Radiofrequency ablation, an effective modality of treatment in tumor-induced osteomalacia: a case series of three patients

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.

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.

Tumor-induced osteomalacia: An overview

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

Thermal Ablation for Treating Tumor-induced Osteomalacia in a Patient With IV Phosphate Dependency

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome associated with tumors secreting fibroblast growth factor 23 that can be cured with complete surgical resection of the tumor. However, when these tumors are at difficult locations, less invasive modalities such as thermal ablation (TA) might be a good alternative. A 40-year-old woman was seen for a second opinion because of severe hypophosphatemia with complaints of fatigue, myalgia, and muscle weakness for which she needed IV phosphate for 15 to 18 hours per day in addition to oral alfacalcidol and phosphate. Initial laboratory results revealed hypophosphatemia (0.59 mmol/L [1.83 mg/dL]; reference range, 0.90-1.50 mmol/L [8.40-10.2 mg/dL]), increased fibroblast growth factor 23 levels (137 RU/mL; reference range, <125 RU/mL), and a reduced TmP-GFR (0.47 mmol/L; reference range, 0.8-1.4 mmol/L). Gallium-positron emission tomography/computed tomography (CT) showed moderately increased uptake at thoracic vertebra (Th) 8 and mildly increased uptake at Th7, suggestive of TIO. Complete tumor removal would have required resection of at least 1 vertebral body. Therefore, CT-guided TA was performed at Th8. No complications were observed, and in the months after, treatment with IV phosphate could be discontinued, indicating a satisfying result from the procedure. This extreme TIO case demonstrates that CT-guided TA can be an alternative to extensive or risky classical surgery.

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.

Tumor-induced Osteomalacia: A Systematic Review and Individual Patient's Data Analysis

CONTEXT

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome, usually caused by small, benign, and slow-growing phosphaturic mesenchymal tumors. Clinically, TIO is characterized by renal phosphate leak, causing hypophosphatemia and osteomalacia. This review was performed to assess the clinical characteristics of TIO patients described worldwide so far.

EVIDENCE ACQUISITION

On June 26, 2021, a systematic search was performed in Medline, Google Scholar, Google book, and Cochrane Library using the terms: "tumor induced osteomalacia," "oncogenic osteomalacia," "hypophosphatemia." There were no language restrictions. This review was performed according to Preferred Reporting Items for Systematic reviews and Meta-Analyses criteria.

EVIDENCE RESULTS

Overall, 1725 TIO cases were collected. TIO was more frequent in adult men, who showed a higher incidence of fractures compared with TIO women. The TIO-causing neoplasms were identified in 1493 patients. The somatostatin receptor-based imaging modalities have the highest sensitivity for the identification of TIO-causing neoplasms. TIO-causing neoplasms were equally located in bone and soft tissues; the latter showed a higher prevalence of fractures and deformities. The surgery is the preferred TIO definitive treatment (successful in > 90% of patients). Promising nonsurgical therapies are treatments with burosumab in TIO patients with elevated fibroblast growth factor-23 levels, and with radiolabeled somatostatin analogs in patients with TIO-causing neoplasm identified by somatostatin receptor-based imaging techniques.

CONCLUSION

TIO occurs preferentially in adult men. The TIO clinical expressiveness is more severe in men as well as in patients with TIO-causing neoplasms located in soft tissues. Treatments with burosumab and with radiolabeled somatostatin analogs are the most promising nonsurgical therapies.

