acquired paraneoplastic disease, which is challenging to diagnose and treat. TIO is characterized by hypophosphatemia resulting from excess levels of tumor-secreted fibroblast growth factor 23 (FGF23), one of the key physiological regulators of phosphate metabolism. Elevated FGF23 results in renal phosphate wasting and compromised vitamin D activation, ultimately resulting in osteomalacia. Patients typically present with progressive and non-specific symptoms, including bone pain, multiple pathological fractures, and progressive muscle weakness. Diagnosis is often delayed or missed due to the non-specific nature of complaints and lack of disease awareness. Additionally, the disease-causing tumour is often difficult to detect and localize because they are often small, lack localizing symptoms and signs, and dwell in widely variable anatomical locations. Measuring serum/urine phosphate should be an inherent diagnostic component when assessing otherwise unexplained osteomalacia, fractures and weakness. In cases of hypophosphatemia with inappropriate (sustained) phosphaturia and inappropriately normal or frankly low 1,25-dihydroxy vitamin D, differentiation of the potential causes of renal phosphate wasting should include measurement of FGF23, and TIO should be considered. While patients experience severe disability without treatment, complete excision of the tumour is typically curative and results in a dramatic reversal of symptoms. Two additional key current unmet needs in optimizing TIO management are: (1 and 2) the considerable delay in diagnosis and consequent delay between the onset of symptoms and surgical resection; and (2) alternative management. These may be addressed by raising awareness of TIO, and taking into consideration the accessibility and variability of different healthcare infrastructures. By recognizing the challenges associated with the diagnosis and treatment of TIO and by applying a stepwise approach with clear clinical practice guidelines, patient care and outcomes will be improved in the future.

Diagnostic performance of 68Ga-DOTATOC PET/CT in tumor-induced osteomalacia

OBJECTIVE

Tumor-induced osteomalacia (TIO) is caused by typically small tumors that secrete fibroblast growth factor 23 (FGF23). As tumor resection is the only effective treatment for TIO, it is important to detect the culprit tumor. We aimed to assess the utility of 68Gallium-DOTA-D-Phe(1)-Tyr(3)-octreotide (68Ga-DOTATOC) PET/CT in TIO and the correlation between biochemical parameters and the PET/CT results.

METHODS

Thirty-five patients with clinically suspected TIO who had undergone 68Ga-DOTATOC PET/CT were retrospectively analyzed. 68Ga-DOTATOC PET/CT results were compared with biochemical parameters and the final diagnosis, including histopathology.

RESULTS

68Ga-DOTATOC PET/CT detected focal uptake consistent with TIO in 21/35 patients, one of which was considered false positive. In 16 patients, the cause of osteomalacia was confirmed histologically as phosphaturic mesenchymal tumor (n = 15) or fibrous dysplasia (n = 1). The other four patients were judged clinically as true positive by subsequent MRI and the clinical course. Overall, the detection rate of 68Ga-DOTATOC PET/CT was 57% (20/35). Median tumor maximum standardized uptake value (SUVmax) was 6.9 (range 1.5-37.7). There was no significant difference in serum intact FGF23 level between DOTATOC-positive and DOTATOC-negative cases, and no significant correlation was observed between intact FGF23 level and tumor SUVmax.

CONCLUSIONS

68Ga-DOTATOC PET/CT was clinically useful in detecting culprit tumors and subsequent patient management in TIO.

Role of Fibroblast Growth Factor 23 (FGF23) and αKlotho in Cancer

Together with fibroblast growth factors (FGFs) 19 and 21, FGF23 is an endocrine member of the family of FGFs. Mainly secreted by bone cells, FGF23 acts as a hormone on the kidney, stimulating phosphate excretion and suppressing formation of 1,25(OH)₂D₃, active vitamin D. These effects are dependent on transmembrane protein αKlotho, which enhances the binding affinity of FGF23 for FGF receptors (FGFR). Locally produced FGF23 in other tissues including liver or heart exerts further paracrine effects without involvement of αKlotho. Soluble Klotho (sKL) is an endocrine factor that is cleaved off of transmembrane Klotho or generated by alternative splicing and regulates membrane channels, transporters, and intracellular signaling including insulin growth factor 1 (IGF-1) and Wnt pathways, signaling cascades highly relevant for tumor progression. In mice, lack of FGF23 or αKlotho results in derangement of phosphate metabolism and a syndrome of rapid aging with abnormalities affecting most organs and a very short life span. Conversely, overexpression of anti-aging factor αKlotho results in a profound elongation of life span. Accumulating evidence suggests a major role of αKlotho as a tumor suppressor, at least in part by inhibiting IGF-1 and Wnt/β-catenin signaling. Hence, in many malignancies, higher αKlotho expression or activity is associated with a more favorable outcome. Moreover, also FGF23 and phosphate have been revealed to be factors relevant in cancer. FGF23 is particularly significant for those forms of cancer primarily affecting bone (e.g., multiple myeloma) or characterized by bone metastasis. This review summarizes the current knowledge of the significance of FGF23 and αKlotho for tumor cell signaling, biology, and clinically relevant parameters in different forms of cancer.

