# Low-grade endometrial stroma-like sarcoma with smooth-muscle-like differentiation, DOG1 expression and JAZF1::SUZ12 fusion in a male patient

Pierre Allaume, Louis Escuer, Sébastien Henno, Aude Merdrignac, Cyrille

Berra, Frederic Dugay, François Le Loarer, Solene-Florence

Kammerer-Jacquet, Francisco Llamas Gutierrez

► To cite this version:

Pierre Allaume, Louis Escuer, Sébastien Henno, Aude Merdrignac, Cyrille Berra, et al. Low-grade endometrial stroma-like sarcoma with smooth-muscle-like differentiation, DOG1 expression and JAZF1::SUZ12 fusion in a male patient. Human Pathology Reports, 2025, 42, pp.300808. 10.1016/j.hpr.2025.300808. hal-05423777

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# Low-grade endometrial stroma-like sarcoma with smooth-muscle-like differentiation, DOG1 expression and *JAZF1::SUZ12* fusion in a male patient

Pierre Allaume<sup>a,\*</sup>, Louis Escuer<sup>a</sup>, Sébastien Henno<sup>a</sup>, Aude Merdrignac<sup>b</sup>, Cyrille Berra<sup>c</sup>, Frédéric Dugay<sup>d</sup>, François Le Loarer<sup>e</sup>, Solène-Florence Kammerer-Jacquet<sup>a</sup>, Francisco Llamas-Gutierrez<sup>a</sup>

## ARTICLE INFO

### Keywords:

Endometrial Stroma Sarcoma
Mesenchymal Tumor
DOG1
JAZF1
SUZ12

## ABSTRACT

Low-grade endometrial stromal sarcoma (LG-ESS) is an uncommon mesenchymal tumor typically arising in the uterine corpus, but has been rarely described in men. We present a case of a molecularly confirmed LG-ESS in a 60-year-old male patient, presenting as a pelvic mass with oligo-symptoms. The core-needle tumor sample demonstrated histological features of a low-grade fusocellular tumor with partial smooth muscle differentiation, strongly positive for smooth muscle actin and desmin, and weak DOG1 expression. Molecular analysis identified a JAZF1::SUZ12 gene fusion, akin to LG-ESS. This case underscores the potential challenge of diagnosing LG-ESS in men, where differential diagnoses include other tumors of mesenchymal origin such as gastrointestinal stromal tumors (GISTs) and solitary fibrous tumors, among others. As DOG1 expression in LG-ESS hasn't been reported in the literature yet, we retrospectively performed DOG1 immunohistochemistry of eight cases LG-ESS in women, finding DOG1 expression in 50% of cases with a weak and heterogeneous pattern. This novel finding highlights a potential pitfall in the diagnosis of LG-ESS especially in men, and warrants further investigations.

## Introduction

Low-grade endometrial stromal sarcoma (LG-ESS) is an infrequent, low-grade malignant neoplasm that shares histological similarities with proliferative-phase endometrial stroma. It primarily occurs in the uterine corpus but can also present in extra-uterine locations [1]. According to the fifth edition of the World Health Organization (WHO) classification, LG-ESS is categorized under “endometrial stromal and related tumors,” which also includes Endometrial Stromal Nodule (ESN), High-grade Endometrial Stromal Sarcoma (HG-ESS), and Undifferentiated Uterine Sarcoma (UUS) [2]. LG-ESS exhibits an indolent behaviour and an excellent 5-year and 10-years survival rate. The standard treatment approach involves total hysterectomy and bilateral salpingo-oophorectomy; however, ovary-sparing and even uterine-preserving surgeries have been proposed, particularly for younger patients

desiring fertility preservation [3,4].

Morphologically, LG-ESS displays a broad spectrum of histopathological patterns, ranging from those resembling ESN to more aggressive HG-ESS-like features [5]. Some tumours can show others components such as smooth muscle, foamy histiocytes, sex-cords elements and epithelioid, myxoid or rhabdoid changes, and while skeletal muscle and adipocytic metaplasia have been described in a few cases, they have not been documented in molecularly confirmed instances [5-7]. Mitotic activity is variable. The intra-tumoral vascularisation is relatively rich and well-organized, boasting both thin-walled and thick-walled, small to medium-sized vessels [8]. In immunohistochemistry, LG-ESS is usually positive for CD10 (diffusely), oestrogen and progesterone receptors, and BCL1/cyclineD1 (focal) [2]. Interestingly, although of mesenchymal origin, some LG-ESS show cytoplasmic positivity for cytokeratins [9]. Depending on the presence of smooth muscle or sex-cords elements,

