Endometrial stromal tumors: A clinico-histomorphological spectrum of endometrial stromal tumors with review of literature.

BACKGROUND: Endometrial stromal tumors (ESTs) are rare subset of mesenchymal uterine neoplasms. There are heterogeneous morphological, immunohistochemical, and genetic features. Approximately 50% of ESTs occur in perimenopausal women. In 2020, WHO sub-categorized ESTs into four groups: endometrial stromal nodule (ESN), low-grade endometrial stromal sarcoma (LGESS), high-grade endometrial stromal sarcoma (HGESS), and undifferentiated uterine sarcoma (UUS). OBJECTIVE: To review the morphological spectrum of endometrial stromal tumors. METHOD: This retrospective study reviewed the histomorphological features of 15 endometrial stromal tumors with respect to atypia, necrosis, mitosis, collagen bands, whorling around vessels, myometrial invasion, and inflammatory cells. Immunohistochemistry markers (CD10, SMA, and ER) along with special stains (Masson's trichrome, toluidine blue) were also studied. RESULTS: The age of the patients ranged from 32 to 60 years. Three patients were postmenopausal. The most common presenting symptom was vaginal bleeding. Five patients were operated with a clinical diagnosis of uterine fibroid. One patient presented with prolapse with no other complaint. All the 15 patients had total abdominal hysterectomy and salpingo-oophorectomy. One case showed necrosis, eight cases showed collagen bands, all the 15 cases showed whorling around vessels, one case showed vascular emboli, and seven cases showed inflammatory cells. In low-grade cases, one case showed focal atypia and one case showed focal coagulative necrosis indicating infarction. Thirteen cases were LGESS, and one case of ESN and HGESS. All cases were positive for ER and CD10. CONCLUSION: Endometrial stromal tumors demonstrate extensive permeation of the myometrium as irregular islands with frequent vascular invasion, whorling around vessels, collagen bands, and inflammatory cells. All these features should be observed thoroughly on microscopy by pathologists to clearly differentiate the low-grade and high-grade endometrial stromal tumors, and to understand the overlapping gray areas morphologically as it affects the prognosis of the patient.

Refractory Pneumothorax Due to Cystic Pulmonary Metastasis of a Lowgrade Endometrial Stromal Sarcoma: A Case Report.

Low-grade endometrial stromal sarcoma (LG-ESS) is a rare uterine neoplasm. Computed tomography (CT) revealed the presence of multiple small bilateral pulmonary nodules in a 58-year-old woman 1 year after surgery for LG-ESS; the clinical diagnosis was pulmonary metastasis. Hormone therapy with progesterone was initiated, after which most of the solid nodules disappeared and some transformed into cystic lesions. Seven years after hormone therapy, the patient experienced repeated pneumothorax. The cause of the pneumothorax was perforation of a metastatic focus within the wall of a small subpleural cyst that was not evident on CT images.

Identification of hub genes distinguishing subtypes in endometrial stromal sarcoma through comprehensive bioinformatics analysis.

Diagnosing low-grade and high-grade endometrial stromal sarcoma (LG-ESS and HG-ESS) is a challenge. This study aimed to identify biomarkers. 22 ESS cases were analyzed using Illumina microarrays. Differentially expressed genes (DEGs) were identified via Limma. DEGs were analyzed with String and Cytoscape. Core genes were enriched with GO and KEGG, their pan-cancer implications and immune aspects were studied. 413 DEGs were found by exome sequencing, 2174 by GSE85383 microarray. 36 common genes were identified by Venn analysis, and 10 core genes including RBFOX1, PCDH7, FAT1 were selected. Core gene GO enrichment included cell adhesion, T cell proliferation, and KEGG focused on related pathways. Expression was evaluated across 34 cancers, identifying immune DEGs IGF1 and AVPR1A. Identifying the DEGs not only helps improve our understanding of LG-ESS, HG-ESS but also promises to be potential biomarkers for differential diagnosis between LG-ESS and HG-ESS and new therapeutic targets.

[Diagnosis of uterine sarcomas and rare uterine mesenchymal tumours with malignant potential. Guidelines of the French Sarcoma Group and Rare Gynaecological Tumours]. / Diagnostic des sarcomes utérins et tumeurs mésenchymateuses utérines rares à potentiel de malignité. Référentiels du Groupe Sarcome Français et des Tumeurs Rares Gynécologiques.