The Causes of Hypo- and Hyperphosphatemia in Humans

Phosphate homeostasis involves several major organs that are the skeleton, the intestine, the kidney, and parathyroid glands. Major regulators of phosphate homeostasis are parathormone, fibroblast growth factor 23, 1,25-dihydroxyvitamin D, which respond to variations of serum phosphate levels and act to increase or decrease intestinal absorption and renal tubular reabsorption, through the modulation of expression of transcellular transporters at the intestinal and/or renal tubular level. Any acquired or genetic dysfunction in these major organs or regulators may induce hypo- or hyperphosphatemia. The causes of hypo- and hyperphosphatemia are numerous. This review develops the main causes of acquired and genetic hypo- and hyperphosphatemia.

Association between shift work and biological factors including FGF-23, klotho, and serum 25-(OH) vitamin D3 among Korean firefighters: a cross-sectional study

STUDY OBJECTIVES

Shift work is known to be detrimental to an individual's health as it disrupts the circadian rhythm and is a risk factor for cancer. It has been reported that elevated fibroblast growth factor (FGF)-23, increased serum soluble α-klotho, and decreased vitamin D3 are associated with cancer progression. We studied the relationship between shift work and the levels of FGF-23, α-klotho, and vitamin D3 amongst firefighters, as they work in long shifts outside the traditional daytime schedule.

METHODS

The study consisted of 450 participants who were firefighters. We measured FGF-23, α-klotho, and vitamin D3 levels in their blood and a set of questionnaires were given to the participants to evaluate their health habits. After determining and adjusting for potential confounding factors, we compared the levels of FGF-23, α-klotho, and serum vitamin D3 by job and shift types.

RESULTS

FGF-23 and α-klotho levels were significantly higher in shift workers than traditional day workers, and in 3-day cycle shift workers than workers with another shift schedule. When the levels of these substances were compared based on different types of jobs, firefighters had a lower level of vitamin D3. We conclude that shift work is positively correlated with the levels of FGF-23 and α-klotho.

CONCLUSIONS

Levels of FGF-23 and α-klotho were linked to shift work and job types. Although vitamin levels did not differ by shift types, vitamin D3 levels were lower in firefighters. These findings suggest that high levels of FGF-23 and α-klotho are potential risk factors for cancer among firefighters.

Elevated FGF23 in a patient with hypophosphatemic osteomalacia associated with neurofibromatosis type 1

CONTEXT

The mechanism behind hypophosphatemia in the setting of neurofibromatosis type 1 (NF1) is not known. We describe a possible role of fibroblast growth factor-23 (FGF23) in the pathophysiology of hypophosphatemia in a patient with NF1.

CASE DESCRIPTION

A 34-year woman with NF1 presented with severe hypophosphatemia, osteomalacia, and elevated plasma FGF23. The patient had considerable improvement on replacement of oral phosphate. Two Ga68 DOTANOC PET-CT scans over a period of 2 years failed to detect any localized uptake. Immuno-staining for FGF23 was absent in the neural-derived tumour cells of the neurofibromas in the proband.

CONCLUSION

The patient with NF1 had elevated circulating FGF23. Tumour cells in the neurofibroma tissues did not stain for FGF23 on IHC. It is unlikely for neurofibromas to contribute to high circulating FGF23 levels in the proband.

Metastatic prostate cancer presenting as tumour-induced osteomalacia

Tumour-induced osteomalacia (TIO), or oncogenic osteomalacia, is a paraneoplastic syndrome marked by hypophosphataemia, renal phosphate wasting, bone pain, weakness, and fractures. The syndrome has been reported with both benign and malignant tumours including parotid gland basal cell tumours, thyroid carcinomas, colon adenocarcinomas, and prostate cancer. Often, the syndrome is marked by an insidious course during which patients present with generalised bony pain and weakness, which do not resolve until the underlying tumour is identified and treated. We present a case of a patient with Parkinson's disease whose subacute weakness, lower extremity paresis, and renal phosphate wasting led to the synchronous diagnosis of metastatic prostate adenocarcinoma and TIO.

Fibroblast Growth Factor 23 and Klotho in AKI

Acute kidney injury (AKI) is associated with many of the same mineral metabolite abnormalities that are observed in chronic kidney disease. These include increased circulating levels of the osteocyte-derived, vitamin D-regulating hormone, fibroblast growth factor 23 (FGF23), and decreased renal expression of klotho, the co-receptor for FGF23. Recent data have indicated that increased FGF23 and decreased klotho levels in the blood and urine could serve as novel predictive biomarkers of incident AKI, or as novel prognostic biomarkers of adverse outcomes in patients with established AKI. In addition, because FGF23 and klotho exert numerous classic as well as off-target effects on a variety of organ systems, targeting their dysregulation in AKI may represent a unique opportunity for therapeutic intervention. We review the pathophysiology, kinetics, and regulation of FGF23 and klotho in animal and human studies of AKI, and we discuss the challenges and opportunities involved in targeting FGF23 and klotho therapeutically.

