Phosphaturic Mesenchymal Tumors: Clinicopathologic, Immunohistochemical and Molecular Analysis of 22 Cases Expanding their Morphologic and Immunophenotypic Spectrum

Chronic hearing loss turns out being a calcified chondroid mesenchymal neoplasm with FN1::FGFR2 fusion

A 53 year old female presented with a six-year history of right-sided slow deterioration in hearing and a feeling of pressure in the right ear. The patient had not experienced any pain but reported some paresthesia of the right half of the tongue, whereas no further other cranial nerve deficits were evident. The otoscopy was unremarkable as well as the rest of the clinical ENT examination except for a slight asymptomatic swelling of the right cheek. Imaging findings showed an expansive tumor infiltrating and destroying the right lateral skull base. The tumor was partially composed of cystic/regressive lesions with high contrast media uptake. The tumor had high-signal intensity with water-sensitive sequences (T2w) and was hypointense on T1w images. We performed a tumor resection via a transparotideal-infratemporal approach. Histologically, the tumor was composed of granular variably calcified chondroid matrix with extensive regressive changes and granulation-like tissue reaction associated with calcinosis and crystal deposition. Molecular analysis of the tumor via the TruSight- RNA-Fusion panel detected a fusion involving FN1::FGFR2, consistent with "calcified chondroid mesenchymal neoplasm" (CCMN), a rare tumor entity recently defined by Liu et al 2021. In regular follow-up care no residual tumor has been detected in imaging studies (MRI and CT) within 2 years and 4 months. The biology and consequently the radio sensitivity cannot be defined precisely since long term results are missing due to the first description of this entity in 2021. As a consequence, surgical resection is recommended as the treatment of choice. Thorough clinical and radiological follow-up is mandatory as local recurrences are to be expected due to the infiltrative behavior. In case of a loco regional recurrence the fusion with FGFR2 may represent a therapeutic option for a targeted therapy on molecular level.

Treatment Advances in Tumor-Induced Osteomalacia

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by hypersecretion of fibroblast growth factor 23 (FGF23) by typically benign phosphaturic mesenchymal tumors (PMTs). FGF23 excess causes chronic hypophosphatemia through renal phosphate losses and decreased production of 1,25-dihydroxy-vitamin-D. TIO presents with symptoms of chronic hypophosphatemia including fatigue, bone pain, weakness, and fractures. Definitive treatment is surgical resection of the PMT with wide margins. Other therapeutic options are necessary when the tumor is unable to be localized, not amenable to complete resection, or when the patient is not a good surgical candidate. Alternative ablative approaches such as radiotherapy, radiofrequency ablation, and cryoablation, have been used with variable success and limited follow up. Medical management is warranted both prior to definitive therapy and in non-operable cases to improve symptoms and allow for bone remineralization. Oral phosphate and calcitriol were the mainstay of medical therapy, however, the development of burosumab, a monoclonal blocking antibody to FGF23, has introduced an approved therapy that improves hypophosphatemia and symptoms in patients with TIO. In select cases, cinacalcet can be an effective adjuvant to phosphate and calcitriol. Continued monitoring for tumor growth is necessary while on medical therapy. Infigratinib, a selective FGFR tyrosine-kinase inhibitor targeting a causative tumoral fusion protein, can reverse the biochemical findings of TIO and possibly reduce tumor mass; however, its use is constrained by serious side effects. Overall, innovations in medical and interventional treatments have broadened therapeutic options for patients with PMTs, particularly in cases where a curative surgical resection is not possible.

Large-cell Basaloid Adenocarcinoma of the Lung: A Clinicopathologic Study of 12 Cases of a Distinctive Form of Lung Cancer Often Mistaken for Large-cell Neuroendocrine Carcinoma

A distinctive form of lung adenocarcinoma that closely mimics large-cell neuroendocrine carcinoma is described. The tumors arose in 6 women and 6 men aged 46-86 years (mean=58.4). They presented as peripheral subpleural masses measuring 2-12 cm (mean=6.5 cm). Histologically they were characterized by islands or anastomosing and serpiginous strands of large, atypical cells showing striking peripheral palisading of nuclei, with high mitotic activity and prominent comedo-like areas of necrosis. Because of the striking resemblance to neuroendocrine tumors, some of the cases were initially diagnosed as large-cell neuroendocrine carcinoma despite the absence of neuroendocrine markers. Immunohistochemistry showed positivity of the tumor cells for TTF1 and napsin-A, and negative staining for p40. The tumors were also uniformly negative for multiple neuroendocrine markers, including chromogranin, synaptophysin, CD56, and INSM1. Electron microscopy performed in 2 cases was negative for membrane-bound dense core neurosecretory granules. Pathogenic alterations were detected in 5 of 8 tumors tested by next-generation sequencing. Point mutations in KRAS and TP53 were identified in 5 patients. Low-level amplification of GNAS , KIT , and FGFR1 was present in 2 patients. No RB1 mutations were identified. Clinical follow-up in 10 cases showed that 2 patients died of their tumors, 2 experienced distant metastases, and 6 were alive and well from 1 to 13 years after diagnosis (median=7.1 y). Large-cell basaloid adenocarcinoma is an unusual variant of lung cancer that is easily confused with large-cell neuroendocrine carcinoma. Awareness of this unusual variant of lung adenocarcinoma is important for treatment and prognosis and for avoiding misdiagnosis.

Primary Intraosseous Solitary Fibrous Tumor of the Mandible: Report of a Diagnostically Challenging Case with NAB2::STAT6 Fusion and Review of the Literature

INTRODUCTION

Solitary fibrous tumor (SFT) represents an uncommon mesenchymal neoplasm affecting primarily the extremities and deep soft tissues with, overall, benign but locally aggressive biologic behavior and an underlying pathognomonic NAB2::STAT6 fusion. Intraosseous SFTs are infrequent, and involvement of the jawbones is exceedingly rare.

CASE PRESENTATION

A 54-year-old woman presented with an asymptomatic, well-demarcated, multilocular radiolucency of the left posterior mandible featuring focally irregular borders, root resorption and lingual cortex perforation. The lesion had shown progressive growth over a 6-year period. Microscopically, a proliferation of predominantly ovoid and spindle-shaped cells with indistinct cell membrane borders, elongated, plump or tapered, hyperchromatic nuclei, and lightly eosinophilic cytoplasm was noted. Marked cytologic atypia, pleomorphism and mitoses were absent. A secondary population of epithelioid cells exhibiting ovoid or elongated vesicular nuclei, and abundant, pale eosinophilic or vacuolated cytoplasm was also present. The supporting stroma was densely fibrous with areas of marked hyalinization and variably-sized, ramifying, thin-walled vessels. By immunohistochemistry, lesional cells were strongly and diffusely positive for STAT6 and CD99, and focally immunoreactive for MDM2 and SATB2. Ki-67 was expressed in less than 5% of lesional cells, while most interspersed epithelioid cells were positive for the histiocyte marker, CD163. Molecular analysis disclosed a NAB2::STAT6 fusion confirming the diagnosis of SFT. The patient underwent segmental mandibulectomy.

CONCLUSIONS

Herein, we report the first case of primary intraosseous SFT of the mandible with complete documentation of its characteristic immunohistochemical and molecular features. Diagnosis of such unusual presentations may be further complicated by the challenging histomorphologic diversity of SFT.