The landscape of uterine sarcomas is becoming more complex with the description of new entities associated with recurrent driver molecular alterations. Uterine sarcomas, in analogy with soft tissue sarcomas, are distinguished into complex genomic and simple genomic sarcomas. Leiomyosarcomas and undifferentiated uterine sarcomas belong to complex genomic sarcomas group. Low-grade and high-grade endometrial stromal sarcomas, other rare tumors associated with fusion transcripts (such as NTRK, PDGFB, ALK, RET ROS1) and SMARCA4-deficient uterine sarcoma are considered simple genomic sarcomas. The most common uterine sarcoma are first leiomyosarcoma and secondly endometrial stromal sarcomas. Three different histological subtypes of leiomyosarcoma (fusiform, myxoid, epithelioid) are identified, myxoid and epithelioid leiomyosarcoma being more aggressive than fusiform leiomyosarcoma. The distinction between low-grade and high-grade endometrial stromal sarcoma is primarily morphological and immunohistochemical and the detection of fusion transcripts can help the diagnosis. Uterine PEComa is a rare tumor, which is distinguished into borderline and malignant, according to a risk assessment algorithm. Embryonal rhabdomyosarcoma of the uterine cervix is more common in children but can also occur in adult women. Embryonal rhabdomyosarcoma of the uterine cervix is almost always DICER1 mutated, unlike that of the vagina which is wild-type DICER1, and adenosarcoma which can be DICER1 mutated but with less frequency. Among the emerging entities, sarcomas associated with fusion transcripts involving the NTRK, ALK, PDGFB genes benefit from targeted therapy. The integration of molecular data with histology and clinical data allows better identification of uterine sarcomas in order to better treat them.

Highly malignant endometrial stromal sarcoma in a cat.

An 11-year-old female Persian cat underwent ovariohysterectomy due to dilation of the uterine cavity with irregular thickening of the wall. Macroscopically, the middle and distal regions of the left uterine horn were swollen and the uterine wall was irregularly thickened due to the development of multiple coalescent, variably sized nodules. Microscopically, the nodules had originated in the endometrium and were composed of round to polygonal neoplastic cells arranged in dense sheets or ill-defined fascicles. The neoplastic cells had locally invaded the myometrium and reached the subserosa, with lymphovascular invasion. Immunohistochemically, the neoplastic cell population was partially positive for CD10, an established marker of endometrial stromal sarcoma (ESS) in humans, with focal and diffuse nuclear immunopositivity for oestrogen and progesterone receptors and immunonegativity for desmin and α-smooth muscle actin. Based on these findings, the uterine tumour was diagnosed as ESS and was considered to correspond morphologically to high-grade ESS in humans.

An Unusual Endometrial Stromal Neoplasm With JAZF1-BCORL1 Rearrangement.

Endometrial stromal tumors represent the second most common category of uterine mesenchymal tumors. Several different histologic variants and underlying genetic alterations have been recognized, one such being a group associated with BCORL1 rearrangements. They are usually high-grade endometrial stromal sarcomas, often associated with prominent myxoid background and aggressive behavior. Here, we report an unusual endometrial stromal neoplasm with JAZF1-BCORL1 rearrangement and briefly review the literature. The neoplasm formed a well-circumscribed uterine mass in a 50-yr-old woman and had an unusual morphologic appearance that did not warrant a high-grade categorization. It was characterized by a predominant population of epithelioid cells with clear to focally eosinophilic cytoplasm growing in interanastomosing cords and trabeculae set in a hyalinized stroma as well as nested and fascicular growths imparting focal resemblance to a uterine tumor resembling ovarian sex-cord tumor, PEComa, and a smooth muscle neoplasm. A minor storiform growth of spindle cells reminiscent of the fibroblastic variant of low-grade endometrial stromal sarcoma was also noted but conventional areas of low-grade endometrial stromal neoplasm were not identified. This case expands the spectrum of morphologic features seen in endometrial stromal tumors, especially when associated with a BCORL1 fusion and highlights the utility of immunohistochemical and molecular techniques in the diagnosis of these tumors, not all of which are high grade.

High-grade endometrial stromal sarcoma displaying immunohistochemical expression of BCOR-A report of two cases of a novel tumor entity.

