Successful Management Of Tumor-Induced Osteomalacia with Radiofrequency Ablation: A Case Series

Phosphaturic mesenchymal tumor: management and outcomes of ten patients treated at a single institution

BACKGROUND

Phosphaturic mesenchymal tumor (PMT) is a rare tumor that causes tumor-induced osteomalacia. Patients present with non-specific symptoms secondary to renal phosphate wasting and decreased bone mineralization. We sought to assess: (1) What are the common presenting features, laboratory and imaging findings, histologic findings of phosphaturic mesenchymal tumors? (2) What are the available treatment strategies for phosphaturic mesenchymal tumors and their long-term outcomes in terms of local recurrence and symptom control after treatment?

METHODS

We retrospectively identified patients with a histologic diagnosis of PMT located in the axial or appendicular skeleton, or surrounding soft tissues. A total of 10 patients were finally included in our study.

RESULTS

Median tumor size was 1.9 cm (range, 1.1 to 6.1) and median time from symptom onset to diagnosis was 3 years (range, 0.5 to 15 years). All patients but one presented with hypophosphatemia (median 1.9 mg/dL, range 1.2 to 3.2). Pre-operative FGF-23 was elevated in all cases (median 423.5 RU/mL, range 235 to 8950). Six patients underwent surgical resection, three were treated percutaneously (radiofrequency ablation or cryoablation), and one refused treatment. Only one patient developed local recurrence and no patients developed metastatic disease. At last follow-up, nine patients showed no evidence of disease and one was alive with disease.

CONCLUSION

Phosphaturic mesenchymal tumor is a rare tumor presenting with non-specific symptoms. Surgery is the standard treatment when negative margins can be achieved without significant morbidity. In patients with small tumors in surgically-inaccessible areas, radiofrequency ablation or cryoablation can be performed successfully.

Intracranial Phosphaturic Mesenchymal Tumors: A Systematic Literature Review of a Rare Entity

BACKGROUND

Phosphaturic Mesenchymal Tumors (PMTs) are rare mesenchymal neoplasms known for producing Tumor-induced Osteomalacia (TIO). TIO is an uncommon paraneoplastic syndrome characterized by radiographic evidence of inadequate bone mineralization and analytical abnormalites.

METHODS

We sought to present a case of TIO caused by skull base PMT with intracranial extension, manifesting with pain, progressive weakness, and multiple bone fractures. Furthermore, a systematic review was performed, following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines. A search was conducted in PubMed database with title/abstract keywords "Phosphaturic mesenchymal tumor" and "Osteomalacia." Search results were reviewed looking for intracranial or skull base tumors.

RESULTS

Our systematic review included 29 reported cases of intracranial PMT. In the reviewed cases there was a significative female predominance with 22 cases (75,86%). Osteomalacia was presented in 25 cases (86,20%). Bone fractures were present in 10 cases (34,48%). The most common site of involvement was the anterior cranial fossa in 14 cases (48,27%). Surgery was performed in 27 cases (93,10%) with previous tumor embolization in 4 cases (13,79%). Total recovery of the presenting symptoms in the first year was achieved in 21 cases (72,41%). Recurrence of the disease was described in 6 cases (25%).

CONCLUSIONS

Skull base PMTs with intracranial extension are extremely rare tumors. Most patients are middle-aged adults with a PMT predominantly located in anterior cranial fossa. Surgery is the current treatment of choice with optimal outcome at 1-year follow-up, although recurrence could be present in almost 25% of the cases.

Long-Term Follow-Up Data of Tumor-Induced Osteomalacia Managed with Surgery and/or Radiofrequency Ablation from a Single Center