GRM1-Rearranged Chondromyxoid Fibroma With FGF23 Expression: A Potential Pitfall in Small Biopsies

The clinical, radiological, and histopathological features of chondromyxoid fibroma can sometimes resemble those of other benign or malignant tumors. Recently, recurrent GRM1 rearrangements have been identified in chondromyxoid fibroma, and GRM1 positivity by immunohistochemistry has emerged as a dependable surrogate marker for this molecular alteration. Phosphaturic mesenchymal tumor is a rare tumor that often exhibits overexpression of fibroblastic growth factor 23 (FGF23) through various mechanisms. In this report, we present a case of GRM1-rearranged chondromyxoid fibroma that also exhibited FGF23 expression via in situ hybridization, posing significant diagnostic challenges during workup of the initial core biopsy. We hope that this case can serve as an educational resource, shedding light on a rare diagnostic pitfall.

G, Surendran S, Patinharayil G, Fazil V.V. M, K.V. N, Sudhan S. R. PTH like substance secreting mesenchymal tumor causing oncogenic osteomalacia; unravelling the difficulties in localization - A report of 2 cases

Background

Oncogenic osteomalacia is a rare paraneoplastic association of Phosphaturic mesenchymal tumor (PMT) secreting excessive levels of a PTH like substance. They usually remain undiagnosed and patients suffer for years. The rarity of this tumor and its non-specific clinical presentations poses great challenge to the treating surgeons. Its management is poorly described in literature. We report two of such rare cases without much diagnostic delay.

Case report

We had 2 cases; A 53-year-old south east Asian male with 6 months of debilitating pain over multiple sites, and another 44-year-old male patient with complaints of low back ache, and pain over both lower and upper limbs for 1.5 years. Both had low serum phosphorus and elevated FGF-23 values, but all other parameters were normal. A PMT was suspected and confirmed on a Ga68- DOTATOC scan in both cases, and on complete excision, their symptoms and the altered blood parameters got normalized. Histology was consistent with PMT.

Conclusion

Accurate and timely diagnosis of a PMT with non-specific features are extremely challenging, but not without solutions. Even though a tumor of rarity, with the appropriate imaging modalities like Ga68- DOTATOC scan, and estimation of FGF-23 and serum phosphorus levels, they can be diagnosed. Once identified, complete removal is often curative within a few months.

Comprehensive Molecular Characterization of a Large Series of Calcified Chondroid Mesenchymal Neoplasms Widening Their Morphologic Spectrum

Recently, FN1 fusions to receptor tyrosine kinase genes have been identified in soft tissue tumors with calcified chondroid matrix named calcifying chondroid mesenchymal neoplasms (CCMNs). We collected 33 cases of CCMN from the French network for soft tissue and bone tumors. We performed whole-exome RNA sequencing, expression analysis, and genome-wide DNA methylation profiling in 33, 30, and 20 cases of CCMN compared with a control group of tumors, including noncalcified tenosynovial giant cell tumor (TGCT). Among them, 15 cases showed morphologic overlap with soft tissue chondroma, 8 cases with tophaceous pseudogout, and 10 cases with chondroid TGCT. RNA-sequencing revealed a fusion of FN1 in 76% of cases (25/33) with different 5' partners, including most frequently FGFR2 (14 cases), TEK or FGFR1. Among CCMN associated with FGFR1 fusions, 2 cases had overexpression of FGF23 without tumor-induced osteomalacia. Four CCMN had PDGFRA::USP8 fusions; 3 of which had histologic features of TGCT and were located in the hip, foot, and temporomandibular joint (TMJ). All cases with FN1::TEK fusion were located at TMJ and had histologic features of TGCT with or without chondroid matrix. They formed a distinct cluster on unsupervised clustering analyses based on whole transcriptome and genome-wide methylome data. Our study confirms the high prevalence of FN1 fusions in CCMN. In addition, through transcriptome and methylome analyses, we have identified a novel subgroup of tumors located at the TMJ, exhibiting TGCT-like features and FN1::TEK fusions.

Inflammatory myofibroblastic tumor in a patient with X-Linked hypophosphatemia: A case of Occam's razor or Hickam's dictum?

We present the case of a patient with X-Linked Hypophosphatemia (XLH) and an inflammatory myofibroblastic tumor (IMT) of the bladder which prompted further investigation into the possible relationship between XLH and IMT i.e. a case of Occam's Razor or Hickam's Dictum?

Superficial acral calcified chondroid mesenchymal neoplasm harboring an FN1::FGFR2 fusion and review of the literature

Calcified chondroid mesenchymal neoplasm is a recently recognized bone and soft tissue entity primarily found in the extremities and the temporomandibular joint. This neoplasm is typically driven by the fusion of the FN1 gene with a kinase. In this case report, we provide a detailed account of a rare superficial calcified chondroid mesenchymal neoplasm located on the left big toe, characterized by an FN1::FGFR2 fusion. The tumor exhibited a peripheral collarette and consisted of large intradermal histiocytoid to epithelioid cells with no mitotic activity. These cells displayed fine chromatin and abundant pale eosinophilic cytoplasm, forming a swirling syncytium. They were interspersed with localized areas of glassy chondromyxoid matrix containing randomly mineralized calcific material and isolated osteoclast-like giant cells. RNA sequencing confirmed the presence of an FN1 (exon 29)::FGFR2 (exon 7) gene fusion. Our report emphasizes the importance for dermatopathologists to consider this entity when evaluating superficial lesions displaying mesenchymal, chondroid, and calcified attributes.

Treatment and Diagnose of Spinal Phosphaturic Mesenchymal Tumor: A Case Report and a Systematic Literature Review

BACKGROUND

Spinal phosphaturic mesenchymal tumor (PMT) is a rare disorder but can be cured once the diagnosis is clear and a complete removal by surgery is performed. To the best of our knowledge, only 22 cases in the spine have been described, and we report a case with the largest number of spinal segments (T12-L5) affected among spine PMT cases.

METHODS

A comprehensive literature search was performed until May 23, 2023, following the Preferred Reporting Items for Systematic Reviews guidelines. Studies were chosen through relevant PubMed, Web of Science, and EMBASE searches to prioritize obtaining the largest studies. The Medical Subject Headings and Boolean operators employed for this search were ("PMT" or "TIO" or "Tumor-induced osteomalacia" or "phosphaturic mesenchymal tumor") and ("spine" or "spinal"). Two researchers (L.S.Z. and D.B.C) independently reviewed and evaluated the included articles. Any differing opinions were discussed until a consensus was reached. A total of 18 studies were included. A case report is also presented.

RESULTS

We report a case of spinal PMT. The full text of the relevant articles was construed. A total of 18 studies were reviewed and consolidated. These articles are roughly divided into the following 5 subcategories: 1) clinical features and baseline distribution, 2) laboratory and imaging findings, 3) pathological manifestations, and 4) surgical methods and treatment options.

CONCLUSIONS

Spinal PMT is very rare with a high rate of misdiagnosis and debilitating complications, so it is of significance to increase awareness of the disease among spine surgeons consulted by patients with spinal PMT. 68Ga-DOTATOC-PET/CT shows very high sensitivity to the spinal PMT but there is no way to exactly determine the location of the tumor. PMT has unique immunohistochemical characteristics and malignant PMT is rare. Once diagnosed, complete surgical excision is the recommended treatment. Burosumab is one of the available options, especially in cases that are recurrent and difficult to surgically resect.

Phosphaturic mesenchymal tumor: Clinicopathological features with outcomes in 10 patients with review of literature

BACKGROUND

Phosphaturic mesenchymal tumors (PMTs) are rare mesenchymal tumors, associated with long-standing, non-specific but often debilitating symptoms in the affected patients. These tumors display characteristic histopathological features and in case, identified timely, can be a boon for patients, given an excision is completely curative.

