Identification of a novelFN1-FGFR1genetic fusion as a frequent event in phosphaturic mesenchymal tumour

ALK oncoproteins in atypical inflammatory myofibroblastic tumours: novel RRBP1-ALK fusions in epithelioid inflammatory myofibroblastic sarcoma

ALK oncogenic activation mechanisms were characterized in four conventional spindle-cell inflammatory myofibroblastic tumours (IMT) and five atypical IMT, each of which had ALK genomic perturbations. Constitutively activated ALK oncoproteins were purified by ALK immunoprecipitation and electrophoresis, and were characterized by mass spectrometry. The four conventional IMT had TPM3/4-ALK fusions (two cases) or DCTN1-ALK fusions (two cases), whereas two atypical spindle-cell IMT had TFG-ALK and TPM3-ALK fusion in one case each, and three epithelioid inflammatory myofibroblastic sarcomas had RANBP2-ALK fusions in two cases, and a novel RRBP1-ALK fusion in one case. The epithelioid inflammatory myofibroblastic sarcoma with RRBP1-ALK fusion had cytoplasmic ALK expression with perinuclear accentuation, different from the nuclear membranous ALK localization in epithelioid inflammatory myofibroblastic sarcomas with RANBP2-ALK fusions. Evaluation of three additional uncharacterized epithelioid inflammatory myofibroblastic sarcomas with ALK cytoplasmic/perinuclear- accentuation expression demonstrated RRBP1-ALK fusion in two cases. These studies show that atypical spindle-cell IMT can utilize the same ALK fusion mechanisms described previously in conventional IMT, whereas in clinically aggressive epithelioid inflammatory myofibroblastic sarcoma we identify a novel recurrent ALK oncogenic mechanism, resulting from fusion with the RRBP1 gene. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Characterization of FN1-FGFR1 and novel FN1-FGF1 fusion genes in a large series of phosphaturic mesenchymal tumors

Phosphaturic mesenchymal tumors typically cause paraneoplastic osteomalacia, chiefly as a result of FGF23 secretion. In a prior study, we identified FN1-FGFR1 fusion in 9 of 15 phosphaturic mesenchymal tumors. In this study, a total of 66 phosphaturic mesenchymal tumors and 7 tumors resembling phosphaturic mesenchymal tumor but without known phosphaturia were studied. A novel FN1-FGF1 fusion gene was identified in two cases without FN1-FGFR1 fusion by RNA sequencing and cross-validated with direct sequencing and western blot. Fluorescence in situ hybridization analyses revealed FN1-FGFR1 fusion in 16 of 39 (41%) phosphaturic mesenchymal tumors and identified an additional case with FN1-FGF1 fusion. The two fusion genes were mutually exclusive. Combined with previous data, the overall prevalence of FN1-FGFR1 and FN1-FGF1 fusions was 42% (21/50) and 6% (3/50), respectively. FGFR1 immunohistochemistry was positive in 82% (45/55) of phosphaturic mesenchymal tumors regardless of fusion status. By contrast, 121 cases of potential morphologic mimics (belonging to 13 tumor types) rarely expressed FGFR1, the main exceptions being solitary fibrous tumors (positive in 40%), chondroblastomas (40%), and giant cell tumors of bone (38%), suggesting a possible role for FGFR1 immunohistochemistry in the diagnosis of phosphaturic mesenchymal tumor. With the exception of one case reported in our prior study, none of the remaining tumors resembling phosphaturic mesenchymal tumor had either fusion type or expressed significant FGFR1. Our findings provide insight into possible mechanisms underlying the pathogenesis of phosphaturic mesenchymal tumor and imply a central role of the FGF1-FGFR1 signaling pathway. The novel FN1-FGF1 protein is expected to be secreted and serves as a ligand that binds and activates FGFR1 to achieve an autocrine loop. Further study is required to determine the functions of these fusion proteins.