Data on radiofrequency ablation (RFA) in tumor-induced osteomalacia (TIO) are restricted to case reports (~ 11 patients) and long-term follow-up data are further scarce. We describe our experience on managing TIO from a tertiary care center in India. Retrospective study of patients with localized TIO was performed and clinical, biochemical, treatment and follow-up details were retrieved. Normalization of serum phosphorus in absence of phosphate supplementation was defined as remission. Of 33 patients (23 males), 24 patients underwent surgery as first-line treatment, and early remission, delayed remission (> 1 month for phosphorus normalization) and persistence were observed 12, 3, and 9 patients at a median follow-up of 5 (4-9) years. The gender, age, tumor size, location of tumors and FGF23 levels were not statistically different in patients who were in remission after surgery versus those with persistent disease. Second/third line treatment included conventional medical treatment and/or repeat surgery (n = 3), radiotherapy (n = 3), peptide receptor radionuclide therapy (n = 1), RFA (n = 1). Two patients had transient worsening (weeks) of weakness post-surgery. 10 patients underwent RFA (first-line n = 9); at the last follow-up 5 (4-10) years, 7 are in remission. Two of three persistent disease patients had large tumors (5.6 and 3.6 cm). There were no RFA-related complications except local ulcer in one. Although persistent disease was present in a few patients in both arms, there was no recurrence in either RFA or surgical cohort. RFA provide durable response similar to surgery, persistence requires multi-modality treatment.

Orthopedic Surgical Treatment of Patients with Tumor-induced Osteomalacia Located in the Hip Bones: A Retrospective Analysis of 10 Years in a Single Center

OBJECTIVE

The orthopedic surgical treatment strategies for patients with tumor-induced osteomalacia (TIO) require improvement, especially for patients where the causative tumors are located in surgically challenging areas, requiring a greater degree of in-depth investigation. This work aims to summarize and investigate clinical features and orthopedic surgical treatment effects of patients with tumor-induced osteomalacia (TIO), whose causative tumors are located in the hip bones.

METHODS

A retrospective analysis was conducted on the clinical data of all patients diagnosed with culprit tumors located in the hip bones who underwent surgical treatment at the orthopedic bone and soft tissue tumor sub-professional group of Peking Union Medical College Hospital from January 2013 to January 2023. This retrospective study summarized the clinical data, preoperative laboratory test results, imaging findings, surgery-related data, perioperative changes in blood phosphorus levels, and postoperative follow-up data of all patients who met the inclusion criteria. Normally distributed data are presented as mean and standard deviation, while non-normally distributed data are shown as the means and 25th and 75th interquartile ranges.

RESULTS

The clinical diagnostic criteria for TIO were met by all 16 patients, as confirmed by pathology after surgery. Among the 16 patients, we obtained varying degrees of bone pain and limited mobility (16/16), often accompanied by difficulties in sitting up, walking, and fatigue. An estimated 62.5% (10/16) of patients had significantly shorter heights during the disease stages. All 16 patients underwent surgical treatment for tumors in the hip bones, totaling 21 surgeries. In the pathogenic tumor, there were 16 cases of skeletal involvement and none of pure soft tissue involvement. Out of the 16 patients, 13 cases had a gradual increase in blood phosphorus levels following the latest orthopedic surgery, which was followed up for 12 months to 10 years. Due to unresolved conditions after the original surgery, four patients received reoperation intervention. Two cases of refractory TIO did not improve in their disease course.

CONCLUSION

In summary, the location of the causative tumor in the hip bone is hidden and diverse, and there is no defined orthopedic surgical intervention method for this case in clinical practice. For patients with TIO where the tumors are located in the hip bones, surgical treatment is difficult and the risk of postoperative recurrence is high. Careful identification of the tumor edge using precise preoperative positioning and qualitative diagnosis is crucial to ensure adequate boundaries for surgical resection to reduce the likelihood of disease recurrence and improve prognosis.

Tumor-induced osteomalacia

Tumor-induced osteomalacia is one of paraneoplastic syndromes characterized by hypophosphatemia caused by excessive actions of fibroblast growth factor 23 (FGF23). Since the cloning of FGF23 about 20 years ago, more widespread awareness of this disease has been achieved. However, there still remain several difficulties in the management of patients with this disease. In this review, these clinical problems are discussed together with the physiological and pathophysiological functions of FGF23. Personal proposals in the management of patients with suspected patients with tumor-induced osteomalacia are also presented.

