Xanthogranulomatous epithelial tumor: report of 6 cases of a novel, potentially deceptive lesion with a predilection for young women

Keratin Positive Giant Cell Rich Tumor of the Pelvic Bone with a HMGA2::NCOR2 Fusion: A Case Report

Keratin positive giant cell rich tumor is a rare mesenchymal tumor first described in 2020. It can occur in both soft tissue and bone and predominantly affects young women. The tumor's biological behavior remains uncertain despite its low-grade classification. Characterized by keratin expression and a HMGA2::NCOR2 gene fusion, keratin positive giant cell rich tumors resemble conventional giant cell tumors but lacks H3-3A gene mutations. This article presents a 31-year-old woman with a keratin positive giant cell rich tumor in the pelvic bone, detailing her clinical presentation, diagnostic process, treatment, and postoperative recovery. Histological examination revealed numerous osteoclast-like giant cells within a mononuclear stroma, with RNA sequencing confirming the HMGA2::NCOR2 fusion. The patient's management included surgical resection, with no recurrence at six months follow-up. The discussion emphasizes the need for further research to understand keratin positive giant cell rich tumors pathogenesis and explore potential targeted therapies.

Xanthogranulomatous epithelial tumors/keratin-positive giant cell-rich tumors involving the head and neck: report of seven cases and review of the literature

Xanthogranulomatous epithelial tumor (XGET) and HMGA2::NCOR2 fusion keratin-positive giant cell-rich tumor (KPGCT) are recently described morphologically overlapping rare neoplastic entities characterized by HMGA2::NCOR2 fusions, low-grade biological behavior, and a strong predilection for young females. To date, 47 cases have been reported with only four occurring in head and neck anatomic locations. In this study, we describe the clinicopathologic, immunohistochemical, and molecular findings of seven XGET/KPGCTs occurring in the head and neck region. The patients were six females and one male, aged 3.5-59 years old (median, 25 years). The tumors involved the ear, vocal cord, skull, neck soft tissue, and sinonasal cavity. Tumor sizes ranged from 1.5 to 6.7 cm. Histologically, the tumors were characterized by xanthogranulomatous histiocytes, osteoclast-like giant cells, and keratin-positive epithelioid cells. The XGET/KPGCTs involving the ear was remarkable for more cytologic atypia than previously described. Four cases had the HMGA2::NCOR2 fusion identified by NGS and three had HMGA2 gene locus alterations by FISH. Follow-up information was available for 3 of 7 patients (range 6-46 months). The patient with a vocal cord XGET/KPGCTs developed a local recurrence treated with excision. This study illustrates that XGET/KPGCTs involves the head and neck region as well, where it may be unexpected and hence under-recognized, and expands the anatomic locations of involvement to include unreported sites (ear, vocal cord, and sinonasal tract).

Keratin-Positive Giant Cell-Rich Tumor: A Review and Update

Keratin-positive giant cell-rich tumor (KPGCT) is an extremely rare and recently described mesenchymal neoplasm that occurs in both soft tissue and bone, frequently found in young women. It has locally recurrent potential if incompletely excised but low risk for metastasis. KPGCT is histologically similar to conventional giant cell tumors of soft tissue but shows the presence of keratin-positive mononuclear cells. Interestingly, KPGCT also shares some morphological features with xanthogranulomatous epithelial tumors. These two tumors have recently been shown to harbor an HMGA2-NCOR2 fusion, arguing in favor of a single entity. Surgery is the treatment of choice for localized KPGCT. Therapeutic options for advanced or metastatic disease are unknown. This review provides an overview of the current knowledge on the clinical presentation, pathogenesis, histopathology, and treatment of KPGCT. In addition, we will discuss the differential diagnosis of this emerging entity.

Histones and their practical application in bone tumors: Do I always need them?