FN1-EGF gene fusions are recurrent in calcifying aponeurotic fibroma

Calcifying aponeurotic fibroma (CAF) is a soft tissue neoplasm with a predilection for the hands and feet in children and adolescents. Its molecular basis is unknown. We used chromosome banding analysis, fluorescence in situ hybridization (FISH), mRNA sequencing (RNA-seq), RT-PCR, and immunohistochemistry to characterize a series of CAFs. An insertion ins(2;4)(q35;q25q?) was identified in the index case. Fusion of the FN1 and EGF genes, mapping to the breakpoint regions on chromosomes 2 and 4, respectively, was detected by RNA-seq and confirmed by RT-PCR in the index case and two additional cases. FISH on five additional tumours identified FN1-EGF fusions in all cases. CAFs analysed by RT-PCR showed that FN1 exon 23, 27 or 42 was fused to EGF exon 17 or 19. High-level expression of the entire FN1 gene in CAF suggests that strong FN1 promoter activity drives inappropriate expression of the biologically active portion of EGF, which was detected immunohistochemically in 8/9 cases. The FN1-EGF fusion, which has not been observed in any other neoplasm, appears to be the main driver mutation in CAF. Although further functional studies are required to understand the exact pathogenesis of CAF, the composition of the chimera suggests an autocrine/paracrine mechanism of transformation. Copyright © 2015 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Refinements in Sarcoma Classification in the Current 2013 World Health Organization Classification of Tumours of Soft Tissue and Bone

The fourth edition of the World Health Organization (WHO) Classification of Tumours of Soft Tissue and Bone was published in February 2013. The 2013 WHO volume provides an updated classification scheme and reproducible diagnostic criteria, which are based on recent clinicopathologic studies and genetic and molecular data that facilitated refined definition of established tumor types, recognition of novel entities, and the development of novel diagnostic markers. This article reviews updates and changes in the classification of bone and soft tissue tumors from the 2002 volume.

The hypoxia-inducible factor-1α activates ectopic production of fibroblast growth factor 23 in tumor-induced osteomalacia

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome in which ectopic production of fibroblast growth factor 23 (FGF23) by non-malignant mesenchymal tumors causes phosphate wasting and bone fractures. Recent studies have implicated the hypoxia-inducible factor-1α (HIF-1α) in other phosphate wasting disorders caused by elevated FGF23, including X-linked hypophosphatemic rickets and autosomal dominant hypophosphatemia. Here we provide evidence that HIF-1α mediates aberrant FGF23 in TIO by transcriptionally activating its promoter. Immunohistochemical studies in phosphaturic mesenchymal tumors resected from patients with documented TIO showed that HIF-1α and FGF23 were co-localized in spindle-shaped cells adjacent to blood vessels. Cultured tumor tissue produced high levels of intact FGF23 and demonstrated increased expression of HIF-1α protein. Transfection of MC3T3-E1 and Saos-2 cells with a HIF-1α expression construct induced the activity of a FGF23 reporter construct. Prior treatment of tumor organ cultures with HIF-1α inhibitors decreased HIF-1α and FGF23 protein accumulation and inhibited HIF-1α-induced luciferase reporter activity in transfected cells. Chromatin immunoprecipitation assays confirmed binding to a HIF-1α consensus sequence within the proximal FGF23 promoter, which was eliminated by treatment with a HIF-1α inhibitor. These results show for the first time that HIF-1α is a direct transcriptional activator of FGF23 and suggest that upregulation of HIF-1α activity in TIO contributes to the aberrant FGF23 production in these patients.

Phosphaturic Mesenchymal Tumor: 2 New Oral Cases and Review of 53 Cases in the Head and Neck

Phosphaturic mesenchymal tumor (PMT) is a rare neoplasm that secretes fibroblast growth factor-23 (FGF-23) and causes oncogenic osteomalacia. It occurs in adults with equal gender distribution and the most common location is the lower extremities, followed by the head and neck. Besides osteomalacia, the clinical presentation includes bone pain and multiple bone fractures. Microscopic features consist of spindle cells, multinucleated giant cells, and calcifications embedded in a chondromyxoid matrix. Laboratory findings indicate normal calcium and parathyroid levels, hypophosphatemia, and increased levels of FGF-23 that usually revert to normal after surgical removal. Due to its rarity, the purpose of the study was to report 2 new oral cases of PMT and to review the literature in the head and neck. The first case occurred in the gingiva and had been present for 6 years. The second case was a recurrence of a previously diagnosed PMT in the right mandible that metastasized to the lung and soft tissue. The literature review included 53 cases in the head and neck. There was a predilection for extra-oral sites (76%) compared to intra-oral sites (24%) with paranasal sinuses considered the most common location (38%) followed by the mandible (15%). There were 9 recurrences that included 3 malignant cases indicating a potentially aggressive tumor. Due to the indeterminate biological behavior of PMT and its rarity, a comprehensive evaluation of medical, laboratory, radiographic, and histological findings are crucial for a definitive diagnosis and treatment.