Nephrocalcinosis and Nephrolithiasis in X-Linked Hypophosphatemic Rickets: Diagnostic Imaging and Risk Factors

Context

Nephrocalcinosis (NC) and nephrolithiasis (NL) are described in hypophosphatemic rickets, but data regarding their prevalence rates and the presence of metabolic risk factors in X-linked hypophosphatemic rickets (XLH) are scarce.

Objective

To determine the prevalence rates of NC and NL and their risk factors in patients with XLH with confirmed PHEX mutations.

Methods

Renal ultrasonography (US) and CT were performed in 16 children and 23 adults. The images were evaluated by two blinded radiologists specializing in US and two specializing in CT. Confirmation of NC was determined with a positive result on both US and CT, whereas the diagnosis of NL was confirmed by CT alone. The presence of hypercalciuria, hypocitraturia, and hyperoxaluria was determined from 24-hour urinary samples from each patient. The glomerular filtration rate was estimated.

Results

NC was identified in 15 patients (38.4%), and stratification by age group showed a higher prevalence of NC in children than in adults (56.2% vs 26.1%). CT identified NL in four adults (10.2%). Patients in the pediatric group required intensive use of phosphate, started treatment earlier, and presented greater phosphaturia than those in the adult group (P < 0.01). In addition to hyperphosphaturia, which was present in all patients with XLH, hypocitraturia was the most common metabolic factor (28.2%), whereas hypercalciuria occurred in two patients (5.1%). None had hyperoxaluria. Most patients had normal renal function.

Conclusions

NC was more prevalent than NL. The main metabolic factor was hyperphosphaturia, and intensive phosphate treatment appears to be a worsening factor for kidney calcification.

Oncogenic osteomalacia and metastatic breast cancer: a case report and review of the literature

Objectives

Oncogenic osteomalacia is a rare paraneoplastic metabolic syndrome that is characterised by severe hypophosphataemia, hyperphosphaturia and osteomalacia secondary to renal loss of phosphate. It is commonly caused by overproduction of fibroblast growth factor-23 (FGF23) from benign tumours of mesenchymal origin. Currently, there is no clear evidence on the management of oncogenic osteomalacia in patients with metastatic solid tumours.

Methods

We report a case of breast cancer-induced oncogenic osteomalacia and discuss its diagnosis and management.

Results

A 71-year-old woman with advanced breast cancer developed symptomatic oncogenic osteomalacia with raised FGF23, severe hypophosphataemia and hypocalcaemia. The electrolytic disturbances were exacerbated after the administration of bisphosphonates in the context of her oncological treatment. Systemic chemotherapy and maintenance endocrine treatment along with phosphate and calcium supplementation reduced the activity of oncogenic osteomalacia and resolved the electrolytic imbalances.

Conclusions

To our knowledge, this is the first reported case of oncogenic osteomalacia in a patient with breast cancer. Oncogenic osteomalacia constitutes a diagnostic and therapeutic challenge. Pre-clinical and clinical evidence suggest that a possible underlying mechanism is the presence of molecular alterations in the FGF/FGFR signalling pathway leading to overexpression of FGF23. In metastatic setting, anticancer treatment can potentially lead to the normalisation of the electrolytic disturbances and reduction of the activity of oncogenic osteomalacia. The use of antiresorptive therapy in patients with bone metastases can potentially trigger FGF23 overexpression. Its use should be guided by the patients' risk of skeletal-related events and electrolytic disturbances as well as the degree of activity of oncogenic osteomalacia.

Paraneoplastic syndromes and other systemic disorders associated with neuroendocrine neoplasms

Neuroendocrine paraneoplastic syndromes (PNS) consist of metabolic disorders that accompany benign and malignant neoplasms but remain unrelated to mass effects or invasion by the primary tumor or its metastases. The underlying pathogenesis responsible for PNS usual clinical presentation relies on aberrant production of protein hormones, proteins and other substances by the tumor. Prompt recognition of characteristic signs and symptoms combined with serological identification of key substances may result in early diagnosis of PNS and its underlying malignancy. For these reasons, healthcare professionals should familiarize themselves with tumor-induced hypercalcemia, syndrome of inappropriate antidiuretic hormone, carcinoid syndrome, virilisation syndrome, gynecomastia, acromegaly, Cushing syndrome, osteogenic osteomalacia, tumor-induced hypoglycemia, necrolytic migratory erythema, and watery diarrhea, hypokalemia and achlorydria syndrome. Medical awareness for PNS can improve patient outcomes through earlier administration of cancer therapy and treatment, better symptomatic relief and prolong overall survival.

