FUS::CREM fusion is a distinct primary driver in rare neoplasms of the head and neck and other anatomic sites. Herein, we describe the clinicopathological, imaging, and molecular features of a malignant epithelioid mesenchymal neoplasm harboring FUS::CREM fusion, arising in the tongue of a 46-year-old male. Clinically, the patient presented with a left upper neck mass. Imaging revealed a 4.0 cm mass at the left base of tongue. Histologically, the tumor consisted of sheets of loosely cohesive, small round to ovoid cells with moderate cytoplasm, small nuclei with coarse chromatin, frequent nuclear pseudoinclusions, and dense peripheral lymphoplasmacytic and histiocytic infiltrates. Malignant features, including tumor necrosis, perineural invasion, and increased mitotic activity were observed; however, lymphovascular invasion was absent with no evidence metastatic disease in the examined lymph nodes. A comprehensive panel of immunohistochemical stains showed positivity for synaptophysin and ALK, with negative results for all other markers. RNA-based next-generation sequencing using anchored multiplex polymerase chain reaction (PCR) was performed and detected FUS::CREM fusion gene. The patient was treated by excision and postsurgical chemoradiation with no evidence of recurrence after four months. Additional cases supported by comprehensive clinical data collected over an extended period are necessary to precisely characterize epithelioid mesenchymal neoplasms harboring FUS::CREM fusion in the head and neck.

Ectomesenchymal chondromyxoid tumor (ECT) is a rare soft tissue tumor with peculiar histogenesis, exhibiting a predilection for the dorsum of the tongue. Molecular evidence suggests that it may originate from the migration of ectomesenchymal pluripotent cells from the neural crest to the tongue, where these cells may eventually proliferate and undergo myxoid and chondroid differentiation. This article illustrates a case of a 16-year-old female patient who presented with a nodule on the dorsum of her tongue, which had been present for four years. Surgical excision was performed, and histopathological analysis revealed a myxoid neoplasia composed of polygonal and spindle cells within a loose stroma containing chondroid areas. Tumor cells were positive for GFAP and S-100 proteins on immunohistochemical study, confirming the diagnosis of ECT. After a 5-year follow-up, the patient has shown no evidence of recurrence. Although rare, ECT can be diagnosed straightforwardly due to its distinctive clinical, histopathological, and immunohistochemical features. Clinicians and pathologists should become familiar with this tumor in order to avoid misdiagnosis.

METHODS: A healthy, 19-year-old woman was incidentally found to have a large, destructive tumor of T11 without neurologic symptoms. Biopsy demonstrated fibrocartilaginous mesenchymoma (FCM). The patient was treated with resection including subtotal corpectomy and T8-L1 fusion with use of cage and allograft strut construct. The patient remained without recurrence over 3 years of follow-up.
CONCLUSIONS: FCM arising from the spine is a rare tumor, of which this is the sixth report. FCM affects primarily young adults and is benign but locally aggressive, requiring complete excision to prevent recurrence.

Tumor-induced osteomalacia (TIO) is a disorder in which the clinical signs and symptoms of osteomalacia and the biochemical abnormalities of hypophosphatemia, phosphaturia, and low serum levels of 1,25(OH)2 Vitamin D3 are secondary to a neoplasm. A 33-year-old woman presented with musculoskeletal pain and proximal myopathy with a duration of 2.5 years which was treated with Vitamin D supplements. On the basis of the biochemical tests and histopathology, she was reevaluated and found to have TIO secondary to a phosphaturic mesenchymal tumor. The tumor was resected (limb salvage with endoprosthesis), and she had no pain or weakness at followup. The case reminds the readers to consider the possibility of TIO when evaluating patients with isolated hypophosphatemia, which may lead to long-term disability and prolonged morbidity if untreated. Early recognition and diagnosis of TIO is crucial since resection of the tumor usually reverses its manifestations.

Intimal sarcomas (IS) are rare, malignant, rapidly progressive mesenchymal tumors that typically occur in the tunica intima of larger vessels, and they rarely involve the heart. IS are frequently misdiagnosed during the initial clinical presentation. This case report describes an uncommonly located IS, highlighting specific findings obtained through multimodality imaging.