AIMS

To evaluate the clinical and histopathological features of 10 PMTs, diagnosed at our institution, along with clinical outcomes in those patients.

MATERIALS AND METHODS

This was a retrospective study, wherein 10 PMTs, diagnosed from January 2013 to July 2022, were included.

RESULTS

The average age at the time of diagnosis was 40 years with an M:F ratio of 4:1. Clinical features included lumps, weakness, bone pain, difficulty in moving and walking, and pathologic fractures. The biochemical analysis showed normal serum calcium levels (average = 9.5 mg/dL), with low serum phosphorus (average = 2.2 mg/dL) and raised serum fibroblast growth factor 23 (FGF23) levels, in all the cases, wherever available. On histopathology, all tumors showed cells arranged in a hemangiopericytomatous pattern, including oval to short spindle forms. Multinucleate giant cells were present in nine tumors, and characteristic "grungy calcifications" was observed in eight tumors. Prominent pseudo cystic spaces were seen in eight tumors. A significant number of mitotic figures and tumor necrosis were not seen in any tumor. In five cases where follow-up was available, there was complete resolution of symptoms post-resection with no recurrence or metastasis. All those patients were free of disease until the last follow-up.

CONCLUSION

This constitutes the first largest comprehensive study on these rare tumors from our country. PMTs can be diagnosed based on certain histopathological features and correlation with clinicoradiological and biochemical findings. These are invariably benign neoplasms. Patients are relieved of their debilitating symptoms after adequate surgical tumor resection. Therefore, their correct and timely diagnosis is crucial.

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.

International Consensus Statement on Allergy and Rhinology: Sinonasal Tumors

BACKGROUND

Sinonasal neoplasms, whether benign and malignant, pose a significant challenge to clinicians and represent a model area for multidisciplinary collaboration in order to optimize patient care. The International Consensus Statement on Allergy and Rhinology: Sinonasal Tumors (ICSNT) aims to summarize the best available evidence and presents 48 thematic and histopathology-based topics spanning the field.

METHODS

In accordance with prior International Consensus Statement on Allergy and Rhinology documents, ICSNT assigned each topic as an Evidence-Based Review with Recommendations, Evidence-Based Review, and Literature Review based on the level of evidence. An international group of multidisciplinary author teams were assembled for the topic reviews using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses format, and completed sections underwent a thorough and iterative consensus-building process. The final document underwent rigorous synthesis and review prior to publication.

RESULTS

The ICSNT document consists of four major sections: general principles, benign neoplasms and lesions, malignant neoplasms, and quality of life and surveillance. It covers 48 conceptual and/or histopathology-based topics relevant to sinonasal neoplasms and masses. Topics with a high level of evidence provided specific recommendations, while other areas summarized the current state of evidence. A final section highlights research opportunities and future directions, contributing to advancing knowledge and community intervention.

CONCLUSION

As an embodiment of the multidisciplinary and collaborative model of care in sinonasal neoplasms and masses, ICSNT was designed as a comprehensive, international, and multidisciplinary collaborative endeavor. Its primary objective is to summarize the existing evidence in the field of sinonasal neoplasms and masses.

Expanding the spectrum of tyrosine kinase fusions in calcified chondroid mesenchymal neoplasms: Identification of a novel PDGFRA::USP8 gene fusion

Calcified chondroid mesenchymal neoplasms represent a distinct, and recently recognized, spectrum of tumors. To date most cases have been reported to be characterized by FN1 gene fusions involving multiple potential tyrosine kinase partners. Following incidental identification of a tumor morphologically corresponding to calcified chondroid mesenchymal neoplasm, but with a PDGFRA::USP8 gene fusion, we undertook a retrospective review to identify and characterize additional such cases. A total of four tumors were identified. Each was multilobulated and composed of polygonal-epithelioid-stellate cells with a background of chondroid matrix containing distinctive patterns of calcification. Targeted RNA sequencing revealed an identical PDGFRA (exon 22)::USP8 (exon 5) gene fusion in each case. Subsequent immunohistochemical staining confirmed the presence of PDGFRα overexpression. In summary, we report a series of four tumors within the morphologic spectrum of calcified chondroid mesenchymal neoplasms. In contrast to prior reports, these tumors harbored a novel PDGFRA::USP8 gene fusion, rather than FN1 rearrangement. Our findings expand the molecular diversity of these neoplasms, and suggest they are united through activation of protein kinases.

Transformation of a long-standing phosphaturic tumor-inducing osteomalacia into malignancy

Key Clinical Message

Tumor-induced osteomalacia is a paraneoplastic syndrome characterized by renal phosphate wasting and deranged bone turnover. Clinicians should consider tumor-induced osteomalacia in unexplained hypophosphatemia and investigate for underlying tumors.

Abstract

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by renal phosphate wasting, which leads to deranged bone turnover. TIO is usually associated with benign mesenchymal tumors, although it has also been reported in malignant tumors. We present the case of a 56-year-old individual who experienced a protracted 6-year clinical course characterized by hypophosphatemia, weakness, and kyphosis, alongside the presence of a foot tumor. Subsequently, this lesion displayed malignant behavior and was ultimately diagnosed as a high-grade sarcoma. To date, this case is among the 10 reported cases in the literature of a mesenchymal tumor associated with TIO undergoing malignant transformation. This report underscores the importance of a comprehensive evaluation of patients with unexplained hypophosphatemia and highlights the need for diligent follow-up to detect possible malignant transformation of the underlying tumor. Clinicians should consider TIO in the differential diagnosis of hypophosphatemia and promptly investigate for the presence of an underlying tumor, as early detection may improve the patient's prognosis.

Klotho Overexpression Is Frequently Associated With Upstream Rearrangements in Fusion-Negative Phosphaturic Mesenchymal Tumors of Bone and Sinonasal Tract

Phosphaturic mesenchymal tumors (PMT) are uncommon neoplasms that cause hypophosphatemia/osteomalacia mainly by secreting fibroblast growth factor 23. We previously identified FN1::FGFR1/FGF1 fusions in nearly half of the PMTs and frequent KL (Klotho or α-Klotho) overexpression in only those with no known fusion. Here, we studied a larger cohort of PMTs for KL expression and alterations. By FN1 break-apart fluorescence in situ hybridization (FISH) and reappraisal of previous RNA sequencing data, 6 tumors previously considered "fusion-negative" (defined by negative results of FISH for FN1::FGFR1 fusion and FGF1 break-apart and/or of RNA sequencing) were reclassified as fusion-positive PMTs, including 1 containing a novel FN1::ZACN fusion. The final cohort of fusion-negative PMTs included 33 tumors from 32 patients, which occurred in the bone (n = 18), soft tissue (n = 10), sinonasal tract (n = 4), and brain (n = 1). In combination with previous work, RNA sequencing, RNA in situ hybridization, and immunohistochemistry showed largely concordant results and demonstrated KL/α-Klotho overexpression in 17 of the 28 fusion-negative and none of the 10 fusion-positive PMTs studied. Prompted by a patient in this cohort harboring germline KL upstream translocation with systemic α-Klotho overexpression and multifocal PMTs, FISH was performed and revealed KL rearrangement in 16 of the 33 fusion-negative PMTs (one also with amplification), including 14 of the 17 cases with KL/α-Klotho overexpression and none of the 11 KL/α-Klotho-low fusion-negative and 11 fusion-positive cases studied. Whole genomic sequencing confirmed translocation and inversion in 2 FISH-positive cases involving the KL upstream region, warranting further investigation into the mechanism whereby these rearrangements may lead to KL upregulation. Methylated DNA immunoprecipitation and sequencing suggested no major role of promoter methylation in KL regulation in PMT. Interestingly, KL-high/-rearranged cases seemed to form a clinicopathologically homogeneous group, showing a predilection for skeletal/sinonasal locations and typically matrix-poor, cellular solitary fibrous tumor-like morphology. Importantly, FGFR1 signaling pathways were upregulated in fusion-negative PMTs regardless of the KL status compared with non-PMT mesenchymal tumors by gene set enrichment analysis, perhaps justifying FGFR1 inhibition in treating this subset of PMTs.

