Extraskeletal myxoid chondrosarcoma is a rare mesenchymal neoplasm of uncertain differentiation, characterized morphologically by abundant myxoid stroma, a multinodular growth pattern, and uniform cells arranged in strands, clusters, and reticular networks. It usually occurs in adults in the fifth decade, most often in the deep soft tissues of the proximal extremities. The molecular hallmark of this tumor, present in over 90% of cases, is the fusion of NR4A3 with EWSR1 at 22q12.2 or TAF15 at 17q12. Many other tumors with uniform tumor cells embedded in a myxoid matrix can mimic Extraskeletal myxoid chondrosarcoma, and the distinction can be difficult, often requiring immunohistochemistry and/or molecular testing. We herein report the case of an Extraskeletal myxoid chondrosarcoma that occurred in a 74-year-old woman who consulted for a slowly enlarging thigh mass, while highlighting the key morphologic, immunohistochemical, and molecular features of this rare type of soft tissue sarcoma, as well as a summary table gathering diagnostic features of relevance to the differential diagnosis.

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Malignant gastrointestinal neuroectodermal tumor (GNET), also referred to as clear cell sarcoma-like tumor of the GI tract is a rare mesenchymal tumor of the gastrointestinal tract. It has to be distinguished from various mimickers including gastrointestinal stromal tumor (GIST) due to its aggressive course and different natural history and therapeutic approach. Here we report a case of GNET arising in the small intestine with aberrant DOG1 expression posing a diagnostic challenge. In this context, the combination of clinical, histomorphological, immunohistochemical, and molecular features helped to establish a proper diagnosis.

BACKGROUND: Extraskeletal myxoid chondrosarcoma of the jugular foramen is a rare clinical entity, especially in the pediatric population. Thus, it can be confused with other pathologies.
METHODS: We report an extremely rare case of a 14-year-old female patient with jugular foramen myxoid chondrosarcoma that was completely removed through microsurgical resection.
CONCLUSIONS: The primary purpose of the treatment is gross total resection of the chondrosarcomas. However, adjuvant methods such as radiotherapy should additionally be applied in patients who have high-grade diseases or cannot undergo gross total resection because of anatomic localization.

GLI1-altered mesenchymal tumor is an emerging entity with distinctive clinicopathologic features. It shows a distinctive monomorphic round to epithelioid morphology, nested to trabecular pattern of growth, and S100+/SOX10-/SMA-immunophenotype. We report an example of this entity arising in the duodenum. A 31-year-old man presented with anemia for 1 year, a mass in the duodenal bulb was found for 9 days. Histopathologic examination revealed the tumor with distinct multilobulated architecture, a monomorphic appearance of round to epithelioid cells arranged in papillary structures, nests, cords, solid, reticular patterns, and hyalinized stroma surrounding a rich capillary network. The neoplastic cells had amphophilic to light eosinophilic or clear cytoplasm, uniform round nuclei with fine chromatin and inconspicuous nucleoli. Immunohistochemical analysis revealed strong positivity for vimentin, S100, CD56, CyclinD1, and negativity for SOX10, SMA, melan-A, HMB-45, synaptophysin, and a variety of other markers. Based on the morphology and immunophenotype, molecular studies were performed, which revealed the presence of an ACTB::GLI1 fusion transcript, confirming the diagnosis of GLI1-altered mesenchymal tumor.

Calcified chondroid neoplasms with FN1::FGFR1 or FGFR2 fusions constitute a recently described category of mesenchymal neoplasms mostly encountered in the extremities and temporomandibular joint. Herein, we report a case of FNI1-fused calcified chondroid neoplasm of the hand with a novel FGFR3 fusion partner. The tumor exhibited a multilobulated growth pattern composed of epithelioid cells embedded in abundant stroma with myxoid, chondroid, and fibrous areas and scattered osteoclast-like giant cells. RNA sequencing revealed an in-frame fusion between Exon 31 of FN1 and Exon 3 of FGFR3, which was subsequently confirmed by reverse transcription-polymerase chain reaction. Our findings expand on the spectrum of potential fusion partners in FN1-fused calcified chondroid neoplasms.