Immunohistochemical and molecular detection of the expression of FGF23 in phosphaturic mesenchymal tumors including the non-phosphaturic variant

Background

Phosphaturic mesenchymal tumors (PMTs) are rare neoplasms that are often associated with tumor-induced osteomalacia (TIO) due to excessive serum levels of fibroblast growth factor 23 (FGF23). PMTs share overlapping histologic features with other types of tumors; thus, accurate pathological diagnosis may be challenging. We performed an immunohistochemical examination of FGF23 expression in PMTs and other types of tumors, together with pertinent molecular analyses.

Methods

Seven PMTs (5 with TIO and 2 without TIO) and 46 other types of bone and soft tissue tumors were retrieved, and immunohistochemistry was performed using a commercially available anti-FGF23 antibody. In addition, FGF23 mRNA expression was detected by reverse transcription-polymerase chain reaction (RT-PCR), using RNA extracted from formalin-fixed, paraffin-embedded tissues.

Results

Immunohistochemical analysis of FGF23 expression showed distinct, punctate staining in the cytoplasm in 5 PMTs with TIO, whereas FGF23 expression was negative in the 2 PMTs without TIO and the other 46 tumors. FGF23 mRNA expression was detected in all 4 PMTs examined, as well as in 1 chondromyxoid fibroma and 1 myxoid liposarcoma. The real-time RT-PCR data showed that the relative expression levels of the FGF23 mRNA tended to be higher in PMTs with TIO than in PMTs without TIO, or in the chondromyxoid fibroma specimen.

Conclusions

Our data suggested that the feasibility of immunohistochemical detection of FGF23 may depend on the level of secreted FGF23 from tumor cells. Thus, immunohistochemistry for FGF23 is an useful diagnostic adjunct for PMT, although its utility appears to be limited in cases without TIO.

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.

Phosphaturic Mesenchymal Tumor Involving the Head and Neck: A Report of Five Cases with FGFR1 Fluorescence In Situ Hybridization Analysis

Phosphaturic mesenchymal tumor (PMT) is a rare neoplasm; however, it is the most common cause of tumor-induced osteomalacia (TIO), a paraneoplastic syndrome characterized by renal phosphate wasting and hypophosphatemia. A subset of PMTs harbours an FGFR1 translocation although this alteration has not been demonstrated in PMT involving a head and neck site. We present a series of five PMTs involving the head and neck and demonstrate the diagnostic utility of fluorescence in situ hybridization (FISH) for detecting FGFR1 translocations. Patients' age and sex, tumor location, original diagnosis, the duration of symptoms, the presence of TIO, biochemical results, and medical management were reviewed. The median age at presentation was 45 (range, 24-58 years) and TIO was present in three cases. Four tumors involved soft tissue and one involved bone. Four out of the five tumors in our series were initially misdiagnosed. Three tumors were ultimately categorized as malignant PMT (two patients developed metastatic disease). FGFR1 translocation was present in two out of four cases and remained unknown in one case. In summary, we report on five cases of PMTs arising in the head and neck and confirm utility of FGFR1 FISH in the diagnosis of a subset of PMT.

Gene fusions in soft tissue tumors: Recurrent and overlapping pathogenetic themes

Gene fusions have been described in approximately one-third of soft tissue tumors (STT); of the 142 different fusions that have been reported, more than half are recurrent in the same histologic subtype. These gene fusions constitute pivotal driver mutations, and detailed studies of their cellular effects have provided important knowledge about pathogenetic mechanisms in STT. Furthermore, most fusions are strongly associated with a particular histotype, serving as ideal molecular diagnostic markers. In recent years, it has also become apparent that some chimeric proteins, directly or indirectly, constitute excellent treatment targets, making the detection of gene fusions in STT ever more important. Indeed, pharmacological treatment of STT displaying fusions that activate protein kinases, such as ALK and ROS1, or growth factors, such as PDGFB, is already in clinical use. However, the vast majority (52/78) of recurrent gene fusions create structurally altered and/or deregulated transcription factors, and a small but growing subset develops through rearranged chromatin regulators. The present review provides an overview of the spectrum of currently recognized gene fusions in STT, and, on the basis of the protein class involved, the mechanisms by which they exert their oncogenic effect are discussed.

From epistaxis to bone pain-report of two cases illustrating the clinicopathological spectrum of phosphaturic mesenchymal tumour with fibroblast growth factor receptor 1 immunohistochemical and cytogenetic analyses

AIMS

Phosphaturic mesenchymal tumour (PMT) is a rare, recently described neoplastic entity. It is characterized by distinct histological features, which often occur together with oncogenic osteomalacia. Recently, a novel FN1-FGFR1 gene fusion has been described in a subset of PMTs. The aim of this study is to characterise the clinicopathological features of two PMTs, with FGFR1 immunohistochemical and cytogenetic analyses.