Several defining molecular alterations have recently been identified underlying high-grade endometrial stromal sarcomas, such as YWHAE: NUTM2A/B fusions, ZC3H7B: BCOR fusions, and BCOR internal tandem duplication (ITD). BCOR is a useful immunohistochemical marker for identifying these tumors. A 37-year-old lady was presented with a 10-cm-sized tumor in the pouch of Douglas, involving the vaginal vault, bilateral adnexa, and peritoneum. A 53-year-old lady with a prior hysterectomy was presented with a 12-cm-sized tumor in the vault with abdominal deposits. Histopathological examination of both tumors revealed atypical cells comprising oval to spindle-shaped nuclei, a variable amount of myxoid stroma, and mitotic figures exceeding 10/10 high power fields. Immunohistochemically, the former tumor was diffusely positive for CD10, and the second tumor displayed patchy staining. Both tumors were positive for BCOR. Estrogen receptor (ER) showed variable staining in both tumors. By fluorescence in-situ hybridization (FISH), both tumors lacked YWHAE gene rearrangement. Both tumors had an aggressive clinical course, including extensive involvement This constitutes the first report of BCOR-positive high-grade sarcomas involving the female genital tract from our subcontinent. BCOR is a useful immunostain for identifying these relatively aggressive tumors. The differential diagnoses and the prognosis of these ultra-rare tumors are discussed herewith.

ZC3H7B-BCOR Fusion High-grade Endometrial Stromal Sarcoma With Morphologic Features of Low-grade Endometrial Stromal Sarcoma. A Case Report and Review of Literature.

High-grade endometrial stromal sarcomas with ZC3H7B-BCOR fusion are rare. They are predominantly located in the endomyometrium, with morphologic features characterized as haphazardly arranged fascicles of spindle cells with mild to moderate atypia, abundant myxoid matrix, high mitotic index, and tongue-like/pushing patterns of myometrial invasion. Furthermore, conventional or variant low-grade endometrial stromal sarcomas are often not present. Clinically, they present at a higher stage and are associated with worse prognosis compared with low-grade endometrial stromal sarcoma. Given the limited number of reported cases, we describe the case of a ZC3H7B-BCOR fusion high-grade endometrial stromal sarcoma initially diagnosed on the hysterectomy specimen as low-grade endometrial stromal sarcoma based on an endometrial stromal tumor showing tongue-like myometrial and lymphovascular invasion, minimal cytologic atypia, low-mitotic activity (0-1/10 high-power field), round/spindle cell component and immunohistochemical stain results (positive for CD10, estrogen receptor, progesterone receptor, and focally positive for cyclin D1). At the time of pathologic diagnosis, she was Stage Ia and managed conservatively. Subsequent molecular analysis revealed a ZC3H7B (exon 10)- BCOR (BCL-6 corepressor) (exon 7) gene fusion. On follow-up, she showed no evidence of disease at 37 months from the time of diagnosis. This case report expands the morphologic spectrum of ZC3H7B-BCOR fusion high-grade ESS, which includes an intramural location, morphologic and immunophenotypic features similar to LG-ESS, as well as the presence of round and spindle cell components. This case also underscores the value of molecular analysis in the proper classification of ESS.

Clinical features of uterine sarcomas presenting mainly with uterine masses: a retrospective study.

BACKGROUND: Uterine sarcomas are uncommon mesenchymal tumors of the uterus. The clinical problem is that the features of uterine sarcomas can sometimes mimic uterine fibroids. This study aims to investigate the clinical characteristics of patients with uterine sarcomas who were preoperative presenting mainly with uterine masses. METHODS: A retrospective analysis of patients who underwent gynecological surgery for uterine sarcomas at the Obstetrics & Gynecology Hospital of Fudan University, between January 2016 and December 2021. RESULTS: Over the 5-year period, 277 patients were final diagnosed of uterine sarcomas. A total of 162 patients were preoperatively diagnosed as uterine fibroids for surgical treatment, the majority of whom were diagnosed of uterine leiomyosarcoma (uLMS) (49/162) and low-grade endometrial stromal sarcoma (LG-ESS) (100/162). Ninety people underwent total hysterectomy and bilateral salpingo-oophorectomy (TH + BSO), while 72 underwent myomectomy followed by supplemental TH + BSO. The group with direct hysterectomy had a higher average age than the group with prior myomectomy (47.20 ± 8.94 vs. 40.86 ± 5.88, p < 0.001). Among patients preoperatively diagnosed as uterine fibroids, patients with uLMS had a higher proportion of previous myomectomy (26.53% vs. 5.00%, p < 0.001), a larger uterine mass diameter on ultrasound (8.38 ± 3.39 cm vs. 6.41 ± 1.92 cm, p < 0.001), and richer hypervascularity (34.69% vs. 18%, p = 0.024) compared with LG-ESS. CONCLUSIONS: Analysis of our data showed that a large proportion of uterine sarcomas, especially uLMS and LG-ESS, present mainly with uterine masses. Ultrasound features including a large uterine mass diameter and rich hypervascularity, and with a history of myomectomy may alert clinicians in suspicion of uLMS when compared with LG-ESS.