Phosphaturic mesenchymal tumor: A chondromyxoid fibroma-like type

Phosphaturic mesenchymal tumor (PMT) is a rare neoplasm that causes tumor-induced osteomalasia (TIO) in most affected patients, usually through the production of fibroblast growth factor 23 (FGF23). This tumor is often misdiagnosed due to its relative rarity and its widely varied histomorphologic spectrum. Here we describe a case of a 78-year-old woman who presented with a left middle tumor without symptoms of TIO. The histological features resembled chondromyxoid fibroma with smudgy calcification in the tumor matrix. In addition, we evaluated FGF23 expression through immunohistochemical study and reverse transcription polymerase chain reaction. PMT with chondromyxoid fibroma features are extremely rare. Examining the expression of FGF23 is useful in the diagnosis of PMT.

Phosphaturic Mesenchymal Tumors with or without Phosphate Metabolism Derangements

Phosphaturic mesenchymal tumors (PMT) are rare neoplasms, which can give rise to a multifaceted syndrome, otherwise called tumor-induced osteomalacia (TIO). Localizing these tumors is crucial to obtain a cure for the phosphate metabolism derangement, which is often the main cause leading the patient to seek medical help, because of invalidating physical and neuromuscular symptoms. A proportion of these tumors is completely silent and may grow unnoticed, unless they become large enough to produce pain or discomfort. FGF-23 can be produced by several benign or malignant PMTs. The phosphate metabolism, radiology and histology of these rare tumors must be collectively assessed by a multidisciplinary team aimed at curing the disease locally and improving patients' quality of life. This narrative review, authored by multiple specialists of a tertiary care hospital center, will describe endocrine, radiological and histological features of these tumors, as well as present surgical and interventional strategies to manage PMTs.

[Special mesenchymal neoplasms of the head and neck: Update from the 2022 WHO]

Similar to the approach adopted in the classification of tumors in other organs, a new feature of the current Word Health Organization (WHO) classification of the head and neck tumors is the exclusion of soft tissue tumors from single organs and their inclusion in a separate chapter devoted to them. This applies to tumors that are principally ubiquitous but show a predilection for the head and neck sites. The only exception to this rule represents those entities that are almost restricted to a specific head and neck site/organ (such as nasopharyngeal angiofibroma, sinonasal glomangiopericytoma, and biphenotypic sinonasal sarcoma), which remain in their respective organ chapters. Included among soft tissue tumors are some old but still underrecognized entities, such as phosphaturic mesenchymal tumors, and newly defined entities, such as GLI1-altered tumors. The aim of including these entities is to enhance recognition of these uncommon but likely under-recognized entities to better characterize them in the future. This review summarizes the main features of these rare entities and discusses their differential diagnoses.

Calcified Chondroid Mesenchymal Neoplasm: Exploring the Morphologic and Clinical Features of an Emergent Entity With a Series of 33 Cases

Calcified chondroid mesenchymal neoplasm is a term proposed for tumors with a spectrum of morphologic features, including cartilage/chondroid matrix formation, that frequently harbor FN1 gene fusions. We report a series of 33 cases of putative calcified chondroid mesenchymal neoplasms, mostly referred for expert consultation out of concern for malignancy. Patients included 17 males and 16 females, with a mean age of 51.3 years. Anatomic locations include the hands and fingers, feet and toes, head and neck, and temporomandibular joint; 1 patient presented with multifocal disease. Radiologic review showed soft tissue masses with variable internal calcification, which occasionally scalloped bone but in all cases appeared indolent/benign. Tumors had a mean gross size of 2.1 cm and a homogenous rubbery to fibrous/gritty tan-white cut surface. Histology demonstrated multinodular architecture with a prominent chondroid matrix and increased cellularity towards the periphery of the nodules. The tumor cells were polygonal with eccentric nuclei and bland cytologic features and showed a variable amount of increased spindled / fibroblastic forms in the perinodular septa. The majority of cases had notable grungy and/or lacy calcifications. A subset of cases demonstrated at least focal areas of increased cellularity and osteoclast-like giant cells. Herein, we confirm the distinct morphologic and clinicopathologic features associated with this entity with the largest series to date, with a focus on practical diagnostic separation from similar chondroid neoplasms. Awareness of these features is critical in avoiding pitfalls, including a malignant diagnosis of chondrosarcoma.

Unexpected Phosphaturic Mesenchymal Tumor of the Femoral Head

Osteonecrosis of femoral head (ONFH) is clinically common and easily diagnosed via imaging examination, especially when there is a definite cause, such as a fracture, long-term hormonotherapy, etc. However, some rare neoplastic lesions of the femoral head can mimic its image performance in some situations, leading to misdiagnosis. We present the case of a 57-year-old male with bone pain in the left hip joint that persisted for 2 years. CT and MRI images were performed and both were suggestive of ONFH. Unexpectedly, the histopathologic results of left proximal femur resection revealed the diagnosis of phosphaturic mesenchymal tumor (PMT), a rare mesenchymal tumor. His hip pain was obviously relieved after surgery, and the course of 1-year follow-up was uneventful.

Phosphaturic Mesenchymal Tumors: Rethinking the Clinical Diagnosis and Surgical Treatment

BACKGROUND

The diagnosis of phosphaturic mesenchymal tumors (PMT) is easily delayed clinically, and their surgical treatment is unstandardized. This study aimed to evaluate our experience in the diagnosis and treatment of PMT and provide a research basis for the accurate and standardized treatment of PMT.

MATERIALS AND METHODS

Twelve patients diagnosed with PMT in our department and who underwent surgical treatment were included in this study. Preoperative demographic and clinical information were recorded. CT, MRI, and technetium-99m (Tc99m)-octreotide PET/CT imaging techniques were used to evaluate the general conditions and lesion boundaries of the tumors. Surgical treatment was performed using radical resection and microwave ablation-assisted extended curettage according to the lesion location and size. Patients were strictly followed up with and evaluated for oncological prognosis, radiological results, bone healing, serum ion levels, limb function, and pain level; the occurrence of complications was also recorded.

RESULTS

Three patients underwent radical resection, and nine underwent microwave ablation-assisted extended curettage. The average duration of symptoms in this group was 1.5 years (9-35 months) before diagnosis. Serum phosphate and AKP levels returned to normal one and two weeks postoperatively, respectively. There was no apparent specificity in the pathological findings; however, the immunohistochemistry of FGF-23 was positive, and the original fracture sites were effectively healed during the follow-up. The limb function and pain scores were significantly improved. The MSTS score increased from 15.3 to 29.0, and the VAS score decreased from 5.3 to 0.4. All patients recovered, and 90% resumed their original jobs.

CONCLUSIONS

Accurate diagnosis and standardized surgical treatment are crucial to achieving a clinical cure for PMT. Combining clinical manifestations, biochemical examinations, imaging characteristics, and pathological findings is an effective way to diagnose PMT accurately. Radical resection and microwave ablation-assisted extended curettage are reliable surgical treatment methods for PMT.