Historically, the diagnosis of giant cell-rich neoplasms arising in bone has been challenging owing to overlapping clinical and radiographic findings resulting in the difficult separation of several neoplasms, particularly when biopsy material is limited. However, with the discovery of the driver histone mutations in giant cell tumor of bone (GCTB) and chondroblastoma, as well as USP6 rearrangements in aneurysmal bone cyst, pathologists now have objective ancillary tools to aid in the separation of several histologically similar giant cell-rich neoplasms. Furthermore, the recognition of histone mutations has allowed pathologists to revisit several entities, such as "malignant chondroblastoma," and furthered our understanding of phenomena such as "aneurysmal bone cyst-like change," formerly recognized as "secondary aneurysmal bone cyst." Herein, the evolution of testing for histone mutations in bone tumors is considered; the sensitivity and specificity of the histone antibodies is reviewed; and a practical guide for the use of these ancillary tests is offered.

Keratin-Positive Giant Cell-Rich Tumor of Bone Harboring an HMGA2::NCOR2 Fusion: Two Cases, Including a Patient With Metastatic Disease, and Review of the Literature

Giant cell-rich lesions of bone represent a heterogeneous group of entities which classically include giant cell tumor of bone, aneurysmal bone cyst, nonossifying fibroma, and Brown tumor of hyperparathyroidism. A recently described subset of giant cell-rich tumors involving bone and soft tissue has been characterized by recurrent HMGA2::NCOR2 fusions and keratin expression. The overlapping clinical, radiographic, and morphological features of these giant cell-rich lesions provide a unique diagnostic challenge, particularly on biopsy. We present 2 additional cases of keratin-positive giant cell-rich tumor of bone with HMGA2::NCOR2 fusions, including 1 patient who developed metastatic disease.

Xanthogranulomatous Epithelial Tumors and Keratin-Positive Giant Cell Rich Tumors of Soft Tissue and Bone: Two Sides of the Same Coin

Xanthogranulomatous epithelial tumor is a recently described soft tissue tumor characterized by subcutaneous location, partial encapsulation, a xanthogranulomatous inflammatory cell infiltrate, and keratin-positive mononuclear cells. It shares some morphologic features with keratin-positive, giant cell-rich soft tissue tumors. Both have recently been shown to harbor HMGA2::NCOR2 fusions. The relationship between these tumors and their differential diagnosis with other osteoclast-containing soft tissue tumors is discussed.

CSF1 expression in xanthogranulomatous epithelial tumor/keratin-positive giant cell-rich tumor

"Xanthogranulomatous epithelial tumor" (XGET) and "keratin-positive giant cell-rich soft tissue tumor" (KPGCT), two recently described mesenchymal neoplasms, likely represent different aspects of a single entity. Both tumors are composed of only a small minority of tumor cells surrounded by large numbers of non-neoplastic inflammatory cells and histiocytes, suggesting production of a paracrine factor with resulting "landscape effect," as seen in tenosynovial giant cell tumor. Recent evidence suggests that the paracrine factor in XGET/KPGCT may be CSF1, as in tenosynovial giant cell tumor. We hypothesized that CSF1 is overexpressed in XGET/KPGCT. To test our hypothesis, we performed quantitative real time PCR (qPCR) for CSF1 expression and CSF1 RNAscope chromogenic in situ hybridization (CISH) on 6 cases of XGET/KPGCT. All cases were positive with CSF1 CISH and showed increased expression of CSF1 by qPCR. Our findings provide additional evidence that the CSF1/CSF1R pathway is involved in the pathogenesis of XGET/KPGCT. These findings suggest a possible role for CSF1R inhibition in the treatment of unresectable or metastatic XGET/KPGCT.

Xanthogranulomatous epithelial tumor: a novel entity of uncertain biologic potential

Xanthogranulomatous epithelial tumor (XGET) is an extremely rare and recently described mesenchymal neoplasm characterized by a distinctive histological appearance and clinical presentation. This case report describes a unique case of XGET in a 66-year-old female patient who presented with a 5 cm mass in the dorsal distal left thigh. The clinical, radiological, and pathological findings, as well as the management and follow-up, are discussed.

[Changes in the WHO classification (2020) of soft tissue tumors]

The article provides an overview of the main changes in the current (2020) WHO classification of soft tissue tumors, as well as selected updates that have occurred since the release of the classification.