Tumor induced osteomalacia: A single center experience on 17 patients

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome due to a phosphaturic tumor, which overproduces Fibroblast Growth Factor 23 (FGF-23), causing hyperphosphaturia, hypophosphatemia, low 1,25(OH)₂D and osteomalacia. Tumor localization is critical, diagnostic delay ranges from 2.5 to 28 years and to date surgical removal is considered effective treatment. We retrospectively evaluated patients with definite diagnosis of TIO referred to a tertiary Rheumatology Center between September 2000 and May 2020, investigating clinical management and disease outcome. We included 17 patients: 10 (58.8%) were females, mean age at diagnosis was 55.3 ± 13.9 years (mean ± standard deviation), with a diagnostic delay from symptoms onset to tumor detection of 6.6 ± 6.25 years. Biochemical data were: serum phosphorus 1.3 ± 0.4 mg/dL (Reference Range: 2.5-4.6), serum 1,25(OH)₂D 31.8 ± 22.9 ng/mL (RR: 25-86), intact FGF-23, 358.9 ± 677 pg/mL (RR: 25-45); 24 h-Urine Phosphorus was increased in only 2 patients, while tubular reabsorption of phosphate (TRP) was decreased in all patients confirming a renal phosphate wasting. In 2013 ⁶⁸Ga- DOTA-based PET/CT was introduced in routinely practice and diagnostic delay was consistently reduced (from 8.6 ± 7.9 to 4.3 ± 2.4 years). Thirteen patients underwent surgery, one patient underwent radiofrequency ablation; 3 patients, not eligible for surgery, were treated only with supplements of phosphorus and calcitriol. One was started on Burosumab after several unsuccessful surgical attempts. After surgery or ablation, 8 patients had complete remission, 3 TIO persistence, and 3 had overtime relapse. Relapses were observed only in patients who previously underwent closed biopsy. To our knowledge, this is the widest European cohort of TIO patients in the last two decades. We confirm a usual diagnostic delay and recommend a stepwise diagnostic approach. Tumor biopsy is not recommended due to the potential cell spilling. Surgery is generally considered a definitive treatment, even though other approaches have been successful in curing TIO. Active surveillance on possible recurrence is always needed. Burosumab appears a promising therapy.

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.

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.

Diagnostic efficiency of 68Ga-DOTANOC PET/CT in patients with suspected tumour-induced osteomalacia

OBJECTIVES

Currently, the main challenge in tumour-induced osteomalacia (TIO) is the difficulty in locating culprit tumours for definitive diagnosis and surgical therapy. Herein, we retrospectively evaluate the efficiency of ⁶⁸Ga-DOTANOC PET/CT in the localisation and diagnosis of TIO, and compared with ¹⁸F-FDG.

METHODS

Twenty-four consecutive patients with hypophosphataemic osteomalacia (HO) and suspicion of TIO who were referred to our centre for ⁶⁸Ga-DOTANOC PET/CT scanning were retrospectively reviewed. The images were evaluated qualitatively as well as semi-quantitatively, and imaging results were compared with the final diagnoses.

RESULTS

Among the total of 21 patients who were included in the final analyses, 17 were diagnosed with TIO, while four were proven to have other causes of HO. ⁶⁸Ga-DOTANOC PET/CT produced positive results in 16 of the 17 patients with TIO, representing a sensitivity of 94.1%. Moreover, the ⁶⁸Ga-DOTANOC PET/CT results were negative in 3 of the 4 patients without TIO, representing a specificity of 75.0%. The overall accuracy of ⁶⁸Ga-DOTANOC PET/CT in locating the tumours responsible for TIO is 90.5%. In particular, ⁶⁸Ga-DOTANOC PET/CT detected the culprit tumours in 4 out of 10 patients with negative results on previous ¹⁸F-FDG PET/CT and showed a significantly higher T/M ratio of tumours than ¹⁸F-FDG PET/CT in the same patients (n = 10; 4.76 ± 3.08 vs 1.95 ± 1.33, p < 0.05).

CONCLUSIONS

⁶⁸Ga-DOTANOC PET/CT is an accurate imaging modality in the localisation of tumours for TIO. It is superior to ¹⁸F-FDG PET/CT and may be useful in the differential diagnosis of HO.

KEY POINTS

• TIO should be considered a possible cause for patients diagnosed with HO, which usually needs to be differentiated from other aetiologies. • ⁶⁸Ga-DOTANOC PET/CT is an accurate imaging modality in locating culprit tumours for TIO, superior to ¹⁸F-FDG PET/CT.