Tumor-induced osteomalacia treated with T12 tumor resection

Summary

Tumor-induced osteomalacia (TIO) is a rare form of osteomalacia caused by fibroblast growth factor-23 (FGF23)-secreting tumors. Most of these tumors are phosphaturic mesenchymal tumors (PMTs) typically involving soft tissue in the extremities and bone of the appendicular skeleton and cranium. We report the case of a 60-year-old woman with about 3 years of persistent bone pain and multiple fractures, initially diagnosed as osteoporosis, who was found to have hypophosphatemia with low 1,25-dihydroxyvitamin D and elevated alkaline phosphatase and inappropriately normal FGF23 consistent with TIO. Her symptoms improved with phosphate supplementation, vitamin D and calcitriol. 68Ga-DOTATATE imaging revealed a T12 vertebral body lesion confirmed on biopsy to be a PMT. She underwent resection of the PMT with resolution of TIO and increased bone density. This rare case of TIO secondary to a PMT of the thoracic spine highlights some of the common features of PMT-associated TIO and draws attention to PMT-associated TIO as a possible cause of unexplained persistent bone pain, a disease entity that often goes undiagnosed and untreated for years.

Learning points

Tumor-induced osteomalacia (TIO) is typically caused by phosphaturic mesenchymal tumors (PMTs) that are usually found in the soft tissue of the extremities and bone of the appendicular skeleton/cranium and rarely in the spine. TIO may be misdiagnosed as osteoporosis or spondyloarthritis, and the correct diagnosis is often delayed for years. However, osteoporosis, in the absence of fracture, is not associated with bone pain. The hallmark of TIO is hypophosphatemia with inappropriately normal or low 1,25-dihydroxyvitamin D and elevated or inappropriately normal fibroblast growth factor-23 (FGF23) levels. In patients with unexplained persistent bone pain, a serum phosphate should be measured. Consider PMT-associated TIO as a potential cause of unexplained persistent bone pain and hypophosphatemia. PMTs express somatostatin receptors and may be identified with 68Ga-DOTATATE imaging. Complete surgical resection is the preferred treatment for spinal PMTs associated with TIO.

Phosphaturic mesenchymal tumor in right thigh: 2 cases report and literature review

Background

Phosphaturic mesenchymal tumor (PMT) is a very rare tumor of bone and soft tissue that has no specific clinical manifestations. Here we present 2 cases of PMT in the right thigh, including comparatively adequate immunohistochemistry.

Case Presentation

We described 2 cases of PMT in the right thigh with manifestations of hypophosphatemia. PET-CT examination showed that both patients had lesions with increased expression of somatostatin receptors in the right thigh. Bland cells and dirty calcified stroma were exhibited under the microscope. And immunohistochemical detection of FGF-23 was positive.

Conclusions

PMT is a very uncommon tumor for which diagnosis and treatment are often delayed. Considering the importance of surgery for the treatment of this disease, a full understanding of its clinicopathological features will facilitate the diagnosis of this disease.

Dorsal vertebral body tumor and non-compressive quadriparesis – A rare case report of a phosphaturic mesenchymal tumor

Background:

Phosphaturic mesenchymal tumors cause renal phosphate wasting leading to hypophosphatemia manifesting as bone pain and fractures. About 95% of these tumors involve the extremities and the appendicular skeleton, with spinal tumors being exceedingly rare. We describe a case of non-compressive quadriparesis, caused by a thoracic vertebral body phosphaturic mesenchymal tumor (PMT).

Case Description:

A 34-year-old gentleman presented with a 3-year history of gradually progressive quadriparesis, predominantly involving proximal muscles. Magnetic resonance imaging neither showed evidence of compressive lesions nor myelopathy. On routine biochemistry, he was found to have hypophosphatemia and phosphaturia, with serum phosphorus levels of 1.84 mg/dl, and fractional excretion of phosphorus >5%. A DOTATOC positron emission tomography scan suggested the possibility of a PMT in the D10 vertebral body with a corresponding hyperdense/sclerotic focus on non-contrast computed tomography. After instituting phosphate replacement therapy and complete surgical excision of the hyperdense focus, he made a full neurological recovery. His phosphate levels normalized without the need for supplements. Histopathological examination showed spindle cells with positive staining for Vimentin, a mesenchymal cell marker. At 5 years of follow-up, the patient continues to be asymptomatic with a full return to normal function and no residual weakness.

Conclusion:

PMTs involving the spine are a rare reversible cause of non-compressive quadriparesis. Early diagnosis and excision of the lesion correct the hypophosphatemia and result in complete neurological recovery.

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

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

Tumor-induced osteomalacia characterized by "painful knee joint with difficulty in moving": a case report

BACKGROUND

Tumor-related osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by severe hypophosphatemia and osteomalacia. The diagnosis of TIO can be very difficult because of its nonspecific nature of clinical manifestations. Here we reported a case of young TIO patient with "painful knee joint with difficulty in moving" to improve the clinical diagnosis and treatment levels.

CASE PRESENTATION

The patient's clinical features were consistent with TIO. A tumor was successfully located in left tibial by ⁶⁸Ga-DOTATATE PET/CT, and then was surgically resected. Upon pathologic assessment, the tumor was diagnosed as phosphaturia stromal tumor (PMT) with positive Vim staining. After the surgery, serum phosphate level rapidly recovered and symptoms significantly improved.

CONCLUSION

TIO should be considered in patients with chronically hypophosphorus osteomalacia in the setting of no family history. Early removal of the responsible tumors is clinically essential for the treatment, and imaging examination is of great significance for tumor localization.

Persistence and recurrence in tumor-induced osteomalacia: A systematic review of the literature and results from a national survey/case series

PURPOSE

Tumor induced osteomalacia (TIO) is a rare disease of mineral metabolism, whose clinical picture is dominated by hypophosphatemia usually due to an excess of circulating FGF23 produced by small mesenchymal tumors. Data on the real prevalence of the disease are lacking, with the knowledge of the disease mainly relying on case reports and small case series. No estimate is available on the prevalence of uncured TIO.

METHODS

National multi-center, cross-sectional and retrospective study on persistent or recurrent cases of TIO followed in referral centers for bone diseases; systematic review of the published persistent and recurrent cases of TIO. Data from patients consecutively evaluated in referral Italian centers for bone diseases were collected; a PubMed search on persistent, recurrent and unoperable cases of TIO was carried out.

RESULTS

Sixteen patients (mean age at diagnosis 52.5 ± 10.6 years) with persistent (n = 6, 37,5%), recurrent (n = 7, 43.7%) or not operable (n = 3, 18.8%) TIO were described. Delay in diagnosis (2.5 ± 1.3 years) was demonstrated. All patients experienced fragility fractures or pseudofractures and disabling bone and muscle pain. BMD was significantly reduced (mean T-score -2.7 ± 1.7 and -2.7 ± 0.9 at lumbar spine and femoral neck, respectively). Fourteen patients were maintained under therapy with phosphate salts and calcitriol, while in 2 patients therapy with burosumab, an anti-FGF23 antibody, was commenced.

CONCLUSION

A significant number of patients with TIO remain either undiagnosed for tumor localization or tumor recur or persist after surgery. These patients with active disease represent possible candidates for burosumab treatment.

Diagnostic Utility of Somatostatin Receptor 2A Immunohistochemistry for Tumor-induced Osteomalacia

CONTEXT

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic disorder caused by excessive fibroblast growth factor 23 (FGF23) secretion. FGF23 immunohistochemistry (IHC) is proposed as a useful adjunctive marker to confirm TIO diagnosis. However, it often stains focally, limiting its diagnostic utility.

OBJECTIVE

This work aimed to compare the diagnostic performance between somatostatin receptor 2A (SSTR2A) and FGF23 IHC for TIO.