Extraskeletal myxoid chondrosarcoma (EMCS) is an undifferentiated mesenchymal malignancy; however, its immune microenvironment remains to be elucidated. The case of a 34-year-old woman who developed EMCS metastasizing to the pleura is presented here. The pleural EMCS showed hypervascularity, absent PD-L1 expression, and a lack of tumor mutational burden and pathogenic variants. Immunohistological examination of the pleural lesions showed predominant M2 macrophages and sparse CD8+ T cells. EMCS and the tumor stroma were positive for transforming growth factor-β1 (TGF-β1) and vascular endothelial growth factor (VEGF). In contrast, a small number of the stromal vessels were positive for hypoxia inducible factor-1α (HIF-1α). TGF-β1 and VEGF in the tumor stroma and low antigenicity of the tumor cells may help explain how EMCS induced the immunosuppressive microenvironment. These findings may encourage investigators to explore novel combined immunotherapy for EMCS, such as TGF-β1 and VEGF inhibitors, and specific therapy for enhancing tumor antigens.

Given the low incidence of musculoskeletal tumors during pregnancy, publications on the subject are scarce and treatment guidelines nonexistent. We present five cases of musculoskeletal tumors in pregnant women, three with metastasizing malignant neoplasms and two with aggressive giant cell tumors. The three patients diagnosed during their gestational period were operated before the end of pregnancy, adapting surgical techniques to minimize risk to mother and fetus. Adjuvant therapies were postponed until the end of gestation. All newborns were delivered at term vaginally, except for one where a cesarean section was required. After a mean follow-up of 69.96 months (±56.38), all patients were free of disease, except for the one diagnosed with an extraskeletal myxoid chondrosarcoma who died at 4 years from diagnosis. Surgery plays a key role in the treatment of musculoskeletal tumors diagnosed during pregnancy. These patients must be treated by multidisciplinary teams at sarcoma reference hospitals, involving the obstetrics team in the decision-making process, and adapting each step of the diagnosis and treatment to the gestational period. Key words: pregnancy, musculoskeletal tumors, sarcoma, cancer, oncological surgery.

Primary extraskeletal myxoid chondrosarcoma (pEMC) of the breast is rare and only a few cases have been reported to date. Herein, we report a case of primary EMC of the breast in a 45-year-old female. The patient presented with a left breast mass for 1 month. Mammogram revealed a fairly circumscribed mass with spicules of calcifications. The core biopsy and resection specimen showed a myxoid soft tissue neoplasm with histologic features of a myxoid chondrosarcoma. Necrosis, hemorrhage, and brisk mitotic activity were present. No malignant epithelial element was identified even after extensive sampling. The tumor cells exhibited immunoreactivity for vimentin, S100, neuron specific enolase, CD99, and synaptophysin, while the epithelial, myoepithelial, and mammary lineage-associated markers were negative. As up to 81% of EMC cases harbor t(9;22)(q22;q12), this results in a fusion of EWS RNA-binding protein 1 gene (EWSR1) at 22q12 to the nuclear receptor subfamily 4, group A, member 3 gene at 9q22. A rearrangement involving the EWSR1 locus was detected in our case. Whole body PET-CT did not reveal any other mass. A diagnosis of pEMC was rendered. The patient received six cycles of 5-Fluorouracil, Cyclophosphamide, and Adriamycin. The patient was in clinical and radiologic remission at the last follow-up (18 months post surgery). PET-CT and brain MRI were negative. In conclusion, surgical pathologists should include EMC in their differential while dealing with a myxoid soft tissue lesion of the breast, particularly in the core needle biopsies. An expeditious diagnosis of EMC of the breast would allow the surgeon to carry out conservative breast surgery instead of more radical approaches taken in cases of other primary malignant mammary neoplasms.

Mesenchymal tumors harboring GLI1 gene fusions are a rare new entity that typically occur in the head and neck region of young to middle aged adults, with a particular predilection for the tongue. We report herein a case of epithelioid mesenchymal tumor with PTCH1-GLI1 gene fusion of the right submental region in an 82-year-old male never smoker. Ultrasound-guided fine needle aspiration (FNA) with concomitant core needle biopsy was performed. Cytology smears revealed a hypercellular, monotonous aspirate comprised of epithelioid to plasmacytoid cells with round regular nuclei and moderate amounts of cytoplasm. There were admixed granulomata. The patient underwent surgical resection with limited neck dissection and subsequent pathologic examination with performed next generation sequencing confirmed the presence of epithelioid mesenchymal tumor with PTCH1-GLI1 gene fusion. To our knowledge, this is the first reported example of a mesenchymal tumor harboring GLI1 gene fusion initially evaluated by FNA.