Varied presentation of sinonasal phosphaturic mesenchymal tumour: report of a case series with follow-up

PURPOSE

Phosphaturic mesenchymal tumour (PMT) of the paranasal sinuses is a rare tumour that is associated with oncogenous osteomalacia causing predominant musculoskeletal symptoms. We present a series of eight patients diagnosed to have PMT of the paranasal sinuses with varied presentation and highlight the appropriate evaluation required to arrive at the diagnosis.

METHODS

Retrospective review of eight patients diagnosed to have PMT-causing tumour-induced osteomalacia with follow-up data.

RESULTS

Eight patients, 4 males and 4 females, aged 36-67 years (mean = 44 years) presented with vague musculoskeletal symptoms (6 patients) or epistaxis (3 patients). Six patients were found to have hypophosphatemia, phosphaturia and raised FGF-23 levels preoperatively. All eight patients were found to have a tumour in the nose and/ paranasal sinuses with one patient having intracranial extension. All patients were treated with endoscopic excision of these tumours which resulted in resolution of symptoms and normalisation of biochemical abnormalities. In addition, one patient required a craniofacial resection. Histopathological features were consistent with PMT mixed connective tissue variant. Two atypical patients were seen. The longest follow-up was for 5 years and there was no evidence of recurrence during the follow-up period in any patient.

CONCLUSION

Diagnosis of PMT of the paranasal sinuses causing oncogenous osteomalacia requires a high index of suspicion when there are no ENT symptoms. Appropriate biochemical tests and histopathology lead to the correct diagnosis. Total endoscopic surgical excision leads to a good outcome.

Ectopic expression of Klotho in fibroblast growth factor 23 (FGF23)-producing tumors that cause tumor-induced rickets/osteomalacia (TIO)

Tumor-induced rickets/osteomalacia (TIO) is a rare paraneoplastic syndrome caused by tumors that ectopically express fibroblast growth factor 23 (FGF23). FGF23 is a bone-derived hormone that regulates serum phosphate concentrations. Patients with TIO develop hypophosphatemic rickets/osteomalacia due to FGF23 excess and suffer from symptoms such as leg deformities, bone pain, skeletal muscle myopathy, and multiple fractures/pseudofractures. Usually, successful surgical removal of the causative tumors normalizes serum FGF23 and phosphate concentrations in patients with TIO. Most FGF23-producing tumors associated with TIO are histologically called phosphaturic mesenchymal tumor, mixed connective tissue variant (PMTMCT). The precise mechanism by which these tumors ectopically overproduce FGF23 outside of bone is yet to be clarified. Therefore, we performed an RNA sequencing analysis of a PMTMCT that was found in the left parotid gland of a patient with TIO. Among the upregulated genes, we focused on Klotho, the protein product of which is a single pass transmembrane protein that works along with an FGF receptor 1c as a receptor complex for FGF23. Subsequent histological analysis confirmed the ectopic expression of Klotho in other PMTMCTs. From these results, we assume that the ectopic expression of Klotho in PTMMCTs enables a positive feedback loop in FGF23 production via the activation of FGF receptor 1c and exacerbates disease manifestations in TIO.

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Klotho is ectopically expressed in the FGF23-producing mesenchymal tumors.

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Klotho enables the activation of the FGFR signaling pathway in PMTMCTs.

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Klotho enables the autocrine/paracrine effects of FGF23 in PMTMCTs.

Tumor-induced osteomalacia

Tumor-induced osteomalacia (TIO), also known as oncogenic osteomalacia, is a rare paraneoplastic syndrome characterized by hypophosphatemia resulting from decreased tubular phosphate reabsorption, with a low or inappropriately normal level of active vitamin D. The culprit tumors of TIO could produce fibroblast growth factor 23 which plays a role in regulating renal Pi handling and 25-hydroxyvitamin D 1α-hydroxylase activity. Chronic hypophosphatemia could eventually lead to inadequate bone mineralization, presenting as osteomalacia. The diagnosis should be considered when patients manifest as hypophosphatemia and osteomalacia, or rickets and needs to be differentiated from other disorders of phosphate metabolism, such as the inhereditary diseases like X-linked hypophosphataemic rickets, autosomal dominant hypophosphataemic rickets, autosomal recessive hypophosphataemic rickets and acquired diseases like vitamin D deficiency. Localization of responsible tumors could be rather difficult since the vast majority are very small and could be everywhere in the body. A combination of thorough physical examination, laboratory tests and imaging techniques should be applied and sometimes a venous sampling may come into handy. The technology of somatostatin-receptor functional scintigraphy markedly facilitates the localization of TIO tumor. Patients undergoing complete removal of the causative neoplasm generally have favorable prognoses while a few have been reported to suffer from recurrence and metastasis. For those undetectable or unresectable cases, phosphate supplements and active vitamin D should be administrated and curative intended radiotherapy or ablation is optional.