Emerging Role of Gallium-68 DOTANOC PET/CT Guided Radiofrequency Ablation in the Treatment of Tumor-induced Osteomalacia

Tumor-induced osteomalacia (TIO) is a rare acquired form of hypophosphatemia that can be cured when the tumor responsible is completely removed. These tumors can be small and located in anatomically challenging areas, rendering surgery both risky and extensive. Radiofrequency ablation (RFA) has been explored as an effective treatment option for such tumors. We present a case of a 35-year-old man exhibiting clinical and biochemical features consistent with TIO. The culprit lesion was not detectable on the whole-body computed tomography (CT) scan. Gallium (Ga-68) DOTANOC positron emission tomography (PET)/CT showed increased uptake in the left acetabulum and magnetic resonance imaging (MRI) confirmed the location of the tumor. Given the risky anatomical location, we opted for less-invasive RFA. Following an unsuccessful attempt at CT-guided RFA of the lesion, we used real-time Ga-68 DOTANOC PET/CT guidance for precise imaging during the ablation procedure. Our patient achieved complete remission both clinically and biochemically after RFA. This response was also evident by the absence of tracer uptake in follow-up imaging. In conclusion, DOTANOC PET/CT-guided RFA can serve as a safe and effective treatment for patients with tumors causing TIO. This modality proves valuable when surgical resection is not a viable option.

Extended curettage for tumour-induced osteomalacia in the bone

BACKGROUND

extended curettage is generally used to treat infiltrative bone tumours. However, the extent of the curettage performed in previous studies remains unclear. This study aimed to investigate the efficacy of extended curettage for bone tumour-induced osteomalacia.

METHODS

we included 12 patients with tumour-induced osteomalacia who underwent extended curettage at our hospital between 2000 and 2022. Extended curettage was applied in cases where tumour resection could cause functional impairment or necessitate complex reconstruction. We investigated patients' clinical and oncological outcomes.

RESULTS

patients had a mean age of 55 (24-81) years, and the median follow-up duration after surgery was 3.9 (1.0-14.0) years. The causative tumours were located in the pelvis and lumbar spine. Imaging revealed the tumours to be of the sclerotic, intertrabecular, lytic and mixed types. Intraoperative 3D fluoroscopy was used in 10 patients. Extended curettage with high-speed burring and adjuvant therapy with cauterization using an electric scalpel and ethanol resulted in a remission rate of 83%; no recurrence or metastasis was observed in cases of early postoperative biochemical remission. In cases where the causative tumour was at the lumbar spine and ischium close to the acetabulum, no postoperative biochemical remission was observed, and conservative treatment was continued. Except for one patient with a tumour in the lumbar spine, all patients could walk without a cane.

CONCLUSIONS

extended curettage for bone tumour-induced osteomalacia is oncologically and functionally favourable, especially in cases where resection of the causative tumour could cause functional impairment or necessitate complex reconstruction.

Preoperative evaluation and orthopedic surgical strategies for tumor-induced osteomalacia

Tumor-induced osteomalacia (TIO), also known as oncogenic osteomalacia, is very rare, with about 1000 reported cases globally. Removing most TIO culprit tumors requires the evaluation and intervention of orthopedic doctors. However, orthopedic doctors often have a poor understanding of the optical treatment of TIO due to its rarity. In addition, most TIO patients lack specific clinical manifestations. Also, the clinical localization and qualitative diagnosis of TIO are difficult and thus can easily be misdiagnosed and mistreated. Furthermore, the true incidence rate of TIO may be underestimated. Although many breakthroughs have been made in exploring the pathogenesis, clinical diagnosis, and treatment of TIO, rational and standardized orthopedic surgical treatment experience summary and sorting for TIO patients are lacking. In this article, the recent experience and progress in the field of orthopedic surgical treatment for TIO globally have been summarized, providing a theoretical basis and new clinical practice guidance for the rational treatment of TIO patients.

Locoregional Thermal and Chemical Tumor Ablation: Review of Clinical Applications and Potential Opportunities for Use in Low- and Middle-Income Countries

This review highlights opportunities to develop accessible ablative therapies to reduce the cancer burden in LMICs.

Imaging characteristics of phosphaturic mesenchymal tumors

BACKGROUND

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome associated with phosphaturic mesenchymal tumors (PMTs). Localization of the causative tumor in these cases is an arduous task since the culprit lesions are usually small, slow-growing, and can be located almost anywhere from head to toe.

PURPOSE

To describe the morphological characteristics of histologically proven PMTs on various radiological modalities.

