Phosphaturic mesenchymal tumor with chondromyxoid fibroma-like feature: an unusual morphological appearance

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.

CT and MR imaging features in phosphaturic mesenchymal tumor-mixed connective tissue: A case report

Phosphaturic mesenchymal tumor-mixed connective tissue (PMT-MCT) is rare and usually benign and slow-growing. The majority of these tumors is associated with sporadic tumor-induced osteomalacia (TIO) or rickets, affect middle-aged individuals and are located in the extremities. Previous imaging studies often focused on seeking the causative tumors of TIO, not on the radiological features of these tumors, especially magnetic resonance imaging (MRI) features. PMT-MCT remains a largely misdiagnosed, ignored or unknown entity by most radiologists and clinicians. In the present case report, a review of the known literature of PMT-MCT was conducted and the CT and MRI findings from three patient cases were described for diagnosing the small subcutaneous tumor. Typical MRI appearances of PMT-MCT were isointense relative to the muscles on T1-weighted imaging, and markedly hyperintense on T2-weighted imaging containing variably flow voids, with markedly heterogeneous/homogenous enhancement on post contrast T1-weighted fat-suppression imaging. Short time inversion recovery was demonstrated to be the optimal sequence in localizing the tumor.

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

Phosphaturic mesenchymal tumor (PMT) is a rare neoplasm of uncertain histogenesis that has been linked to tumor-induced osteomalacia (TIO) since 1959. The neoplastic cells produce increased amount of FGF23 which results in TIO via uncontrolled renal loss of phosphate (phosphaturia), and consequently diminished bone mineralization. To date, ∼300 cases have been reported. Although there is increasing evidence that PMT can be diagnosed by reproducible histopathologic features, firm diagnosis has been often restricted to cases associated with TIO and, hence, diagnosis of "nonphosphaturic variants" remained challenging. Recently, FGFR1/FN1 gene fusions were detected in roughly half of cases. We herein reviewed the clinicopathologic features of 22 PMTs (15 cases not published before), stained them with an extended immunohistochemical marker panel and examined them by fluorescence in situ hybridization for FGFR1 gene fusions. Patients were 12 males and 9 females (one of unknown sex) aged 33 to 83 years (median: 52 y). Lesions affected the soft tissues (n=11), bones (n=6), sinonasal tract (n=4), and unspecified site (n=1). Most lesions originated in the extremities (9 in the lower and 4 in the upper extremities). Acral sites were involved in 10 patients (6 foot/heel, 3 fingers/hands, and 1 in unspecified digit). Phosphaturia and TIO were recorded in 10/11 and 9/14 patients with detailed clinical data, respectively. Limited follow-up (5 mo to 14 y; median: 16 mo) was available for 14 patients. Local recurrence was noted in one patient and metastasis in another patient. Histologically, 11 tumors were purely of conventional mixed connective tissue type, 3 were chondromyxoid fibroma-like, 2 were hemangio-/glomangiopericytoma-like with giant cells, and 1 case each angiomyolipoma-like and reparative giant cell granuloma-like. Four tumors contained admixture of patterns (predominantly cellular with variable conventional component). Immunohistochemistry showed consistent expression of CD56 (11/11; 100%), ERG (19/21; 90%), SATB2 (19/21; 90%), and somatostatin receptor 2A (15/19; 79%), while other markers tested negative: DOG1 (0/17), beta-catenin (0/14), S100 protein (0/14), and STAT6 (0/7). FGFR1 fluorescence in situ hybridization was positive in 8/17 (47%) evaluable cases. These results add to the phenotypic delineation of PMT reporting for the first time consistent expression of SATB2 and excluding any phenotypic overlap with solitary fibrous tumor or sinonasal glomangiopericytoma. The unifying immunophenotype of the neoplastic cells irrespective of the histologic pattern suggests a specific disease entity with diverse morphotypes/variants rather than different neoplasms unified by TIO.

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.

Malignant phosphaturic mesenchymal tumor of the pelvis: A report of two cases

Tumor-induced osteomalacia (TIO) is a rare acquired form of hypophosphatemia commonly associated with phosphaturic mesenchymal tumors (PMTs) located in the bone or soft tissue. Resection of the tumor can cure osteomalacia. Fibroblast growth factor 23 has been identified as a major pathophysiological factor responsible for phosphaturia. The majority of PMTs are benign, and malignant PMTs are uncommon. Even in rare cases, the malignant transformation of PMTs is extremely uncommon. The current study presents two cases in which the patients succumbed to malignant PMTs that developed in the pelvis. The first patient was a 35-year-old female with a malignant PMT occurring as a synchronous double cancer associated with papillary thyroid carcinoma. Diagnosis was difficult, as the multiple uptake on positron emission tomography with 18F-fluorodeoxyglucose presented as pseudofractures mimicking the metastases of thyroid carcinoma. The patient succumbed to rapidly progressive lung metastases. The second patient presented with a pelvic tumor that had developed over 26 years. The patient was diagnosed with a benign PMT by open biopsy and a complete resection was performed. However, two years later, the tumor recurred and lung metastases were observed. The patient ultimately succumbed to respiratory failure due to relapsing lung metastases and disseminated intravascular coagulation. These two cases demonstrate the potential lethality of malignant PMTs and the malignant transformation of benign PMTs. Therefore, TIO patients must be followed up even if diagnosed with a benign tumor. Although TIO is an extremely rare disease, the possibility of malignant PMTs must be recognized.