Phosphaturic mesenchymal tumors: what an endocrinologist should know

Tumor-induced osteomalacia (TIO), also known as "oncogenic osteomalacia", is a rare cause of osteomalacia. TIO often has an insidious onset characterized clinically by progressive muscle weakness and bone pain with fractures. The hallmark biochemical finding is a persistent low serum phosphorus concentration due to renal phosphate wasting. The vast majority of cases of TIO result from production of the phosphaturic hormone fibroblast growth factor 23 (FGF23) by a histologically distinctive mesenchymal tumor, termed "phosphaturic mesenchymal tumor" (PMT). Circulating FGF23 induces internalization of renal sodium/phosphate co-transporters resulting in reduced proximal tubular phosphate reabsorption. FGF23 also inhibits production of 1α,25-dihydroxyvitamin D which is inappropriately low or normal in the context of hypophosphatemia. Diagnosis is often delayed owing to the rarity of the condition and an underappreciation for the role of phosphorus as a cause for the constellation of symptoms. Primary treatment for TIO is identification of the offending tumor and surgical removal. However, these tumors are notoriously difficult to find, precluding the opportunity for a curative surgery in many. In such cases, phosphate and calcitriol therapy is used to improve symptoms and heal the osteomalacia. Recently, molecular genetic studies have shown recurrent genetic events in PMT, including the novel fusions FN1-FGFR1 and less commonly FN1-FGF1. These fusion events are hypothesized to result in autocrine/paracrine signaling loops within the tumor, spurring tumorigenesis. This review will cover the clinical features, imaging characteristics, pathologic features, molecular genetic aspects, and therapy of PMT, with a brief discussion of other neoplasms that may cause TIO.

X-Linked Hypophosphatemia and FGF23-Related Hypophosphatemic Diseases: Prospect for New Treatment

Phosphate plays essential roles in many biological processes, and the serum phosphate level is tightly controlled. Chronic hypophosphatemia causes impaired mineralization of the bone matrix and results in rickets and osteomalacia. Fibroblast growth factor 23 (FGF23) is a bone-derived hormone that regulates phosphate metabolism. FGF23 excess induces hypophosphatemia via impaired phosphate reabsorption in the renal proximal tubules and decreased phosphate absorption in the intestines. There are several types of genetic and acquired FGF23-related hypophosphatemic diseases. Among these diseases, X-linked hypophosphatemia (XLH), which is caused by inactivating mutations in the phosphate-regulating endopeptidase homolog, X-linked (PHEX) gene, is the most prevalent form of genetic FGF23-related hypophosphatemic rickets. Another clinically relevant form of FGF23-related hypophosphatemic disease is tumor-induced osteomalacia (TIO), a paraneoplastic syndrome associated with FGF23-producing tumors. A combination of active vitamin D and phosphate salts is the current medical therapy used to treat patients with XLH and inoperative TIO. However, this therapy has certain efficacy- and safety-associated limitations. Several measures to inhibit FGF23 activity have been considered as possible new treatments for FGF23-related hypophosphatemic diseases. In particular, a humanized monoclonal antibody for FGF23 (burosumab) is a promising treatment in patients with XLH and TIO. This review will focus on the phosphate metabolism and the pathogenesis and treatment of FGF23-related hypophosphatemic diseases.

Multiple faces of fibroblast growth factor-23

PURPOSE OF REVIEW

This review examines the role of fibroblast growth factor-23 (FGF-23) in mineral metabolism, innate immunity and adverse cardiovascular outcomes.

RECENT FINDINGS

FGF-23, produced by osteocytes in bone, activates FGFR/α-Klotho (α-Kl) complexes in the kidney. The resulting bone-kidney axis coordinates renal phosphate reabsorption with bone mineralization, and creates a counter-regulatory feedback loop to prevent vitamin D toxicity. FGF-23 acts to counter-regulate the effects of vitamin D on innate immunity and cardiovascular responses. FGF-23 is ectopically expressed along with α-Kl in activated macrophages, creating a proinflammatory paracrine signaling pathway that counters the antiinflammatory actions of vitamin D. FGF-23 also inhibits angiotensin-converting enzyme 2 expression and increases sodium reabsorption in the kidney, leading to hypertension and left ventricular hypertrophy. Finally, FGF-23 is purported to cause adverse cardiac and impair neutrophil responses through activation of FGFRs in the absence of α-Kl. Although secreted forms of α-Kl have FGF-23 independent effects, the possibility of α-Kl independent effects of FGF-23 is controversial and requires additional experimental validation.

SUMMARY

FGF-23 participates in a bone-kidney axis regulating mineral homeostasis, proinflammatory paracrine macrophage signaling pathways, and in a bone-cardio-renal axis regulating hemodynamics that counteract the effects of vitamin D.