MATERIAL AND METHODS

After institutional ethical approval, this retrospective study analyzed 20 cases with a histopathological evidence of PMT. Various imaging characteristics of the tumors on available computed tomography (CT) and magnetic resonance imaging (MRI) scans were evaluated. Descriptive statistical analyses were conducted.

RESULTS

The tumors were located in diverse locations: lower extremities (n = 10); head and neck (n = 5); vertebral column (n = 3); pelvis (n = 1); and upper extremities (n = 1). Bone lesions seen on CT had variable morphology: sclerotic (n = 3/8, 37.5%); lytic (n = 3/8, 37.5%), and both lytic and sclerotic (n = 2/8, 25%) with presence of narrow zone of transition in all cases (n = 8/8) and amorphous internal matrix calcifications in 25% of cases (n = 2/8). Of the tumors, 68.4% (n = 13/19) were hypointense on T1 and all of them showed hyperintense signal on T2-weighted and STIR images (n = 19/19) and contrast enhancement (n = 16/16). Of the tumors, 66.7% (n = 6/9) showed restricted diffusion. DOTANOC PET/CT showed tumor uptake in all cases (n = 8/8).

CONCLUSION

PMTs may have variable and non-specific tumor appearances on various imaging modalities. However, in an appropriate clinical scenario and a background of suggestive biochemical work-up, the radiologist should keep a high index of suspicion.

Global guidance for the recognition, diagnosis, and management of tumor-induced osteomalacia

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by mesenchymal tumors that secrete fibroblast growth factor 23 (FGF23). Patients present with progressive bone pain, muscle weakness, and fragility fractures. TIO is characterized by hypophosphatemia, excess renal phosphate excretion, and low/inappropriately normal 1,25-dihydroxyvitamin D (1,25(OH)₂ D) levels. Rarity and enigmatic clinical presentation of TIO contribute to limited awareness among the medical community. Accordingly, appropriate diagnostic tests may not be requested, leading to delayed diagnosis and poorer patient outcomes. We have developed a global guidance document to improve the knowledge of TIO in the medical community, enabling the recognition of patients with TIO and appropriate referral. We provide recommendations aiding diagnosis, referral, and treatment, helping promote a global standard of patient management. We reviewed the literature and conducted a three-round Delphi survey of TIO experts. Statements were drafted based on published evidence and expert opinions (≥70% consensus required for final recommendations). Serum phosphate should be measured in patients presenting with chronic muscle pain or weakness, fragility fractures, or bone pain. Physical examination should establish features of myopathy and identify masses that could be causative tumors. Priority laboratory evaluations should include urine/serum phosphate and creatinine to assess renal tubular reabsorption of phosphate and TmP/GFR, alkaline phosphatase, parathyroid hormone, 25-hydroxyvitamin D, 1,25(OH)₂ D, and FGF23. Patients with the clinical/biochemical suspicion of TIO should be referred to a specialist for diagnosis confirmation, and functional imaging should be used to localize causative tumor(s). Recommended treatment is tumor resection or, with unresectable/unidentifiable tumors, phosphate salts plus active vitamin D, or burosumab.

Novel Therapeutic Agents for Rare Diseases of Calcium and Phosphate Metabolism

The last decade has been revolutionary regarding the management of rare bone diseases caused by impaired calcium and phosphate metabolism. Elucidation of the underlying genetic basis and pathophysiologic alterations has been the determinant factor for the development of new, disease-specific treatment agents. The phosphaturic hormone Fibroblast Growth Factor 23 (FGF23) possesses a critical role in the pathogenesis of various hypophosphatemic disorders. Among them, the genetic disorder of X-linked hypophosphatemia and the acquired syndrome of tumor-induced osteomalacia, although very rare, have attracted the scientific community's attention towards designing an FGF23-inhibitor as a potential specific therapy. The monoclonal antibody burosumab was approved for the treatment of children and adult patients with X-linked hypophosphatemia and recently for tumor-induced osteomalacia patients, demonstrating benefits regarding their symptoms, biochemical profile and bone mineralization status. Asfotase alfa is a hydroxyapatite-targeted recombinant alkaline phosphatase, an enzymatic replacement therapy, substituting the defective activity of tissue non-specific alkaline phosphatase, in patients suffering from hypophosphatasia. Promising data regarding its favorable effect on survival rate, bone quality, fracture healing, muscle strength, mobility, respiratory function, and general quality of life have led to the approval of the drug for the treatment of childhood-onset hypophosphatasia. Given the high costs of treatment for both agents and their limited clinical use until now, more data are needed to define patients' characteristics that make them ideal candidates for therapy. Long-term safety issues also need to be clarified.