Phosphaturic Mesenchymal Tumor of Soft Tissue of the Foot: Report of a Case With Review of the Literature

Phosphaturic mesenchymal tumor (PMT) is a rare neoplasm that ectopically secretes fibroblast growth factor 23, a bone cell-derived protein that regulates phosphate homeostasis. The overproduction of fibroblast growth factor 23 causes a paraneoplastic syndrome characterized by hyperphosphaturia, hypophosphatemia, hypovitaminosis D, and vitamin D refractory rickets/osteomalacia, effects that disappear with tumor removal. The PMT may occur in several anatomic regions, mainly in the limbs, usually involving both soft tissue and bone. Acral locations occur in 10% to 15% of the cases, mostly in the feet, with 95 cases reported in this anatomic region to date. We report a case of a PMT in a young adult male who presented in 2007 with the classic constellation of signs and symptoms. A small soft-tissue tumor was detected in his right heel, 3 years after exhaustively seeking for it by various imaging techniques performed at different institutions. Before the tumor was detected, attempts to manage this patient's osteomalacia with phosphate and vitamin D (both calcitriol and ergocalciferol) supplementation were unsuccessful. Following surgical resection, the patient experienced prompt correction of the phosphaturia and gradual reconstitution of his bone mineralization. The pathologic diagnosis was (benign) PMT, mixed connective tissue type. In 2019, 12 years after resection, the patient is asymptomatic, and his bone mineral homeostasis has been restored.

Tumor-induced osteomalacia: experience from three tertiary care centers in India

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by recalcitrant hypophosphatemia. Reports from the Indian subcontinent are scarce, with most being single center experiences involving few patients. Herein, we conducted a retrospective analysis of 30 patients of TIO diagnosed at three tertiary care hospitals in India. Patients with persistent hypophosphatemia (despite correction of hypovitaminosis D), normocalcemia, elevated alkaline phosphatase, low TmP/GFR and elevated or 'inappropriately normal' FGF23 levels were labeled as having TIO. They were sequentially subjected to functional followed by anatomical imaging. Patients with a well-localized tumor underwent excision; others were put on phosphorous and calcitriol supplementation. The mean age at presentation was 39.6 years with female:male ratio of 3:2. Bone pain (83.3%) and proximal myopathy (70%) were the chief complaints; 40% of cases had fractures. The mean delay in diagnosis was 3.8 years. Tumors were clinically detectable in four patients (13.3%). The mean serum phosphate was 0.50 mmol/L with a median serum FGF23 level of 518 RU/mL. Somatostatin receptor-based scintigraphy was found to be superior to FDG-PET in tumor localization. Lower extremities were the most common site of the tumor (72%). Tumor size was positively correlated with serum FGF23 levels. Twenty-two patients underwent tumor resection and 16 of them had phosphaturic mesenchymal tumors. Surgical excision led to cure in 72.7% of patients whereas disease persistence and disease recurrence were seen in 18.2% and 9.1% of cases, respectively. At the last follow-up, serum phosphate in the surgically treated group was significantly higher than in the medically managed group.

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

Tumor-induced osteomalacia (TIO) is a curable condition when the tumor is correctly located and completely removed. These tumors are, however, small and located in regions that make surgical removal difficult and sometimes risky in some patients. Experience of radiofrequency ablation (RFA) in the management of TIO is limited. We describe 3 patients with TIO who were treated in our hospital with RFA. They had suspected lesions in surgically difficult locations and were subjected to single sessions of RFA. The response was documented in terms of improvement in symptoms, normalization of hypophosphatemia and hyperphosphaturia, and disappearance of uptake on follow-up Ga⁶⁸ DOTANOC PET/CT imaging. All 3 patients had a clinical and biochemical profile consistent with TIO. The first patient (patient 1) had an intensely Ga⁶⁸ DOTANOC avid lesion involving the roof of right acetabulum. The second patient (patient 2) had a Ga⁶⁸ DOTANOC avid intramuscular lesion in left pectineus muscle and the third patient (patient 3) had a Ga⁶⁸ DOTANOC avid expansile osteolytic lesion involving the angle and ramus of right mandible. All 3 patients achieved complete biochemical as well as clinical remission with single sessions of RFA. Six months after the procedure, Ga⁶⁸ DOTANOC imaging revealed the absence of uptake at the previous sites, corroborating with the clinical improvement and normalization of hypophosphatemia and hyperphosphaturia. In conclusion, although surgical resection is the standard of care, RFA can be used successfully for treating patients with TIO. It can be an effective, less invasive, and safe modality of treatment in those patients where resection of the lesion is not possible because of inaccessible anatomical location or comorbidity that prohibits surgery. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

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.