The Foot That Broke Both Hips: A Case Report and Literature Review of Tumor-Induced Osteomalacia

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by hypophosphatemia and clinical symptoms of osteomalacia. Only discussed as case reports, there is still limited knowledge of this condition as a potentially curable cause of osteomalacia among clinicians and pathologists. In this article, we present a case of tumor-induced osteomalacia in a 59-year-old gentleman followed by an up-to-date review of the existing literature on TIO.

Tumour-induced osteomalacia

Tumour-induced osteomalacia (TIO), also known as oncogenic osteomalacia, is a rare paraneoplastic disorder caused by tumours that secrete fibroblast growth factor 23 (FGF23). Owing to the role of FGF23 in renal phosphate handling and vitamin D synthesis, TIO is characterized by decreased renal tubular reabsorption of phosphate, by hypophosphataemia and by low levels of active vitamin D. Chronic hypophosphataemia ultimately results in osteomalacia (that is, inadequate bone mineralization). The diagnosis of TIO is usually suspected when serum phosphate levels are chronically low in the setting of bone pain, fragility fractures and muscle weakness. Locating the offending tumour can be very difficult, as the tumour is often very small and can be anywhere in the body. Surgical removal of the tumour is the only definitive treatment. When the tumour cannot be located or when complete resection is not possible, medical treatment with phosphate salts or active vitamin D is necessary. One of the most promising emerging treatments for unresectable tumours that cause TIO is the anti-FGF23 monoclonal antibody KRN23. The recent identification of a fusion of fibronectin and fibroblast growth factor receptor 1 (FGFR1) as a molecular driver in some tumours not only sheds light on the pathophysiology of TIO but also opens the door to a better understanding of the transcription, translocation, post-translational modification and secretion of FGF23, as well as suggesting approaches to targeted therapy. Further study will reveal if the FGFR1 pathway is also involved in tumours that do not harbour the translocation.

Paraneoplastic endocrine syndromes

The majority of neoplasms are responsible for symptoms caused by mass effects to surrounding tissues and/or through the development of metastases. However, occasionally neoplasms, with or without endocrine differentiation, acquire the ability to secrete a variety of bioactive substances or induce immune cross-reactivity with the normal tissues that can lead to the development of characteristic clinical syndromes. These syndromes are named endocrine paraneoplastic syndromes when the specific secretory components (hormones, peptides or cytokines) are unrelated to the anticipated tissue or organ of origin. Endocrine paraneoplastic syndromes can complicate the patient's clinical course, response to treatment, impact prognosis and even be confused as metastatic spread. These syndromes can precede, occur concomitantly or present at a later stage of tumour development, and along with the secreted substances constitute the biological 'fingerprint' of the tumour. Their detection can facilitate early diagnosis of the underlying neoplasia, monitor response to treatment and/or detect early recurrences following successful initial management. Although when associated with tumours of low malignant potential they usually do not affect long-term outcome, in cases of highly malignant tumours, endocrine paraneoplastic syndromes are usually associated with poorer survival outcomes. Recent medical advances have not only improved our understanding of paraneoplastic syndrome pathogenesis in general but also enhanced their diagnosis and treatment. Yet, given the rarity of endocrine paraneoplastic syndromes, there is a paucity of prospective clinical trials to guide management. The development of well-designed prospective multicentre trials remains a priority in the field in order to fully characterise these syndromes and provide evidence-based diagnostic and therapeutic protocols.

Evaluation of bone mineral density and microarchitectural parameters by DXA and HR-pQCT in 37 children and adults with X-linked hypophosphatemic rickets

In X-linked hypophosphatemic (XLH) rickets, dual-energy X-ray absorptiometry (DXA) measurements must be analyzed with caution. High-resolution peripheral quantitative computed tomography (HR-pQCT) analysis suggested that XLH primarily affects the cancellous compartment, with the tibia more affected than the radius. Effective treatment of XLH appears to positively affect bone mineralization, mainly in the bone cortex.

INTRODUCTION

The purpose of this study is to evaluate bone mineral density (BMD) and microarchitecture in 37 patients (13 children and 24 adults) with XLH confirmed by PHEX mutations from a tertiary center compared to healthy controls.

METHODS

Areal BMD (aBMD) was evaluated by DXA, whereas volumetric BMD (vBMD) and microarchitectural parameters were analyzed by HR-pQCT.

RESULTS

Adult XLH patients had higher lumbar aBMD (p < 0.01) than the controls. At the radius, the vBMD was similar between XLH patients and controls. At the tibia, XLH patients had lower total vBMD (p = 0.04), likely resulting from decreased trabecular vBMD (p < 0.01), and this difference was observed in the children and adult groups. Analysis based on metabolic status showed that the adult XLH patients with non-compensated disease had lower cortical vBMD at the tibia than the compensated XLH patients (p = 0.03). The microarchitectural differences at the radius and tibia included lower trabecular number (p < 0.01), greater trabecular separation (p < 0.01), and higher trabecular network inhomogeneity (p < 0.01) in XLH patients compared to their controls. At the radius, adults exhibited greater trabecular deficits than were seen in children.