[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.

Infigratinib Reduces FGF23 and Increases Blood Phosphate in Tumor‐Induced Osteomalacia

Tumor‐induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by ectopic production of fibroblast growth factor 23 (FGF23) by phosphaturic mesenchymal tumors (PMTs). Acting on renal tubule cells, excess FGF23 decreases phosphate reabsorption and 1,25‐dihydroxy‐vitamin D (1,25D) production, leading to hypophosphatemia, impaired bone mineralization, pain, and fractures. Fibronectin 1‐fibroblast growth factor receptor 1 (FN1‐FGFR1) gene fusions have been identified as possible drivers in up to 40% of resected PMTs. Based on the presumptive role of FGFR1 signaling by chimeric FN1‐FGFR1 proteins, the effectiveness of infigratinib, a FGFR1‐3 tyrosine kinase inhibitor, was studied in an open‐label, single‐center, phase 2 trial. The primary endpoint was persistent normalization of blood phosphate and FGF23 after discontinuation. Four adults with TIO (two nonlocalized, two nonresectable PMTs) were treated with daily infigratinib for up to 24 weeks. All patients had a favorable biochemical response that included reduction in intact FGF23, and normalization of blood phosphate and 1,25D. However, these effects disappeared after drug discontinuation with biochemistries returning to baseline; no patients entered biochemical remission. In the two patients with identifiable tumors, 68Gallium (68Ga)‐DOTATATE and 18Fluoride (18F)‐Fluorodeoxyglucose (FDG) PET/CT scans showed a decrease in PMT activity without change in tumor size. Patients experienced mild to moderate, treatment‐related, dose‐limiting adverse events (AEs), but no serious AEs. Three patients had dose interruptions due to AEs; one patient continued on a low dose for the entire 24 weeks and one patient stopped therapy at 17 weeks due to an AE. The study closed early due to a failure to meet the primary endpoint and a higher‐than‐expected incidence of ocular AEs. Infigratinib treatment lowered FGF23, increased blood phosphate, and suppressed PMT activity, confirming the role of FGFR signaling in PMT pathogenesis. However, treatment‐related AEs at efficacy doses and disease persistence on discontinuation support restricting the use of infigratinib to patients with life‐limiting metastatic PMTs. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

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.

Diagnosis and Management of Tumor-induced Osteomalacia: Perspectives From Clinical Experience

Purpose

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome of abnormal phosphate and vitamin D metabolism caused by typically small endocrine tumors that secrete fibroblast growth factor 23 (FGF23). TIO is characterized clinically by progressive musculoskeletal pain, fatigue, proximal muscle weakness, and multiple fractures, leading to long-term disability. Misdiagnosis and delayed diagnosis are common because of the nonspecific symptoms, and several years may elapse before patients receive an accurate diagnosis and appropriate treatment. Thus, it is vital that awareness of the appropriate recognition and management of TIO is increased among healthcare professionals who may encounter patients with suspected TIO.

Methods

A roundtable meeting was held on 10 January 2020 in Dallas, TX, USA, to gather perspectives on the diagnosis and treatment of TIO. The following topics were considered: clinical presentation, patient history, differential diagnosis, laboratory assessment, imaging, venous sampling, and treatment.

Results

This report provides a summary of our collective experiences in the management of TIO.

Main conclusions

Laboratory tests are mandatory to expedite TIO diagnosis and should include measurement of fasting serum phosphorus, renal phosphate reabsorption, serum 1,25-dihydroxyvitamin D, and serum FGF23 levels. Functional and anatomical imaging are essential to locate the FGF23-secreting tumor(s) causing TIO. Surgical resection is often a curative treatment when the tumor can be localized; however, better management of patients who cannot be operated on with targeted therapies is needed. Further efforts to increase awareness of TIO within the medical community, and education on recommended diagnostic and treatment pathways are required to improve the management of this debilitating disease.