METHODS AND RESULTS

We present two contrasting cases of PMT, one occurring in the sinonasal region, and the other occurring in bone (proximal femur). In the former, local effects, including epistaxis and anosmia, dominated the clinical presentation, whereas the latter case presented with refractory bone pain, muscle weakness, and occult osteomalacia, the cause of which was only identified after 2 years. Both tumours showed characteristic histological features of PMT, including a monomorphic proliferation of round to ovoid cells, osteoclast-like multinucleated giant cells, and areas of 'smudgy' basophilic calcifications. Chromogenic in-situ hybridization showed fibroblast growth factor FGF-23 expression by the sinonasal tumour. By using immunohistochemistry, we also demonstrated, for the first time, FGF receptor 1 (FGFR1) protein overexpression in this tumour, for which FN1-FGFR1 gene fusion was not detected by fluorescence in-situ hybridization.

CONCLUSIONS

Our findings indicate that up-regulation of FGFR1 in phosphaturic mesenchymal tumours can occur via mechanisms other than FN1-FGFR1 fusion, raising the possibility of FGFR1 overexpression being a potential common pathway with pathophysiological and therapeutic implications.

Soft tissue tumors of the sinonasal tract

Primary soft tissue tumors arising in the sinonasal tract are rare. While many mesenchymal neoplasms have been reported in the nasal cavity, sinuses, and nasopharynx, few are distinctive to this anatomic region. Some tumor types are relatively more common in this area, such as schwannoma and rhabdomyosarcoma. Nasopharyngeal angiofibroma and sinonasal hemangiopericytoma are unique entities of the sinonasal tract, as well as the recently characterized biphenotypic sinonasal sarcoma. This review discusses the clinical, morphologic, and immunohistochemical features and currently known molecular data of the more frequently encountered soft tissue tumors of the sinonasal tract.

The New Kids on the Block: Recently Characterized Soft Tissue Tumors

Soft tissue pathology is a rapidly changing subspecialty. New entities are described relatively often, and new molecular findings for soft tissue tumors are reported in the literature almost every month. This article summarizes the major features and diagnostic approach to several recently characterized entities: superficial CD34-positive fibroblastic tumor, fibrosarcoma-like lipomatous neoplasm, angiofibroma of soft tissue, low-grade sinonasal sarcoma with neural and myogenic features, malignant gastrointestinal neuroectodermal tumor, hemosiderotic fibrolipomatous tumor, and epithelioid inflammatory myofibroblastic sarcoma. Additionally, the article also provides a summary table of recent molecular findings in soft tissue tumors.

The PTH-Vitamin D-FGF23 axis

Fibroblast growth factor 23 (FGF23) has emerged as an important regulator of phosphate and vitamin D homeostasis. It is important to understand how FGF23 interacts with vitamin D and parathyroid hormone (PTH) in a FGF23-Vitamin D-PTH axis to regulate mineral homeostasis. In this review, we discuss the genomic structure, and transcriptional, translational, and posttranslational regulation of FGF23. We describe its interaction with PTH and vitamin D, disorders of altered FGF23 states, and emerging therapies for diseases of FGF23 based upon these findings. This discussion helps redefine the role of PTH and vitamin D in relation to a complex bone-kidney-parathyroid loop, and points to areas within this complicated field in need of further clarification and research.

Functions of Fibroblast Growth Factor Receptors in cancer defined by novel translocations and mutations

The four receptor tyrosine kinases (RTKs) within the family of Fibroblast Growth Factor Receptors (FGFRs) are critical for normal development but also play an enormous role in oncogenesis. Mutations and/or abnormal expression often lead to constitutive dimerization and kinase activation of FGFRs, and represent the primary mechanism for aberrant signaling. Sequencing of human tumors has revealed a plethora of somatic mutations in FGFRs that are frequently identical to germline mutations in developmental syndromes, and has also identified novel FGFR fusion proteins arising from chromosomal rearrangements that contribute to malignancy. This review details approximately 200 specific point mutations in FGFRs and 40 different fusion proteins created by translocations involving FGFRs that have been identified in human cancer. This review discusses the effects of these genetic alterations on downstream signaling cascades, and the challenge of drug resistance in cancer treatment with antagonists of FGFRs.