CONCLUSIONS

In XLH patients, DXA measurements must be analyzed with caution due to the interference of anatomic and anthropometric factors. HR-pQCT analysis suggested that XLH primarily affects the cancellous compartment, with the tibia more affected than the radius. Effective treatment of XLH appears to positively affect bone mineralization, mainly in the bone cortex.

Fibroblast Growth Factor 23-Mediated Bone Disease

Fibroblast growth factor 23 (FGF23) is an important regulator of phosphate and vitamin D metabolism and its excessive or insufficient production leads to a wide variety of skeletal disorders. This article reviews the FGF23-α-Klotho signaling pathway, highlighting the latest developments in FGF23 regulation and action, and describes the disorders associated with FGF23 excess or deficiency.

Tumor-induced Osteomalacia Caused by a Parotid Tumor

A 77-year-old man was suspected of having tumor-induced osteomalacia (TIO) because of hypophosphatemia (1.9 mg/dL) and elevated serum fibroblast growth factor 23 (FGF23) level (186.9 pg/mL). We detected a tumor in his left parotid gland, and the FGF23 level in the left external jugular vein indicated that the tumor overproduced FGF23. After the removal of the tumor, the serum FGF23 level rapidly decreased, and the serum phosphate normalized. This is the first case of TIO caused by a tumor in a parotid gland. This case indicates that the responsible tumors for TIO can be quite diverse.

Tumour-induced Osteomalacia Secondary to a Sarcoma

Tumour-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.

Hypophosphataemia due to FGF-23 producing B cell non-Hodgkin's lymphoma

Oncogenic osteomalacia (or tumour-induced osteomalacia) is a rare paraneoplastic syndrome caused by overproduction of fibroblastic growth factor 23 (FGF-23) by tumours. Excessive production of FGF-23 can lead to severe, symptomatic hypophosphataemia. The majority of cases have been associated with benign tumours of bone or soft tissue, such as haemangiopericytomas or other neoplasms of mesenchymal origin. We present a case of a 68-year-old woman with an FGF-23 producing B cell non-Hodgkin's lymphoma. Treatment with immunochemotherapy resulted in normalisation of serum FGF-23 and phosphate levels.

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.

Tumour-induced osteomalacia: a literature review and a case report

Tumour-induced osteomalacia (TIO) is a rare paraneoplastic syndrome characterised by severe hypophosphataemia and osteomalacia, with renal phosphate wasting that occurs in association with tumour. The epidemiology likewise aetiology is not known. The clinical presentation of TIO includes bone fractures, bone and muscular pains, and sometimes height and weight loss. TIO may be associated with mesenchymal tumours which may be benign or malignant in rare cases. Mesenchymal tumour itself may be related to fibroblast growth factor 23 (FGF23), which is responsible for hypophosphataemia and phosphaturia occurring in this paraneoplastic syndrome. Hypophosphataemia, phosphaturia and elevated alkaline phosphatase are the main laboratory readings that may lead to more precise investigations and better diagnosis. Finding the tumour can be a major diagnostic challenge and may involve total body magnetic resonance imaging, computed tomography and scintigraphy using radiolabelled somatostatin analogue. The treatment of choice for TIO is resection of a tumour with a wide margin to insure complete tumour removal, as recurrences of these tumours have been reported. We provide here an overview on the current available TIO case reports and review the best practices that may lead to earlier recognition of TIO and the subsequent treatment thereof, even though biochemical background and the long-term prognosis of the disease are not well understood. This review also includes a 4-year-long history of a patient that featured muscular pains, weakness and multiple stress fractures localised in the hips and vertebra with subsequent recovery after tumour resection. Because the occurrence of such a condition is rare, it may take years to correctly diagnose the disease, as is reported in this case report.

Changes of erythrocyte element status of colectomysed cancerous patients: Retrospective study

Nowadays it has been established that metals and metal-induced oxidative stress act on signal transduction pathways, and are in association with cancer growth and spreading as well as in neurodegenerative disorders. In cases of several neurodegenerative diseases metals, especially Al, can be considered as a risk factor. Frequency of chemotherapy-related cognitive impairment or "chemobrain" is mentioned to be significant in literature, although very little is known about the chemotherapy-caused chemobrain and its connection with metal homeostasis alteration. Dysregulation of metal homeostasis can be assumed as one of the key factors in the progression of neurodegeneration. Therefore we were interested in studying metal element status of 27 adult patients in 3 years after their colectomy, 22 outpatients and 10 healthy volunteers in both genders. Tumour markers, laboratory parameters and metal element concentrations were determined. We found significant difference among the Al concentrations in operated patients compared with controls. Redox active Fe and Cu levels were also elevated slightly in this patient group. P and S concentrations changed in different ways, and Ca levels were slightly lower, than in healthy controls. Because of all above mentioned, examination of metal homeostasis in cancerous patients is necessary to moderate the risk of chemobrain and other redox-related disorders.