Persistent phosphaturic mesenchymal tumor causing tumor-induced osteomalacia treated with image-guided ablation

Phosphaturic mesenchymal tumors (PMTs) can present with vague symptoms of diffuse bone pain with pathologic fractures that often lead to a delayed diagnosis. We present a 60-year-old patient with a PMT that was persistently hypophosphatemic after resection, who was then successfully treated with cryoablation of the tumor. Tumor-induced osteomalacia (TIO) is a rare cause of hypophosphatemia characterized by vague symptoms of gradual muscle weakness and diffuse bone pain with pathologic fractures that often lead to a delayed diagnosis. This condition is usually caused by benign phosphaturic mesenchymal tumors (PMTs). Here, we present a case of persistent PMT after surgical resection treated with image-guided ablation. We present the patient's clinical examinations and laboratory findings (phosphorus, 1,25 (OH)₂D, FGF-23, Intact PTH). Representative histologic images of a PMT are also presented. A 61-year-old male was evaluated for persistent hypophosphatemia and presumed osteomalacia. Six years earlier, he underwent surgical excision of a left ischial mass after presenting with TIO. The pathology was consistent with a PMT; however, hypophosphatemia persisted suggesting incomplete resection. He was treated with calcitriol and phosphate salts. A PET Ga68 dotatate scan of the patient revealed an avid left ischial mixed lytic and sclerotic lesions with marked amount of radiotracer uptake, suggesting persistent tumor. The patient was resistant to re-excision of the tumor due to the extended recovery period from his prior surgery and was treated instead with cryoablation of the tumor. His biochemical findings of hypophosphatemia and elevated FGF23 resolved after the ablation and have remained normal for 5 months after surgery. In patients with TIO, wide surgical excision is the treatment of choice. When this is not possible, image-guided ablation is an alternative therapeutic option.

Surgical margin for phosphaturic mesenchymal tumors in soft tissues: An analysis of the radiological histopathological correlation

BACKGROUND

Phosphaturic mesenchymal tumors primarily cause tumor-induced osteomalacia, a rare paraneoplastic syndrome, and half occur in soft tissues. There are few reports about the surgical margins of these tumors. This study aimed to clarify the optimal surgical margin for phosphaturic mesenchymal tumors by analyzing radiological and histopathological features.

METHODS

This study included eight cases, seven primary and one recurrent, of tumor-induced osteomalacia caused by soft-tissue phosphaturic mesenchymal tumors that were surgically treated between January 2000 and January 2019. We evaluated the radiological and histopathological features of all tumors and investigated the correlation of these features, the surgical margin, and recurrence of hypophosphatemia.

RESULTS

The tumors were located in superficial (n = 5) and deep (n = 3) tissues. Six of the eight tumors had a clear boundary, but five had an irregular margin. Three tumors had a hypointense rim on T2-weighted images, indicating fibrous tumor encapsulation. Histopathological analysis revealed infiltrative growth in six of the eight tumors, which correlated with an irregular margin seen on imaging. Although there was no recurrence in patients treated with an intended wide margin >1 cm, one of the three patients treated with marginal tumor resection experienced a recurrence of hypophosphatemia, with histopathological analysis showing infiltration of subcutaneous fat. In contrast, two tumors with clear boundaries, regular margins, and fibrous capsule seen on imaging, had no infiltrative growth and were cured by marginal resection. In one recurrent case, tumor infiltration was observed in the previous surgical scar, which was not detected on preoperative imaging.

CONCLUSIONS

Soft-tissue phosphaturic mesenchymal tumors with an irregular boundary seen on imaging tend to be infiltrative, especially into subcutaneous fat, and should be treated by at least a 1-cm wide margin resection. Tumors with a fibrous capsule with clear and regular margins are cured by marginal margin resection. These findings could inform surgeons' decisions regarding the resection of soft-tissue phosphaturic mesenchymal tumors.