Rare case of high-grade endometrial stromal sarcoma metastasising to inferior vena cava and right atrium.

Endometrial stromal sarcomas (ESSs) are a rare form of uterine malignancy representing <10% of all uterine sarcomas and <1% of all primary malignant tumours of the uterus. Invasion of the vascular system by low-grade ESS has been reported in the literature. Here we report the first case of a high-grade ESS invading the pelvic and gonadal vein and extending through the inferior vena cava to the right atrium, the diagnostic challenges and multidisciplinary management of the case.

Genomic and Transcriptomic Characterization Revealed the High Sensitivity of Targeted Therapy and Immunotherapy in a Subset of Endometrial Stromal Sarcoma.

PURPOSE: The unique chromosomal rearrangements of endometrial stromal sarcoma (ESS) make it possible to distinguish high-grade ESS (HGESS) and low-grade ESS (LGESS) from the molecular perspective. Analysis of ESS at the genomic and transcriptomic levels can help us achieve accurate diagnosis of ESS and provide potential therapy options for ESS patients. Materials and Methods: A total of 36 ESS patients who conducted DNA- and/or RNA-based next-generation sequencing were retrospectively enrolled in this study. The molecular characteristics of ESS at genomic and transcriptomic levels, including mutational spectrum, fusion profiles, gene expression and pathway enrichment analysis and features about immune microenvironment were comprehensively explored. RESULTS: TP53 and DNMT3A mutations were the most frequent mutations. The classical fusions frequently found in HGESS (ZC3H7B-BCOR and NUTM2B-YWHAE) and LGESS (JAZF1-SUZ12) were detected in our cohort. CCND1 was significantly up-regulated in HGESS, while the expression of GPER1 and PGR encoding estrogen receptor (ER) and progesterone receptor (PR) did not differ significantly between HGESS and LGESS. Actionable mutations enriched in homologous recombination repair, cell cycle, and phosphoinositide 3-kinase/AKT/mammalian target of rapamycin pathways were detected in 60% of HGESS patients. Genes with up-regulated expression in HGESS were significantly enriched in five immune-related pathways. Most HGESS patients (85.7%) had positive predictors of immunotherapy efficacy. Moreover, immune microenvironment analysis showed that HGESS had relatively high immune infiltration. The degree of immune infiltration in HGESS patients with ZC3H7B-BCOR fusion was relatively higher than that of those with NUTM2B-YWHAE fusion. CONCLUSION: This study investigated the molecular characteristics of ESS patients at the genomic and transcriptomic levels and revealed the potentially high sensitivity of targeted therapy and immunotherapy in a subset of HGESS with specific molecular features, providing a basis for guiding decision-making of treatment and the design of future clinical trials on precision therapy.

Spindle Cell Sarcoma of the Uterus Harboring MEIS1::NCOA1 Fusion Gene and Mimicking Endometrial Stromal Sarcoma.

MEIS1::NCOA1/2 sarcomas are a newly recognized group of exceedingly rare low-grade spindle cell sarcomas that often involve the genitourinary and gynecologic tracts. Due to its deceptively low-grade morphology and the non-specific immunoprofile, these neoplasms may pose a diagnostic challenge by histologically mimicking other entities such as endometrial stromal sarcoma, smooth muscle tumor, or uterine perivascular epithelioid cell tumor (PEComa). Histologically, MEIS1::NCOA1/2 sarcomas typically show spindle cell proliferation with hyperchromatic nuclei and a generalized cytologic uniformity, arranged in short fascicles and exhibiting alternating zones of hypo- and hypercellularity. Among the previously reported cases, molecular analysis revealed the MEIS1::NCOA2 fusion as the most commonly detected fusion gene, whereas the MEIS1::NCOA1 fusion gene has been reported in only a single case that involved kidney. Herein we report the first case of uterine sarcoma harboring the MEIS1::NCOA1 fusion gene that was initially misclassified as low-grade endometrial stromal sarcoma, demonstrating its clinicopathologic features, and highlighting the essential role of molecular pathology to arrive at the accurate diagnosis that may alter disease classification and inform therapy.