METHODS

We retrospectively reviewed TIO-diagnosed patients in Severance Hospital between July 2006 and May 2020. Histologic evaluation was performed using histoscore (H score) (expression area proportion score [0-2] × intensity score [1-3], [total, 0-6]). FGF23 and SSTR2A IHC were performed using unstained slides from 18 localized TIO patients and 9 and 15 non-TIO controls with bone and soft-tissue tumors, respectively. SSTR2A positivity was defined as cytoplasmic, membranous, or Golgi staining in more than 1% of tumor cells, and negativity as nonspecific nuclear staining. FGF23 positivity was defined as cytoplasmic expression in more than 1% of the tumor area and negativity as nonspecific nuclear staining.

RESULTS

Suspicious lesions were successfully detected in 14 of 15 patients who underwent 68Ga-DOTATOC scans. Diffuse cytoplasmic SSTR2A expression was identified in all TIO patients and focal weak nuclear staining in 12 of 15 controls. FGF23 cytoplasmic expression was identified in 11 of 18 TIO patients and diffuse nuclear staining in 9 of 9 controls. The H score was higher in SSTR2A than in FGF23 IHC (median [interquartile range]: 6 [6-6] vs 1 [0-2], P < .001).

CONCLUSION

SSTR2A IHC with H-score quantification might be a more sensitive, adjunctive diagnostic tool than FGF23 IHC for TIO diagnosis.

Phosphaturic Mesenchymal Tumors in the Head and Neck Demonstrate a Broad Clinical and Morphologic Spectrum

Phosphaturic mesenchymal tumour (PMT) is a rare tumour that occurs in bone or soft tissue and is associated with production of fibroblast growth factor 23 (FGF23) leading to tumor-induced osteomalacia. We report three cases of PMT involving the head and neck that highlight the broad spectrum of clinical and histologic features of PMT. One of these lesions from the hard palate demonstrated an admixture of epithelial and mesenchymal elements, a feature that can pose a diagnostic challenge. The diagnostic utility of immunohistochemistry including FGF23, somatostatin receptor 2A, SATB2, ERG and CD56 is discussed. The biochemical pathway in the development of PMT associated tumor induced osteomalacia and its role in investigations and management of PMT is also described.

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.

Phosphaturic mesenchymal tumors: radiological aspects and suggested imaging pathway

Phosphaturic mesenchymal tumors (PMTs) are rare mesenchymal neoplasms of soft tissue or bone origin that can give rise to a challenge in diagnostic imaging. These tumors are frequently associated with tumor-induced osteomalacia, also called oncogenic osteomalacia, which is a rare paraneoplastic syndrome characterized by ectopic secretion of fibroblast growth factor 23, a hormone that regulates serum phosphate level. PMTs show polymorphic features on both radiological findings and histological examination, causing problems in diagnosis owing to their similarity with other mesenchymal tumors. Thus, this paper aims to describe radiological aspects of PMTs and suggest an imaging pathway for accurate diagnosis throughout the evidence from the literature review.

Phosphaturic Mesenchymal Tumors of the Sinonasal Area and Skull Base: Experience at a Single Institution

OBJECTIVES

Phosphaturic mesenchymal tumor (PMT) is a rare, polymorphous neoplasm with a highly variable presentation and natural history and unpredictable clinical course. The primary objective was to describe our clinical experience with and management of 4 markedly different cases of sinonasal and skull base PMT.

METHODS

A retrospective case series with chart review, and relevant literature review, was performed at a tertiary academic medical center between 1998 and 2020. Adult patients treated for PMTs of the sinonasal area and skull base were included. Our main outcome measures included postoperative laboratory findings and radiological evidence of disease remission.

RESULTS

Four patients (2 Males, 2 Females; Mean Age: 63.5 years) with PMTs of the skull base have been managed at our institution since 1998. Patient presentations varied, ranging from severe phosphorus wasting and osteoporosis to symptoms secondary to mass effect, including nasal obstruction and rhinorrhea. All 4 patients were eventually found to have elevated levels of fibroblast growth factor 23. Tumors were located in the sinonasal area (right frontal sinus, right ethmoid sinus, and right nasal cavity, respectively) in 3 patients and in the lateral skull base (right jugular foramen) in 1 patient. All 4 patients underwent complete surgical resection of their tumors. PMT tissue pathology was confirmed in all cases. Gross total resection was achieved in all patients. There was no chemical or radiological evidence of disease recurrence in any patients at follow-up.

CONCLUSIONS

The presentation of skull base PMT is variable, and it may mimic other mass pathologies of the head and neck. Complete surgical resection with negative margins is potentially curative.

Clinical, morphological and immunohistochemical analysis of 13 cases of phosphaturic mesenchymal tumor - A holistic diagnostic approach

BACKGROUND

Phosphaturic mesenchymal tumor-mixed connective tissue (PMT-MCT) is a rare tumor characterized clinically by presence of tumor-induced osteomalacia (TIO), subsequent to elevated fibroblastic growth factor 23 (FGF23) levels. This study aims to analyse the morphological spectrum of PMT along with clinico-pathological correlation and immunophenotype profile of this rare tumor.

MATERIALS AND METHODS

Detailed histological analysis of all tumors presenting with TIO over past 7 years was done retrospectively. Immunohistochemistry was performed in all cases for SATB2, STAT6, CD34, FGF23, ERG, S100 and smooth muscle actin (SMA).

RESULTS

A total of 13 cases were analysed (8 female and 5 male) with mean age of 39.8 years. Five cases were arising from bone while 4 each from soft tissue and nasal cavity/paranasal sinus. All presented with hypophosphatemia, hyperphosphaturia, elevated serum FGF23 and features suggestive of osteomalacia. Histological examination revealed basophilic 'grungy' calcification seen in 7 (53.8%), osteoid formation in 8 (61.5%), chondroid matrix in 4 (30.8%), adipose tissue in 6 (46.2%), osteoclast-like giant cells in 9 (69.2%) and hemangiopericytomatous (HPC like) blood vessels in 7 cases (53.8%). HPC like vessels and adipose tissue were more common in nasal tumors while calcification was more common in tumors arising from bone. All cases showed immunoreactivity for SATB2 and clinical improvement following resection except one case with residual tumor.

CONCLUSION

PMT shows varied histological pattern with various matrix components depending on the site of the tumor. Serum FGF-23 is a useful adjunctive marker for diagnosis.

Calcified chondroid mesenchymal neoplasms with FN1-receptor tyrosine kinase gene fusions including FGFR2, FGFR1, MERTK, NTRK1, and TEK: a molecular and clinicopathologic analysis

Translocations involving FN1 have been described in a variety of neoplasms that share the presence of a cartilage matrix and may also contain a variable extent of calcification. Fusions of FN1 to FGFR1 or FGFR2 have been reported in nine soft tissue chondromas, mostly demonstrated indirectly by FISH analysis. Delineation of FN1 fusions with various partner genes will facilitate our understanding of the pathogenesis and diagnostic classification of these neoplasms. In this study, we present molecular, clinical, and pathologic features of 12 cartilaginous soft tissue neoplasms showing a predilection for the TMJ region and the distal extremities. We analyzed for gene fusions with precise breakpoints using targeted RNA-seq with a 115-gene panel. We detected gene fusions in ten cases, including three novel fusions, FN1-MERTK, FN1-NTRK1, and FN1-TEK, each in one case, recurrent FN1-FGFR2 fusion in five cases, FN1-FGFR1 in one case, and FGFR1-PLAG1 in one case. The breakpoints in the 5' partner gene FN1 ranged from exons 11-48, retaining the domains of a signal peptide, FN1, FN2, and/or FN3, while the 3' partner genes retained the transmembrane domain, tyrosine kinase (TK) domains, and/or Ig domain. The tumors are generally characterized by nodular/lobular growth of polygonal to stellate cells within a chondroid matrix, often accompanied by various patterns of calcification, resembling those described for the chondroblastoma-like variant of soft tissue chondroma. Additional histologic findings include extensive calcium pyrophosphate dihydrate deposition in two cases and features resembling tenosynovial giant cell tumor (TGCT). Overall, while the tumors from our series show significant morphologic overlap with chondroblastoma-like soft tissue chondroma, we describe findings that expand the morphologic spectrum of these neoplasms and therefore refer to them as "calcified chondroid mesenchymal neoplasms." These neoplasms represent a spectrum of chondroid/cartilage matrix-forming tumors harboring FN1-receptor TK fusions that include those classified as soft tissue chondroma as well as chondroid TGCT.