Epidemiology of Tumor-Induced Osteomalacia in Denmark

Tumor-induced osteomalacia (TIO) is a rare, acquired condition of phosphate wasting due to phosphaturic mesenchymal tumors. Because the incidence and prevalence of TIO is unknown, we conducted an observational cohort study using national Danish health registers for the period 2008 to 2018 to obtain such information. The study also aimed to describe the demographics of the TIO population and the prognosis. The operational definition was based on hypophosphatemia or adult osteomalacia diagnoses, combined with prescriptions used in the initial management and procedures consistent with advanced imaging used for locating tumors. The incidence of TIO in Denmark was found to be below 0.13 per 100,000 person years for the total population of the country and 0.10 per 100,000 in adult-onset disease. The prevalence of TIO was estimated to be no more than 0.70 per 100,000 persons for the total population and 0.43 per 100,000 in adults. In 2018, there were a maximum of nine new cases of TIO in Danish adults. Mortality was low but few patients fulfilled the protocol cure criterion during the observation period. TIO has no ICD-10 code and limitations to the study include lack of information on serum biochemistry and on the use of phosphate supplements. Strengths include the use of long-term longitudinal, national hospital and prescription data from a country with universal healthcare. Given the very small patient population with TIO and the known delay to diagnosis and cure, management of patients with suspected TIO should be centralized.

Application of ultrasound-guided biopsy and percutaneous radiofrequency ablation in 2 cases with phosphaturic mesenchymal tumor and literature review

Tumor-induced osteomalacia (TIO) is a vanishingly rare paraneoplastic syndrome which is usually caused by phosphaturic mesenchymal tumors (PMTs). The conventional treatment for PMTs is total resection, and ultrasound-guided radiofrequency ablation (RFA) can also be used for the treatment of PMTs patients, especially for patients in whom complete resection may lead to serious complications. We report two cases with PMT who presented syndrome with progressive musculoskeletal complaints and performed ultrasound-guided biopsy and RFA. Ultrasound-guided RFA, which is a safe and effective minimally invasive treatment option, appears to be a valuable alternative to surgery for patients presenting with PMT. We are the first reported case of RFA guided by ultrasonography in the treatment of PMT.

Tumor-Induced Osteomalacia

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by tumoral production of fibroblast growth factor 23 (FGF23). The hallmark biochemical features include hypophosphatemia due to renal phosphate wasting, inappropriately normal or frankly low 1,25-dihydroxy-vitamin D, and inappropriately normal or elevated FGF23. TIO is caused by typically small, slow growing, benign phosphaturic mesenchymal tumors (PMTs) that are located almost anywhere in the body from the skull to the feet, in soft tissue or bone. The recent identification of fusion genes in a significant subset of PMTs has provided important insights into PMT tumorigenesis. Although management of this disease may seem straightforward, considering that complete resection of the tumor leads to its cure, locating these often-tiny tumors is frequently a challenge. For this purpose, a stepwise, systematic approach is required. It starts with thorough medical history and physical examination, followed by functional imaging, and confirmation of identified lesions by anatomical imaging. If the tumor resection is not possible, medical therapy with phosphate and active vitamin D is indicated. Novel therapeutic approaches include image-guided tumor ablation and medical treatment with the anti-FGF23 antibody burosumab or the pan-FGFR tyrosine kinase inhibitor, BGJ398/infigratinib. Great progress has been made in the diagnosis and treatment of TIO, and more is likely to come, turning this challenging, debilitating disease into a gratifying cure for patients and their providers.

FGF23 and Bone and Mineral Metabolism

FGF23 is a phosphotropic hormone produced by the bone. FGF23 works by binding to the FGF receptor-Klotho complex. Klotho is expressed in several limited tissues including the kidney and parathyroid glands. This tissue-restricted expression of Klotho is believed to determine the target organs of FGF23. FGF23 reduces serum phosphate by suppressing the expression of type 2a and 2c sodium-phosphate cotransporters in renal proximal tubules. FGF23 also decreases 1,25-dihydroxyvitamin D levels by regulating the expression of vitamin D-metabolizing enzymes, which results in reduced intestinal phosphate absorption. Excessive actions of FGF23 cause several types of hypophosphatemic rickets/osteomalacia characterized by impaired mineralization of bone matrix. In contrast, deficient actions of FGF23 result in hyperphosphatemic tumoral calcinosis with high 1,25-dihydroxyvitamin D levels. These results indicate that FGF23 is a physiological regulator of phosphate and vitamin D metabolism and indispensable for the maintenance of serum phosphate levels.