Xanthogranulomatous epithelial tumors and keratin-positive giant cell-rich soft tissue tumors: two aspects of a single entity with frequent HMGA2-NCOR2 fusions

Xanthogranulomatous epithelial tumor (XGET) and keratin-positive giant cell-rich soft tissue tumor with HMGA2-NCOR2 fusion (KPGCT) are two recently described neoplasms with both distinct and overlapping clinical and histopathologic features. We hypothesized that XGET and KPGCT may be related and represent a histologic spectrum of a single entity. To test this, we sought to characterize the clinical, radiographic, immunohistochemical, ultrastructural and molecular features of additional tumors with features of XGET and/or KPGCT, which we refer to descriptively as keratin-positive xanthogranulomatous/giant cell-rich tumors (KPXG/GCT). The archives were searched for potential cases of KPXG/GCT. Clinical and imaging features were noted. Slides were assessed for histologic and immunohistochemical findings. Ultrastructural and next generation RNA sequencing-based analysis were also performed. Nine cases were identified arising in seven women and two men [median age of 33 years (range: 12-87)]. Median tumor size was 4 cm (range: 2.4-14.0 cm) and tumors presented in the thigh (2), buttock (1), forearm (2), groin (1), cranial fossa (1), ilium (1), and tibia (1). Morphologically, tumors were most frequently characterized by a fibrous capsule, with associated lymphoid reaction, enclosing a polymorphous proliferation of histiocytes, giant cells (Touton and osteoclast-types), mixed inflammatory infiltrate, hemorrhage and hemosiderin deposition, which imparted a variably xanthogranulomatous to giant cell tumor-like appearance. One case clearly showed mononuclear cells with eosinophilic cytoplasm characteristic of XGET. All cases expressed keratin and 7 of 9 were found to harbor HMGA2-NCOR2 fusions including cases with xanthogranulomatous appearance. One patient developed local recurrence and multifocal pulmonary lesions, which were radiographically suspicious for metastases. Shared clinical, histologic and immunohistochemical features, and the shared presence of HMGA2-NCOR2 fusions supports interpretation of KPXG/GCT as a single entity which includes XGET and KPGCT. Given limited clinical follow-up to date and rare cases with apparently aggressive findings, we provisionally regard these tumors as having uncertain biologic potential.

Xanthogranulomatous Cholecystitis Masquerading as Gallbladder Carcinoma on 68 Ga-FAPI-04 PET

ABSTRACT

68 Ga-FAPI-04 has great potential for the detection and staging evaluation of a variety of tumors. We report a case of suspected gallbladder carcinoma that was enrolled in a prospective study of 68 Ga-FAPI-04 imaging at our institution. This case was later histopathologically confirmed as xanthogranulomatous cholecystitis. This demonstrates that xanthogranulomatous cholecystitis might be disguised as gallbladder carcinoma in 68 Ga-FAPI-04 imaging. Thus, we suggest that nuclear clinicians evaluating 68 Ga-FAPI-04 imaging should be aware of this possibility.

Xanthogranulomatous Breast Mass: An Unusual Presentation

Xanthogranulomatous inflammatory reactions are benign inflammatory processes characterized by aggregating lipid-laden foamy macrophages. Although cases have been reported in different organ systems, these rare reactions predominantly occur in the kidney and gallbladder. We present a 92-year-old female who noticed a palpable, tender mass in the lower inner quadrant of her right breast with no skin changes. She was referred to surgery by her primary care physician on suspicion of malignancy and further evaluation. Ultrasound-guided biopsy, ordered by the primary care provider, revealed a suspicious high-grade malignant neoplasm of uncertain origin. Pathological findings include the presence of an unusual population of malignant epithelioid cells with a striking xanthogranulomatous reaction, along with numerous Touton-like histiocytes. These findings are comparable in morphology to a recently reported xanthogranulomatous epithelial tumor. Given the lack of history of breast carcinoma in this patient as well as the lack of immunohistochemical studies suggesting breast carcinoma, treatment involved continuing standard of care for an unusual high-grade sarcoma via lumpectomy. A positron emission tomography (PET) scan was ordered to ensure there was no spread or alternate origins of the cancer tissue. This case report brings to light the findings of a probable xanthogranulomatous tumor in breast tissue, an exceptionally rare phenomenon in breast cancer, especially in the elderly population. Due to the rarity of xanthogranulomatous tumors in the breast, prognosis and standardized treatment have yet to be established. 