FGF23-Associated Tumor-Induced Osteomalacia in a Patient With Small Cell Carcinoma: A Case Report and Regulatory Mechanism Study

Tumor-induced osteomalacia (TIO) is typically caused by phosphaturic mesenchymal tumor (PMT) that secretes the phosphaturic hormone, fibroblast growth factor-23 (FGF23), resulting in decreased phosphate reabsorption in kidneys, hypophosphatemia, and finally osteomalacia. Rare cases of malignant tumor manifesting with TIO other than PMT had been reported, although in most of these reports, except one, circulating FGF23 levels were not evaluated and tissue expressing of FGF23 was not confirmed. In this article, we report a case of TIO in a patient with pulmonary small cell carcinoma with liver metastasis. The patient manifested with hypophosphatemia. His circulating level of FGF23 was markedly increased. The expression of FGF23 in tumor cells was confirmed. Furthermore, the regulatory mechanism of FGF23 in this patient was also investigated.

Phosphaturic mesenchymal tumors. Survey of 8 cases from a single Mexican medical institution

Phosphaturic mesenchymal tumor (PMT) is a morphologically heterogeneous soft tissue and bone neoplasm, producing a paraneoplastic syndrome due to phosphate wasting. These tumors produce fibroblast growth factor 23, which is implicated in renal tubule phosphate loss. Medical records of patients seen from 1999 to 2013 with osteomalacia associated or not with a tumor were reviewed. Clinical and laboratory data, radiographic studies, and follow-up of 8 patients were tabulated. Histologic features and the immunoprofile of the tumors were analyzed. There were 208 patients with osteomalacia, but only 8 (3.84%) had osteomalacia associated with a tumor. The median age of the patients was 40 years. The tumor size ranged from 1.5 to 4 cm. Five were located in soft tissues and skin; and 3, in bones. Osteomalacia symptoms lasted from 2 to 14 years with a median of 6 years. Laboratory data showed hypophosphatemia and phosphaturia in all patients. All tumors were histologically benign. Histologically, the salient features were a hemangiopericytoid pattern, chronic hemorrhage, and microcystic areas. All neoplasms were diffusely positive for vimentin and focally positive for epithelial membrane antigen, CD34, and S-100 protein. Ki-67 was positive in approximately 10% of neoplastic cells in 2 cases and less than 1% in the remainder. We report 8 cases of PMTs producing osteomalacia, from a single third-level Mexican medical institution. These tumors occurred in soft tissues, skin, and bones. All tumors were benign, small, not easily detected by physical examination and diagnosed due to the metabolic abnormalities.

A novel chromogenic in situ hybridization assay for FGF23 mRNA in phosphaturic mesenchymal tumors

Phosphaturic mesenchymal tumors of the mixed connective tissue type (PMT) are very rare tumors of bone and soft tissues. Most patients with PMT have long-standing osteomalacia secondary to production of fibroblast growth factor 23 (FGF23), a hormone that inhibits phosphate reuptake within the renal proximal tubule. Previously, we have reported the detection of FGF23 mRNA in PMT by reverse transcription polymerase chain reaction (PCR); however, the low specificity and risk for nontumoral tissue contamination inherent in PCR-based methodology limit its clinical utility. We evaluated RNAscope as a semiquantitative method of in situ FGF23 mRNA detection in the diagnosis of PMT. Twenty-five PMTs (median 52 y, range 5 to 73 y) occurred in patients with tumor-induced osteomalacia (TIO), manifesting as masses (mean 3.9 cm, range 1.4 to 12 cm) in various bones and soft tissues. FGF23 mRNA was positive in 96% (22/23) informative cases of PMT: 16 cases scored 3+; 5 scored as 2+; 1 scored as 1+. Among these cases, FGF23 mRNA was detected in 3 malignant PMTs along with their metastases. Forty control cases included aneurysmal bone cyst (N=4), chondromyxoid fibroma (N=8), high-grade osteosarcomas (N=8), and (nonfamilial) tumoral calcinosis, as well as miscellaneous cartilage-forming tumors or osteoid-forming tumors and soft tissue tumors. All control cases were negative for FGF23 mRNA in the lesional cells. One aneurysmal bone cyst had rare FGF23 mRNA-expressing osteocytes clustered around remodeled bone. One ovarian serous carcinoma in a patient with disseminated disease, elevated serum FGF23, and TIO was negative for FGF23 mRNA in the neoplastic cells. We conclude that RNAscope is a highly sensitive and specific, semiquantitative in situ hybridization method of FGF23 mRNA detection applicable to formalin-fixed, paraffin-embedded tissues. Detection of FGF23 expression is a valuable diagnostic adjunct, especially in patients with occult TIO. Compared with reverse transcription PCR, this method preserves tissue morphology and reduces "false positives" related to detection of endogenous FGF23 mRNA expression by osteocytes.