High-grade Endometrial Stromal Sarcoma: Morphologic and Clinical Features, the Role of Immunohistochemistry and Fluorescence in Situ Hybridization in Diagnosis.

Introduction. High-grade endometrial stromal sarcomas (HGESS) are rare malignant mesenchymal tumors of the uterus with aggressive poor clinical outcome, which frequently exhibit YWHAE::NUTM2 and ZC3H7B::BCOR fusions. In this study, we aimed to investigate HGESSs with YWHAE and BCOR translocations through our archive materials, and to identify morphological, immunohistochemical and molecular features of these tumors. We also assessed the diagnostic value of BCOR immunohistochemistry (IHC) in HGESSs, low-grade endometrial stromal sarcomas (LGESS) and uterine leiomyosarcomas. Methods. One hundred fifty-one uterine sarcomas diagnosed between 2000-2019 were reevaluated, and tumors of 39 patients with specific features were included in the study. Fluorescence in situ hybridization (FISH) studies using YWHAE and BCOR break-apart probes and BCOR IHC were performed. BCOR IHC was also performed in 20 leiomyosarcomas and 19 LGESSs. Results. In six HGESSs, translocations involving YWHAE or BCOR were detected. Five tumors showed high-grade morphology and revealed YWHAE translocation. One HGESS with myxoid morphology revealed BCOR translocation. In immunohistochemistry, three (3/4) YWHAE translocated HGESSs showed BCOR expression. However, the BCOR translocated HGESS was BCOR negative. The study showed that all LGESSs were immunohistochemically negative with BCOR. Although 15% (3/20) leiomyosarcomas reveal focal weak-moderate BCOR expression. Conclusion. BCOR IHC is a useful marker to distinguish LGESS from HGESS. A small percentage of uterine leiomyosarcomas reveal BCOR expression; however, it is not as diffuse and strong as in HGESSs. Strong and diffuse BCOR IHC expression is highly suggestive for HGESS. The diagnosis of HGESS should be supported by molecular studies such as FISH.

Highly cellular leiomyoma - A great histopathological masquerader of endometrial stromal sarcoma.

ABSTRACT: Leiomyoma is the most common benign uterine tumor, whereas endometrial stromal tumors are rare uterine tumors with limited clinical experience. The distinction between highly cellular leiomyoma and endometrial stromal sarcoma can pose a diagnostic challenge to the pathologists as both these tumors have considerable overlapping features on histology.

Fibroblastic variant of low-grade endometrial stromal sarcoma mimicking an inflammatory pseudotumor: a case report.

The World Health Organization currently divides endometrial stromal sarcomas into 4 different entities, based on their clinical and pathological features: endometrial stromal nodule, low-grade endometrial stromal sarcomas (LG-ESS), High-grade endometrial stromal sarcomas, and undifferentiated uterine sarcoma. The fibroblastic variant of LG-ESS is rare and is usually made of small tumoral cells of oval to fusiform shape, demonstrating low cytologic atypia and low mitotic activity, which can lead to confusion with a benign myofibroblastic proliferation. We hereby report a rare case of a fibroblastic variant of LG-ESS in a 37-year-old woman presenting abundant metrorrhagia, which was initially misdiagnosed as an inflammatory pseudotumor before proofreading in our laboratory, along with a review of a histological and immunohistochemical findings, aiming to help pathologists avoid this diagnosis pitfall.

Clinical characteristics and prognosis analysis of uterine sarcoma: a single-institution retrospective study.