Prognostic Value of Positive Presurgical FDG PET/CT in the Evaluation of Tumor-Induced Osteomalacia

METHODS

Seventy-six patients who had surgically removed tumors that caused osteomalacia were included in this retrospective investigation. All patients underwent both 18F-FDG and 68Ga-DOTATATE PET/CT prior to surgery. The prognostic value of presurgical FDG PET/CT study was determined with 5-year follow-up.

RESULTS

In the presurgical evaluation, 68Ga-DOTATATE detected lesions in all 76 patients. However, FDG PET/CT was positive in only 25 among all 76 patients. Following surgical removal of the causative tumor, all 76 patients had symptomatic relief and normalization of the serum phosphate level initially. However, 15 of 76 cases (19.7%) had recurrent hypophosphatemia and became symptomatic again during the follow-up. Among these 15 patients with recurrence, 11 (73.3%) had recurrent lesions at the original location of the resected causative tumors, whereas 4 were in other locations due to malignant nature of the primary tumor. Interestingly, 14 of these 15 patients with recurrent disease had positive presurgical FDG PET/CT findings with an incident ratio of 56.0% (14 of 25). In contrast, only 1 patient with recurrent disease had negative presurgical FDG PET/CT scan with an incident ratio of 1.9% (1 of 51), significantly less than the positive presurgical FDG PET/CT group (P < 0.05).

CONCLUSIONS

A positive presurgical FDG PET/CT suggests increased likelihood for possible recurrence of TIO after surgical resection. In contrast, when a causative tumor detected by 68Ga-DOTATATE PET/CT does not have elevated activity on FDG PET/CT, the chance of recurrence is very small.

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.

Clinicopathologic and molecular features of six cases of phosphaturic mesenchymal tumor

Phosphaturic mesenchymal tumors (PMT) are rare neoplasms characterized by secretion of FGF23, resulting in renal phosphate wasting and osteomalacia. This tumor-induced osteomalacia (TIO) is cured by complete resection; thus, diagnosis is important, particularly on biopsy. Although PMT have a classic histologic appearance of bland spindled cells with conspicuous vascular network and characteristic smudgy basophilic matrix, there is a broad histologic spectrum and variant histologic patterns can make recognition difficult. Recent studies have demonstrated FN1-FGFR1 and FN1-FGF1 gene fusions in PMT; however, approximately 50% of cases are negative for these fusions. We sought to characterize 6 cases of PMT in-depth, compare fusion detection methods, and determine whether alternative fusions could be uncovered by targeted RNA sequencing. Of the 6 cases of PMT in our institutional archive, 3 were not given diagnoses of PMT at the time of initial pathologic examination. We characterized the immunoprofile (SMA, D2-40, CD56, S100 protein, desmin, SATB2, and ERG) and gene fusion status (FN1 and FGFR1 rearrangements by fluorescent in situ hybridization (FISH) and two targeted RNA sequencing approaches) in these cases. Tumors were consistently positive for SATB2 and negative for desmin, with 5/6 cases expressing ERG and CD56. One specimen was acid-decalcified and failed FISH and RNA sequencing. We found FN1 gene rearrangements by FISH in 2/5 cases, and a FN1-FGFR1 fusion by targeted RNA sequencing. No alternative gene fusions were identified by RNA sequencing. Our findings suggest that IHC and molecular analysis can aid in the diagnosis of PMT, guiding excision of the tumor and resolution of osteomalacia.

Lessons learnt from delayed diagnosis of FGF-23-producing tumour-induced osteomalacia and post-operative hungry bone syndrome

Tumour-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by a fibroblast growth-factor-23 (FGF-23)-secreting phosphaturic mesenchymal tumour (PMT) and is characterised by hypophosphataemic osteomalacia. We present a 36-year-old man initially presenting with diffuse bone and joint pain who was inappropriately treated for presumed ankylosing spondylitis for 2 years. Whole-body bone scan suggested metabolic bone disease, prompting referral to our endocrine institution. He was subsequently diagnosed with persistent hypophosphataemia, inappropriately high renal tubular phosphate excretion, 1,25-dihydroxyvitamin D₃ suppression, severe osteoporosis and severe osteomalacia. FGF-23 concentrations (140 ng/L) were raised 3-fold above the upper limit of normal. Initial Gallium-68 (⁶⁸Ga) DOTATATE positron emission tomography (PET)/CT scan missed an active lesion in the left fibular head as the field only included the mid-brain to the proximal femora. Histopathology results from tumour resection confirmed a PMT over-expressing FGF-23. Serum phosphate and FGF-23 normalised immediately post-operatively. He developed severe hypocalcaemia 3-weeks post-operatively (1.77 mmol/L) which normalised after 1 month of high-dose caltrate and calcitriol therapy. Osteomalacia, osteoporosis and associated symptoms resolved during medium-term follow-up with >100% improvement in his bone mineral density. This case report and discussion highlights the pitfalls contributing to delayed diagnosis of TIO and alerts clinicians to the potential complication of hungry bone syndrome post-tumour resection.

An intracranial mass causing tumor-induced osteomalacia (TIO): Rapid and complete resolution of severe osteoporosis after surgical resection

Tumor-induced osteomalacia (TIO) is a rare disease in which patients suffer from fractures and progressive disabling bone pain and muscle weakness. TIO is caused by the hypersecretion of Fibroblast Growth Factor 23 (FGF23) from rare neoplasms of mesenchymal origin. This case report describes a 29-year-old male with 2 years of low back/hip pain, gait changes, proximal muscle weakness, and multiple stress fractures. Bone densitometry was remarkable for severe osteoporosis, hypophosphatemia was seen on routine labs, and advanced labs demonstrated an "inappropriately normal" FGF23 level. A 68Ga-DOTATATE scan and MRI showed a 1.3 × 1.1 × 1.0 cm intracranial mass. The patient underwent tumor resection by Neurosurgery. Shortly after, laboratory levels normalized, and the patient's symptoms improved drastically. This case exemplifies the notion that TIO can be caused by FGF23 levels within normal limits, the role of 68-Ga DOTATATE imaging for establishing a diagnosis, and that these tumors can arise anywhere-even intracranially. We also review current surgical and nonsurgical treatment options, as well as emerging novel therapeutics.