Multimodality Image-Guided Cryoablation for Inoperable Tumor-Induced Osteomalacia

Tumor-induced osteomalacia (TIO) is a debilitating paraneoplastic condition caused by small phosphaturic mesenchymal tumors (PMTs) that secrete large amounts of the phosphate-regulating and vitamin D-regulating hormone, FGF23. Tumor removal results in cure. However, because of high perioperative comorbidity, either from tumor location or host factors, surgery is sometimes not an option. Tumor destruction via cryoablation may be an effective option for inoperable PMTs. Three subjects with a confirmed diagnosis of TIO were studied. All three underwent cryoablation of suspected PMTs rather than surgery due to significant medical comorbidities or challenging anatomical location. Subject 3 had tumor embolization 24 hours prior to cryoablation because of the size and hypervascularity of the tumor. The success of the tumor cryoablation was defined by normalization of serum phosphate and FGF23. Cryoablation resulted in a rapid decrease in plasma intact FGF23 by 24 hours postprocedure in all three subjects (0, 2, and 9 pg/mL, respectively) with normalization of blood phosphate by postprocedure day 3. Three-day renal tubular reabsorption of phosphate increased to 76%, 94%, and 95.2%, respectively; 1, 25(OH)₂ vitamin D increased to 84, 138, and 196 pg/ml, respectively. All three had dramatic clinical improvement in pain and weakness. Two subjects tolerated the procedure well with no complications; one had significant prolonged procedure-related localized pain. Although surgery remains the treatment of choice, cryoablation may be an effective, less invasive, and safe treatment for patients with difficult to remove tumors or who are poor surgical candidates. © 2017 American Society for Bone and Mineral Research.

Reports of 17 Chinese patients with tumor-induced osteomalacia

Tumor-induced osteomalacia (TIO) is a rare acquired form of hypophosphatemic osteomalacia, which is usually attributed to the overproduction of fibroblast growth factor 23 (FGF-23) by benign mesenchymal neoplasms. Localization and thereafter surgical resection of tumors lead to a cure. The present study aimed to investigate the clinical data, diagnostic methods, and follow-up after tumor resection at one medical center in Shanghai to characterize the profile of this rare disorder and to share our successful experience in diagnosis and treatment. Twenty-three patients with adult-onset hypophosphatemia osteomalacia seen in Shanghai Sixth People's Hospital from 2009 to 2014 and 95 normal individuals were enrolled. After taking a medical history and performing a physical examination, we analyzed the laboratory results (including the serum FGF-23 levels) and localized the tumors by ¹⁸F-fluorodeoxyglucose positron emission tomography and computed tomography (¹⁸F-FDG PET/CT), ^99mTc-octreotide (^99mTc-OCT) scintigraphy, and magnetic resonance imaging (MRI). On the basis of the results of laboratory tests and imaging findings, tumor resection was conducted in 17 patients with a certain diagnosis of TIO. The results demonstrated that the 17 patients (nine men and eight women, average age 46.6 ± 12.9 years) had TIO. FGF-23 level was elevated in 94.1 % of patients (16 of 17 patients) . Serum phosphorus level decreased in 100 % of patients. ¹⁸F-FDG PET/CT revealed five tumors, ^99mTc-OCT scintigraphy revealed two tumors, physical examination revealed nine tumors, and MRI revealed one tumor, among which 58.8 % of the causative tumors (10 of 17 tumors) were located in the lower extremities. After tumor resection, serum phosphorus levels normalized in 100 % of patients (all 17 patients) in 4-21 days and FGF-23 levels decreased in 90 % of patients (nine of ten patients). We found 64.7 % of the tumors (11 of 17 tumors) were phosphaturic mesenchymal tumors or a phosphaturic mesenchymal tumor mixed connective tissue variant. Measurement of serum phosphorus and FGF-23 levels in patients with suspected TIO is of paramount importance for diagnosing of TIO. ¹⁸F-FDG PET/CT, ^99mTc-OCT scintigraphy, and physical examination play a considerable role in revealing TIO-associated tumors. TIO-associated tumors were more frequently located in the lower extremities than in other places; thus, the lower extremities need to be carefully checked. Complete surgical resection results in normalization of parameters in laboratory tests and relief of symptoms of TIO patients.