BACKGROUND: Uterine sarcomas are rare and aggressive gynaecologic malignancies, characterized by a relatively high recurrence rate and poor prognosis. The aim of this study was to investigate the clinicopathological features and explore the prognostic factors of these malignancies. METHODS: This was a single-institution, retrospective study. We reviewed the medical records of 155 patients with pathologically confirmed uterine sarcomas including uterine leiomyosarcoma (ULMS), low-grade endometrial stromal sarcoma (LG-ESS), high-grade endometrial stromal sarcoma (HG-ESS), undifferentiated uterine sarcoma (UUS) and adenosarcoma (AS) between 2006 and 2022. A total of 112 patients who underwent surgery between January 2006 and April 2019 were included in the survival analysis. The current study recorded the clinicopathological, treatment and outcome data to determine clinical characteristics and survival. RESULTS: The most common histopathological type was ULMS (63/155, 40.64%), followed by LG-ESS (56/155, 36.13%) and HG-ESS (16/155, 10.32%). The mean age at diagnosis of all patients was 49.27±48.50 years and 32.90% (51/155) of patients were postmenopausal. Fifteen patients underwent fast-frozen sectioning, 63(54.78%) were diagnosed with malignancy, 29(25.22%) were highly suspected of malignancy that needed further clarification and 23(14.84%) were diagnosed with benign disease. A total of 124(80%) patients underwent total hysterectomy (TH) and salpingo-oophorectomy. Multivariate analyses showed that histological type and tumour size were independent prognostic factors both for overall survival (OS) (p<0.001 and P=0.017, respectively) and progression-free survival (PFS) (p<0.001 and P=0.018, respectively). Tumour stage was only significantly associated with PFS (P=0.002). Elevated preoperative NLR, PLR and postmenopausal status were significantly correlated with shorter PFS and OS in univariate analysis, but no statistically significant difference was found in multivariate analysis. CONCLUSIONS: In patients with uterine sarcoma, in comparison to LMS and LG-ESS, UUS and HG-ESS tend to present as more aggressive tumour with poorer outcomes. Furthermore, larger tumour (>7.5 cm) were an important predictor of shorter PFS and OS.

Uterine sarcomas and rare uterine mesenchymal tumors with malignant potential. Diagnostic guidelines of the French Sarcoma Group and the Rare Gynecological Tumors Group.

The landscape of uterine sarcomas is becoming increasingly complex with the description of new entities associated with recurrent molecular alterations. Uterine sarcomas, as well as soft tissue sarcomas, can be distinguished into complex genomic sarcomas and simple genomic sarcomas. Leiomyosarcoma and pleomorphic type undifferentiated uterine sarcoma belong to the first group. Low-grade and high-grade endometrial stromal sarcomas, NTRK, COL1A1::PDGFB, ALK, RET, ROS1 associated sarcomas, and SMARCA4 deficient uterine sarcoma belong to the second group. Leiomyosarcoma is the most common uterine sarcoma followed by endometrial stromal sarcomas. Three different histologic subtypes of leiomyosarcomas are recognized with distinct diagnostic criteria and different clinical outcomes, the myxoid and epithelioid leiomyosarcomas being even more aggressive than the fusiform type. The distinction between low-grade and high-grade endometrial stromal sarcoma is based first on morphology and immunohistochemistry. The detection of fusion transcripts helps in the diagnosis. Definitely recognized as a separate entity, uterine PEComa is a rare tumor whose diagnostic criteria are being recently defined. Uterine PEComa has a specific algorithm stratifying the tumors into uncertain malignant potential and malignant tumors. Embryonal rhabdomyosarcomas of the uterine cervix are not restricted to children but can also be observed in adult women and are almost always DICER1 mutated, unlike embryonal rhabdomyosarcoma of the vagina which are DICER1wild-type, and adenosarcoma which can be DICER1 mutated but with less frequency. As sarcomas associated with fusion transcripts involving the NTRK, ALK, COL1A1::PDGFB genes can benefit from targeted therapy, systematic detection are now relevant especially for patients with high risk of relapse or in recurrent setting. The integration of molecular data with dedicated expert pathology review for histology and clinical data allows better identification of uterine sarcomas in order to better treat them.

Highly Invasive and Metastatic High-grade Endometrial Stromal Sarcoma With BCOR Gene Alterations: A Case Report.

BACKGROUND: The coexistence of a uterine leiomyosarcoma and a high-grade endometrial stromal sarcoma (HGESS) is extremely rare, especially when one of the components causes metastasis. CASE REPORT: A 46-year-old female with aggravated abdominal pain for more than 4 months was diagnosed with uterine malignant mesenchymal tumor composed of predominantly a leiomyosarcoma (99%) and a minor component of HGESS with BCL6 corepressor (BCOR) gene alterations (1%), with ovarian and pelvic metastases. RESULTS: The volume of HGESS with BCOR gene alterations accounted for less than 1% of the tumor mass but caused ovarian and pelvic metastases. CONCLUSION: HGESS with BCOR gene alterations is extremely aggressive. We suggest that when both components of HGESS with BCOR gene alterations and uterine leiomyosarcoma are present in one patient, the HGESS with BCOR gene alterations needs to be highlighted in the pathological report, even if it accounts for less than 1% of the tumor volume.