Recurrent novel HMGA2-NCOR2 fusions characterize a subset of keratin-positive giant cell-rich soft tissue tumors

Giant cell tumors of soft tissue (GCT-ST) are rare low-grade neoplasms that were at one time thought to represent the soft tissue counterparts of GCT of bone (GCT-B) but are now known to lack the H3F3 mutations characteristic of osseous GCT. We present six distinctive giant cell-rich soft tissue neoplasms that expressed keratins and carried a recurrent HMGA2-NCOR2 gene fusion. Patients were five females and one male aged 14-60 years (median, 29). All presented with superficial (subcutaneous) masses that were removed by conservative marginal (3) or wide (2) local excision. The tumors originated in the upper extremity (2), lower extremity (2), head/neck (1), and trunk (1). Five patients with follow-up (median, 21 months; range, 14-168) remained disease-free. Grossly, all tumors were well-demarcated but not encapsulated with variable lobulation. Histologically, they were composed of bland plump epithelioid or ovoid to spindled mononuclear cells admixed with evenly distributed multinucleated osteoclast-type giant cells. Foci of stromal hemorrhage and hemosiderin were seen in all cases. The mitotic activity ranged from 2 to 14/10 high power fields (median: 10). Foci of necrosis and vascular invasion were seen in one case each. The mononuclear cells were immunoreactive with the AE1/AE3 keratin cocktail and less frequently/less diffusely for K7 and K19 but lacked expression of other lineage-associated markers. RNA-based next-generation sequencing revealed an HMGA2-NCOR2 fusion in all tumors. None of the keratin-negative conventional GCT-ST showed the HMGA2-NCOR2 fusion (0/7). Metaplastic bone (4/9) and SATB2 expression (3/4) were frequent in keratin-negative conventional GCT-ST but were lacking in keratin-positive HMGA2-NCOR2 fusion-positive tumors. The distinctive immunophenotype and genotype of these tumors strongly suggest that they represent a discrete entity, differing from conventional GCT-ST and other osteoclast-rich morphologic mimics. Their natural history appears favorable, although a study of additional cases and longer follow-up are warranted.

Xanthogranulomatous epithelial tumor: report of 6 cases of a novel, potentially deceptive lesion with a predilection for young women

Epithelial marker expression and/or epithelial differentiation, as well as "anomalous" expression of keratins, are features of some soft tissue tumors. Recently, we have encountered an unusual mesenchymal tumor composed of bland, distinctly eosinophilic, keratin-positive epithelial cells, which were almost entirely obscured by xanthogranulomatous inflammation. Six cases were identified (5 F, 1 M; 16-62 years (median 21 years)) arising in soft tissue (n = 4) and bone (n = 2) and ranging in size from 2 to 7 cm. The tumors were generally circumscribed, with a fibrous capsule containing lymphoid aggregates, and consisted in large part of a sheet-like proliferation of foamy histiocytes, Touton-type and osteoclast-type giant cells, and chronic inflammatory cells. Closer inspection, however, disclosed a distinct population of uniform, cytologically bland mononuclear cells with brightly eosinophilic cytoplasm arranged singly and in small nests and cords. Overt squamous and/or glandular differentiation was absent. By immunohistochemistry, these cells were diffusely positive with the OSCAR and AE1/AE3 keratin antibodies, and focally positive for high-molecular weight keratins; endothelial and myoid markers were negative and SMARCB1 was retained. RNA-seq identified a PLEKHM1 variant of undetermined significance in one case, likely related to this patient's underlying osteopetrosis. Follow-up to date has been benign. In summary, we have identified a novel tumor of soft tissue and bone with a predilection for young females, provisionally termed "xanthogranulomatous epithelial tumor". These unusual lesions do not appear to arise from adnexa, or represent known keratin-positive soft tissue tumors, and the origin of their constituent epithelial cells is obscure. The natural history of this distinctive lesion appears indolent, although study of additional cases and longer term follow-up are needed.