BACKGROUND: Phosphaturic Mesenchymal Tumors (PMTs) are rare mesenchymal neoplasms known for producing Tumor-induced Osteomalacia (TIO). TIO is an uncommon paraneoplastic syndrome characterized by radiographic evidence of inadequate bone mineralization and analytical abnormalites.
METHODS: We sought to present a case of TIO caused by skull base PMT with intracranial extension, manifesting with pain, progressive weakness, and multiple bone fractures. Furthermore, a systematic review was performed, following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines. A search was conducted in PubMed database with title/abstract keywords \"Phosphaturic mesenchymal tumor\" and \"Osteomalacia.\" Search results were reviewed looking for intracranial or skull base tumors.
RESULTS: Our systematic review included 29 reported cases of intracranial PMT. In the reviewed cases there was a significative female predominance with 22 cases (75,86%). Osteomalacia was presented in 25 cases (86,20%). Bone fractures were present in 10 cases (34,48%). The most common site of involvement was the anterior cranial fossa in 14 cases (48,27%). Surgery was performed in 27 cases (93,10%) with previous tumor embolization in 4 cases (13,79%). Total recovery of the presenting symptoms in the first year was achieved in 21 cases (72,41%). Recurrence of the disease was described in 6 cases (25%).
CONCLUSIONS: Skull base PMTs with intracranial extension are extremely rare tumors. Most patients are middle-aged adults with a PMT predominantly located in anterior cranial fossa. Surgery is the current treatment of choice with optimal outcome at 1-year follow-up, although recurrence could be present in almost 25% of the cases.

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

BACKGROUND Phosphaturic mesenchymal tumor (PMT) is an extremely rare mesenchymal neoplasm that is commonly seen in bone and soft tissue. It is associated with a paraneoplastic syndrome, oncogenic osteomalacia, due to tumor-induced urinary phosphate wasting. It is demonstrated to be predominantly mediated by fibroblast growth factor 23 (FGF23)/fibroblast growth factor receptor 1 (FGFR1) axis. Clinically, PMT usually presents as a solitary lesion in the bone. The diagnosis of PMT is challenging due to its non-specific clinical manifestation, radiologic findings, and morphological features. CASE REPORT We report the case of a 50-year-old man presenting with multiple lytic bone lesions and associated pathologic fracture of the right femur, clinically suspicious for multiple myeloma or other metastatic malignant process. Resection from the right femur showed a hypercellular lesion composed of oval-to-spindled cells infiltrating the native trabecular bone with admixed multinucleated giant cells. Immunohistochemical (IHC) staining and in situ hybridization (ISH) demonstrated the tumor cells were positive for SATB2, ERG, FGFR1, and FGF23 ISH. DNA and RNA next-generation sequencing showed marked increases in mRNA levels of FGF23 and FGFR1. The constellation of clinicoradiologic, histomorphologic, IHC, and molecular findings supported a diagnosis of primary benign PMT. CONCLUSIONS This case report discusses a patient with PMT presenting with multifocal lesions due to tumor-induced osteomalacia at initial presentation. We hope that this report will increase the awareness of clinician and pathologists of PMT as a differential diagnosis in patients presenting with multifocal lytic bone lesions. In turn, this will prevent misdiagnosis and overtreatment of a typically benign process.

BACKGROUND: Phosphaturic mesenchymal tumor (PMT) is a rare tumor that causes tumor-induced osteomalacia. Patients present with non-specific symptoms secondary to renal phosphate wasting and decreased bone mineralization. We sought to assess: (1) What are the common presenting features, laboratory and imaging findings, histologic findings of phosphaturic mesenchymal tumors? (2) What are the available treatment strategies for phosphaturic mesenchymal tumors and their long-term outcomes in terms of local recurrence and symptom control after treatment?
METHODS: We retrospectively identified patients with a histologic diagnosis of PMT located in the axial or appendicular skeleton, or surrounding soft tissues. A total of 10 patients were finally included in our study.
RESULTS: Median tumor size was 1.9 cm (range, 1.1 to 6.1) and median time from symptom onset to diagnosis was 3 years (range, 0.5 to 15 years). All patients but one presented with hypophosphatemia (median 1.9 mg/dL, range 1.2 to 3.2). Pre-operative FGF-23 was elevated in all cases (median 423.5 RU/mL, range 235 to 8950). Six patients underwent surgical resection, three were treated percutaneously (radiofrequency ablation or cryoablation), and one refused treatment. Only one patient developed local recurrence and no patients developed metastatic disease. At last follow-up, nine patients showed no evidence of disease and one was alive with disease.
CONCLUSIONS: Phosphaturic mesenchymal tumor is a rare tumor presenting with non-specific symptoms. Surgery is the standard treatment when negative margins can be achieved without significant morbidity. In patients with small tumors in surgically-inaccessible areas, radiofrequency ablation or cryoablation can be performed successfully.

UNASSIGNED: A 68 Ga-DOTATATE PET/CT scan was conducted to locate the causative tumor responsible for suspected tumor-induced osteomalacia in a 56-year-old woman. The PET/CT images showed a focus in the right occipital region. Subsequent MRI showed an extra-axial nodule in the right occipital region, mimicking a meningioma. Although rare, an intracranial phosphaturic mesenchymal tumor was still suspected because of the typical clinical settings. Finally, phosphaturic mesenchymal tumor was confirmed by the postoperative pathology.