Successful CT guided cryoablation of phosphaturic mesenchymal tumor in the soft tissues causing tumor-induced osteomalacia: a case report

We report the case of a 25-year-old male patient with tumor-induced osteomalacia from a 1.8-cm phosphaturic mesenchymal tumor in the right distal thigh, who was treated at our institution with a single session of CT-guided cryoablation in December 2015, which resulted in biochemical and clinical resolution. We present the clinical history, physical examination, biochemistry, functional imaging, anatomic characterization, and follow-up for clinical outcome. The response to treatment was documented in terms of normalization of serum fibroblastic growth factor 23 (FGF23) and phosphorous levels, symptomatic improvement, as well as normalization of bone mineralization on femur radiographs 3 months after the procedure. Although the first-line treatment for phosphaturic mesenchymal tumor-induced osteomalacia is wide surgical excision, CT-guided cryoablation widens the array of treatment options, especially in those patients who decline surgery or who are otherwise poor surgical candidates.

Tumor induced osteomalacia secondary to anaplastic thyroid carcinoma: A case report and review of the literature

Context

Tumor induced osteomalacia related to anaplastic thyroid cancer has never been reported.

Objective

We describe a case of tumor induced osteomalacia (TIO) in a patient with a fibroblast growth factor 23 (FGF-23) secreting anaplastic thyroid carcinoma. The current imaging modalities are reviewed.

Design and intervention

Clinical, biochemical, and radiological assessments were done, including computer tomography (CT) of the neck and skull to thigh positron emission tomography (PET)/CT. The patient underwent surgical tumor debulking three days after presentation due to airway compromise. Molecular studies of the resected tissue were performed using reverse transcriptase–polymerase chain reaction (RT-PCR) and gel electrophoresis for the phosphaturic mesenchymal tumor FGF-23.

Results

Resected tissue demonstrated features of anaplastic thyroid cancer with positive markers for FGF-23 protein, consistent with a FGF-23 secreting paraneoplastic tumor. The patient's metastatic burden rapidly progressed as demonstrated by a dramatic rise in serum FGF-23 levels and worsening hypophosphatemia in concert with progression of the metastatic lesions on PET/CT.

Conclusion

We believe that our patient's rapidly progressive anaplastic thyroid cancer was responsible for persistent hypophosphatemia and osteomalacia, substantiated by the finding of FGF-23 protein within the thyroid tumor cells. Our case indicates that anaplastic thyroid cancer can cause TIO.

Utility of Gallium-68 DOTANOC PET/CT in the localization of Tumour-induced osteomalacia

BACKGROUND

Tumour-induced osteomalacia (TIO) is a rare disorder characterized by hypophosphataemic osteomalacia caused by small mesenchymal tumours secreting fibroblast growth factor 23 (FGF 23). The most difficult part in the management of these patients is the localization of tumours causing TIO.

OBJECTIVE

We describe the utility of Gallium (Ga)-68 DOTANOC PET/CT in the localization of tumours causing TIO.

PATIENTS AND METHODS

The study was conducted in a single tertiary referral university teaching hospital in India. Ten patients with TIO who underwent Ga-68 DOTANOC PET/CT from the time period 2009 to 2014 were included in this study. Their detailed clinical history, biochemical parameters, imaging modalities, surgical interventions, histopathology and outcomes were reviewed.

RESULTS

Ga-68 DOTANOC PET/CT could correctly localize the tumours in TIO in 9 of the 10 cases in which it was performed. Complete resection of the tumour led to full clinical recovery in six of the ten patients; two patients who had partial resection and one patient who underwent radiofrequency ablation showed partial remission. One patient in whom Ga-68 DOTANOC PET/CT was positive in vertebral body with a low standardized uptake value (SUV) did not show up the tumour on surgery.

CONCLUSIONS

We conclude that Ga-68 DOTANOC PET/CT can be used as the first imaging modality in patients diagnosed with TIO. The extremely good outcome following the resection of these small otherwise undiagnosed tumours far outweighs its cost even in resource limited settings.