SATB2 is frequently expressed in ossifying and non-ossifying peripheral oral fibroma of the gingival region but not in reactive fibromatous lesions from other intraoral sites

Ossifying and non-ossifying peripheral oral fibromas (POF) of the gingival and alveolar mucosa are localized, cellular, small fibrous nodular lesions likely resulting from diverse external/ internal physical and chemical irritation or injuries. A central nidus of metaplastic woven bone characterizes and defines the ossifying variant. The inherent tendency of these lesions to ossify remains elusive. We herein analyze SATB2 expression as osteoblastic transcription and differentiation factor in 28 gingival POFs (10 of them ossifying) and compare them to 28 fibrous lesions from different non-gingival intraoral sites. Strong to moderate diffuse nuclear SATB2 immunoreactivity was detected in all ossifying (10/10; 100%) and in 8/18 (44%) non-ossifying gingival POFs, but in only 1/28 (3%) non-gingival oral reactive nodular fibrous lesions. This study illustrates for the first-time consistent expression of the osteoblastic marker SATB2 in ossifying and most of non-ossifying POFs of the gingival area but lack of this marker in reactive fibrous lesions from other oral cavity sites. This finding is in line with the proposed origin of gingival POFs from periodontal ligaments and may explain the frequent ossification observed in them. It is mandatory to consider this finding when assessing biopsies from SATB2-positive oral cavity neoplasms to avoid misinterpretation.

[Molecular pathology in the diagnosis of bone tumors: current concepts]

The integrative evaluation of histology and corresponding imaging is essential for the classification of bone tumors. Until a few years ago, there were hardly any molecular markers that could be used for diagnostic purposes. However, exome- and genome-wide sequencing analyses have since uncovered a number of tumor-specific aberrations that can be very helpful in ambiguous cases. In addition to characteristic gene mutations (e.g. H3F3A and H3F3B in giant-cell tumors and chondroblastomas), the detection of fusion transcripts (e.g. structural rearrangements in the AP‑1 transcription factors FOS and FOSB in osteoid osteomas and osteoblastomas) plays an increasing role. The article gives an overview of the current state of knowledge of the most important alterations in bone tumors.

Surgical Treatment and Outcomes for Sinonasal and Skull Base Phosphaturic Mesenchymal Tumors

OBJECTIVE

To describe our clinical experience with surgical treatments for sinonasal phosphaturic mesenchymal tumors diagnosed at our institution.

STUDY DESIGN

Retrospective case series.

SETTING

Affiliated Sixth People's Hospital, Shanghai Jiao Tong University.

SUBJECTS AND METHODS

We retrospectively reviewed the medical records of 10 patients diagnosed with phosphaturic mesenchymal tumors associated with tumor-induced osteomalacia between December 2014 and October 2019.

RESULTS

There were 4 men and 6 women with a disease course of 1 to 19 years. All patients exhibited hypophosphatemia and tumor-induced osteomalacia. The tumor was located in the sinonasal region, frontal bone, and temporal bone in 8 patients, 1 patient, and 1 patient, respectively. Technetium-99m octreotide scintigraphy was used for tumor localization in 4 cases. Six patients underwent endoscopic resection; the remaining 4 underwent unilateral transorbital anterior and posterior ethmoid artery ligation + endoscopic resection, endoscopic resection + skull base repair, internal carotid artery stenting + transcatheter arterial embolization + temporal bone tumor excision + adipose tissue plugging, and endoscopic resection + transfrontal craniotomy (n = 1 each). Two patients had a history of incomplete endoscopic resection. All patients achieved clinical remission and normalized biochemical indices after surgery. Only 1 patient developed recurrence and died of a brain hernia.

CONCLUSIONS

A diagnosis of sinonasal phosphaturic mesenchymal tumors should be based on a combination of clinical, imaging, and pathological findings. Technetium-99m octreotide scintigraphy helps in locating the tumor. Complete surgical excision guarantees clinical remission, and preoperative transcatheter arterial embolization or feeding artery ligation may reduce intraoperative bleeding in cases of highly vascularized tumors.

Soft Tissue Special Issue: Giant Cell-Rich Lesions of the Head and Neck Region

Giant cell-rich lesions represent a heterogeneous group of tumors and non-neoplastic lesions, usually arising in bone, which harbor varying number of reactive osteoclastic-type multinucleate giant cells as a common feature. Among these entities, some are confined to the head and neck region (e.g., central giant cell granuloma and mimicking lesions, i.e., peripheral giant cell granuloma and cherubism) or show a relative predilection for this region (e.g., aneurysmal bone cyst and brown tumor of hyperparathyroidism), while others are rare but associated with distinct underlying disease (e.g., giant cell tumor of bone) or histology (e.g., tenosynovial giant cell tumor of the temporomandibular joint and phosphaturic mesenchymal tumor of the jaws) when occurring in the head and neck. Collectively, these lesions pose great challenge in the pathologic diagnosis, which often requires combinatory assessment from the clinical, histopathologic, and/or molecular aspects. This review provides a summary of pertinent clinical and pathologic features and an update of recent molecular and genetic findings of these entities. The considerations in differential diagnosis as well as the effects of the emerging therapeutic RANKL-antagonizing antibody denosumab will also be addressed.

Phosphaturic Mesenchymal Tumors from Head to Toe: Imaging Findings and Role of the Radiologist in Diagnosing Tumor-Induced Osteomalacia

BACKGROUND

This study aimed at evaluating the imaging findings of phosphaturic mesenchymal tumors and tumor-induced osteomalacia and assess the clinical and biochemical profiles of patients with tumor-induced osteomalacia.

MATERIALS AND METHODS

Imaging findings in six patients with tumor-induced osteomalacia and histopathologically proven phosphaturic mesenchymal tumors were evaluated. Clinical and biochemical profiles of these patients were also assessed.

RESULTS

Along with having a characteristic biochemical profile, patients with phosphaturic mesenchymal tumors also have certain imaging findings which can aid in the diagnosis such as increased uptake on DOTA PET-CT and homogeneous post-contrast enhancement on CT and MRI.

CONCLUSION

Patients with tumor-induced osteomalacia have characteristic symptoms, imaging and biochemical profiles. For radiologists, raising the suspicion of a phosphaturic mesenchymal tumor in patients with refractory hypophosphatemic osteomalacia as well as localizing the tumor on imaging is crucial, as complete excision of the tumor leads to resolution of the osteomalacia and the patient's clinical symptoms.

Tumor induced osteomalacia in head and neck region: single center experience and systematic review

Tumor-induced osteomalacia in the head and neck region remains a challenging diagnosis to manage. Literature pertaining to management and outcome details remains sparse. We describe two cohorts: cohort 1 included seven patients from a single center in Western India with tumors located in paranasal sinuses (n = 3), intracranial (n = 2) and maxilla (n = 2). The unique features from our series is the management of persistent disease with radiation therapy (n = 2) and peptide receptor radionuclide therapy (PRRT) (n = 1). Cohort two has 163 patients identified from 109 publications for systematic review. Paranasal sinuses, mandible, intracranial disease, maxilla and oral cavity, in descending order, are reportedly common tumor sites. Within this cohort, mean age was 46 ± 14 years at presentation with 44.1% having local symptoms. Duration of symptoms varied from 1 to 240 months. Pre-surgery mean serum phosphorus was 1.4 ± 0.4 mg/dL and median FGF-23 levels were 3.6 (IQR:1.8-6.8) times of normal upper limit of normal. Majority (97.5%) were managed primarily with surgical excision; however, primary radiotherapy (n = 2) and surgery combined with radiotherapy (n = 2) were also reported. Twenty patients had persistent disease while nine patients had recurrence, more commonly noted with intracranial and oral cavity tumors. Surgery was the most common second mode of treatment employed succeeded by radiotherapy. Four patients had metastatic disease. The most common histopathological diagnosis reported is PMT mixed connective tissue, while the newer terminology 'PMT mixed epithelial and connective tissue type' has been described in 15 patients.