Clinical Characteristics and Surgical Outcomes of Sinonasal Lesions Associated With Tumor-Induced Osteomalacia

OBJECTIVE

To investigate the clinical characteristics and surgical outcomes of sinonasal tumors associated with tumor-induced osteomalacia (TIO).

STUDY DESIGN

Retrospective case series.

SETTING

Single tertiary center.

METHODS

We studied the clinical characteristics and surgical outcomes of 43 patients (22 male, 21 female) who had lesions in the nasal cavity and paranasal sinus associated with TIO and underwent surgery between August 2006 and November 2019.

RESULTS

The mean ± SD duration between the onset of symptoms and surgery was 3.9 ± 2.6 years. The most common tumor site was the ethmoid sinus (76.7%), and the skull base was involved in 12 cases. Phosphaturic mesenchymal tumors were diagnosed in 41 patients, among whom there was 1 multifocal case. Another 2 cases involved odontogenic fibroma and hemangiofibroma, respectively. Serum phosphorus normalized in 39 cases within 4.4 ± 2.3 days, and serum fibroblastic growth factor 23 normalized within 1 day; clinical symptoms, however, gradually improved within several months after the first operation. There was no significant difference in the recovery rate between endoscopic and open surgery (P = 0.639). Two patients with recurrent cases and 2 with nonremission cases recovered after a sinonasal reoperation. The patient with a multifocal case recovered after the resection of the tumors in the ethmoid sinus and mandible. The overall recovery rate was 97.7%.

CONCLUSION

Most sinonasal tumors associated with TIO are located in the ethmoid sinus, and the skull base is involved in some cases. Complete excision of the tumor leads to recovery, and endoscopic surgery could achieve recovery rates similar to those of open surgery.

Peptide Receptor Radionuclide Therapy for a Phosphaturic Mesenchymal Tumor

Tumor-induced osteomalacia is a very rare paraneoplastic syndrome. It can be caused by phosphaturic mesenchymal tumor (PMT), a generally benign tumor that produces fibroblast growth factor 23 (FGF-23), which can cause a severe renal phosphate wasting syndrome. Upon complete surgical removal of the tumor, FGF-23 normalizes and the osteomalacia is cured. In cases in which surgery is not feasible, radiofrequency ablation (RFA) is the treatment of choice. We describe a case with a PMT situated in the sacrum, in close proximity to the sacral plexus. Both surgery and RFA were considered potentially nerve damaging. Since the tumor showed expression of somatostatin receptors, we opted for a peptide receptor radionuclide therapy (PRRT) with ¹⁷⁷Lu-DOTATOC. However, the therapy did not show the expected success, since the FGF-23 level had even temporarily increased. The patient was then successfully treated with RFA. A partial remission of the tumor was achieved and FGF-23 levels nearly normalized. Despite some severe neurological side effects, the patient showed a remarkable clinical improvement, with no symptoms of osteomalacia within a few weeks.

Multidisciplinary patient care in X-linked hypophosphatemic rickets: one challenge, many perspectives

X‑linked hypophosphatemic rickets (XLH, OMIM #307800) is a rare genetic metabolic disorder caused by dysregulation of fibroblast-like growth factor 23 (FGF23) leading to profound reduction in renal phosphate reabsorption. Impaired growth, severe rickets and complex skeletal deformities are direct consequences of hypophosphatemia representing major symptoms of XLH during childhood. In adults, secondary complications including early development of osteoarthritis substantially impair quality of life and cause significant clinical burden. With the global approval of the monoclonal FGF23 antibody burosumab, a targeted treatment with promising results in phase III studies is available for children with XLH. Nevertheless, complete phenotypic rescue is rarely achieved and remaining multisystemic symptoms demand multidisciplinary specialist care. Coordination of patient management within the major medical disciplines is a mainstay to optimize treatment and reduce disease burden. This review aims to depict different perspectives in XLH patient care in the setting of a multidisciplinary centre of expertise for rare bone diseases.