BCOR Internal Tandem Duplication Associated Uterine Sarcoma: Expanding the Clinicopathologic Spectrum

BCOR abnormalities in endometrial stromal sarcoma

Endometrial stromal tumors (ESTs) are uncommon mesenchymal tumors of the reproductive system associated with heterogeneous histomolecular features. According to the World Health Organization (WHO), ESTs are classified into benign endometrial stromal nodules (BESN) and endometrial stromal sarcomas (ESSs), which are further divided into low-grade and high-grade subtypes. High-grade ESS is frequently associated with YWHAE-NUTM2 gene fusions, while a newly recognized subtype with BCOR rearrangements, including fusions, alterations, and internal tandem duplications (ITDs), has recently been incorporated into the molecular classification of ESS. BCOR, a transcriptional corepressor of BCL-6, contributes to tumor progression through its role in polycomb repressive complex 1 (PRC1), underscoring its importance in oncogenesis and potential as a therapeutic target. Advances in molecular diagnostics, such as next-generation sequencing (NGS) and fluorescence in situ hybridization (FISH), have improved the precision of diagnosing BCOR-altered ESS, enabling better prognostic stratification. These findings also support the development of targeted therapies, including CDK4/6 inhibitors and immunotherapies targeting PD-1 and CTLA-4 pathways. Despite these advancements, barriers such as limited access to molecular diagnostics and the high cost of novel therapies remain significant challenges. This review bridges molecular and clinical insights into ESS, emphasizing the diagnostic, prognostic, and therapeutic implications of BCOR rearrangements. By integrating these advances into clinical practice, it aims to improve outcomes for patients with this rare and aggressive malignancy.

High-grade endometrial stromal sarcoma with BCOR rearrangements: clinicopathological analysis of five cases and literature reviews - an extension in understanding of morphological characteristics

Five cases of FISH verified BCOR rearranged high-grade endometrial stromal sarcoma were retrospectively analyzed. The patient age ranged from 33 to 65 years (median, 48.4 years). Most patients presented with irregular vaginal bleeding (3/5) and uterus mass (2/5). Only one patient developed an abdominal wall metastasis and other patients remained in good condition during the follow-up. Pathological findings revealed that the tumors exhibited morphological diversity in terms of cell shape, arrangement pattern and tumor stroma, compared to previous summarized histology of BCOR rearranged high-grade endometrial stromal sarcoma. Detailed description of such morphology changes expanded our understanding of the histology of BCOR rearranged high-grade endometrial stromal sarcoma. Due to the non-specificity of morphology in such malignancies, molecular testing is needed for confirmation in all patients.

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.

Endometrial Stromal Sarcomas With BCOR Internal Tandem Duplication and Variant BCOR/BCORL1 Rearrangements Resemble High-grade Endometrial Stromal Sarcomas With Recurrent CDK4 Pathway Alterations and MDM2 Amplifications

The distinction between low-grade and high-grade endometrial stromal sarcomas (LGESS, HGESS) is increasingly defined by genetics. Recently, variant genomic alterations involving BCOR or BCORL1 have been reported in endometrial stromal sarcoma (ESS), although it remains unclear whether these justify a diagnosis of LGESS or HGESS. In this study, we describe clinicopathologic and molecular features of ESS with such alterations to help clarify their classification in the spectrum of ESS. We collected a cohort of 13 ESS harboring variant alteration involving BCOR (6 with internal tandem duplication, 1 with EP300::BCOR fusion, 1 with BCOR::LPP fusion) and BCORL1 ( 4 with JAZF1::BCORL1 fusion, 1 with EPC1::BCORL1 fusion). The median patient age at primary diagnosis was 51 years (range: 18 to 70 y). Median tumor size at primary diagnosis was 9.3 cm (range: 4.5 to 21 cm), and extrauterine disease spread (stage IIIB-C) was present in 27%. The tumors were composed of round to spindled cells with cellularity and cytologic atypia ranging from mild to marked and a median mitotic count of 18/10 HPFs (range: 2 to 85/10 HPFs). At least focally myopermeative growth was noted in 8/8 assessable cases. Of 12 patients with follow-up data (median: 25 mo), 4 patients died of disease and 3 were alive with recurrent disease. Unsupervised hierarchical clustering of DNA methylation data together with a large cohort of uterine mesenchymal tumors that included YWHAE::NUTM2 and Z C3H7B::BCOR HGESS and molecularly confirmed LGESS revealed a common methylation signature for all ESS with variant BCOR and BCORL1 alterations and HGESS with YWHAE::NUTM2 and ZC3H7B::BCOR gene fusion. Copy number analysis revealed amplifications of CDK4 and MDM2 , as well as homozygous deletions of CDKN2A/B and NF1 in a subset of tumors. Our results indicate that ESS with BCOR internal tandem duplication and variant BCOR and BCORL1 rearrangements clinically and molecularly resemble conventional HGESS.