<footnote><sup>a</sup> Department of Pathology, Rennes University Hospital, Rennes, France</footnote>

<footnote><sup>b</sup> Department of Hepatobiliary and Digestive Surgery, Rennes University Hospital, Rennes, France</footnote>

<footnote><sup>c</sup> Department of Molecular Biology, Rennes University Hospital, Rennes, France</footnote>

<footnote><sup>d</sup> Department of Cytogenetics, Rennes University Hospital, Rennes, France</footnote>

<footnote><sup>e</sup> Bergonié Institute, Unicancer Nouvelle-Aquitaine, Bordeaux, France</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: Pierre.AllAUME@chu-rennes.fr (P. Allaume).</footnote>
desmin/caldesmon and WT1/inhibin/calretinin staining, respectively, may be observed as well.

The distinction between low-grade and high-grade endometrial stromal sarcoma is based first on morphology [10]. Contrary to LG-ESS, HG-ESS may present more prominent atypia, a myxoid matrix, areas of necrosis and lymphovascular invasions; sometimes appearing undifferentiated [11]. Interestingly, both LG-ESS and HG-ESS present a uniform appearance, due to simple underlying genetic alterations. Indeed, recent advances in the molecular characterization of Endometrial Stroma Sarcomas show different driving molecular alterations between ESN/LG-ESS and HG-ESS, supporting distinct oncogenetic mechanisms [12]. LG-ESS mostly shows gene fusions involving JAZF1, most commonly JAZF1::SUZ12 [13,14]. JAZF1 encodes a transcriptional-repressor protein, while SUZ12 codes for a sub-unit of the polycomb regulation complex 2 (PRC2), responsible for histone H3 methylation on lysine 27 (resulting in the epigenetic modification H3K27me3) [15]. Other genes coding for transcriptional-repressor protein (such as PHF1) or proteins participating to the PRC (such as EPC1/2, MEAF6, MBTD1 or EZHIP) were also found to be rearranged in one or another combination in LG-ESS [12]. Meanwhile, HG-ESS are subdivided in two groups depending of their molecular anomalies, with either an alteration of the BCL-6 corepressor gene BCOR (with a wide array of partners) or of the gene YWHAE (especially YWHAE::NUTM2A) [16]. Of note, NTRK fusions have also been described [17]. Hence, these different alterations concur to distinct DNA methylation profiles, supporting LG- and HG-ESS as different entities altogether [18].

LG-ESS are infrequently encountered in routine pathology. We report a case of a molecularly confirmed JAZF1::SUZ12 translocated mesenchymateous tumour arising in a 60 years old male patient without any clinical history, manifesting as a pelvic mass. As LG-ESS are exceptionally described in men, we thoroughly investigated differential diagnosis and found a faint expression of DOG1. Up to this date, cells of endometrial stromal origin were not reported to express DOG1 [19,20]. Therefore, we further investigated DOG1 expression into eight LG-ESS cases retrospectively collected from our archives.

## Material and methods

### Radiology

Thoraco-abdomino-pelvic CT-scan was acquired with a Scanner SIEMENS Somatom Definition AS 128. Magnetic Resonance Imaging (MRI) was acquired with a SIEMENS MAGNETOM AMIRA BIOMATRIX.

### Pathology

Histological samples were fixated in formaldehyde 4 % and embedded in paraffin. Four-mm-thick whole-tissue sections were cut and mounted on glass slides (Superfrost+, Menzel Glazer). Slides were stained in Hematoxylin-Eosin-Safran and immunostained using Ventana Benchmark XT. DOG1 immunohistochemical study was performed with anti-DOG1 antibody (clone sp31-Cell Marque, Roche). All slides were digitalized and reviewed using Philips Intellisite Pathology Suite (Philips).

### Molecular analysis

All molecular analysis were performed on paraffine-embedded samples. BRAF, KIT and PDGFRA alterations were investigated by Next Generation Sequencing, library production by Juno, Fuidigm, and sequencing by NextSeq, Illumina, genome reference hg38. ARN fusions were investigated by Next Generation Sequencing, library production by FusionPlex, Archer, and sequencing by MiSeq, Illumina, genome reference hg19. JAZF1 rearrangement was additionally studied in Fluorescence In Situ Hybridation (FISH) on a four-mm-thick paraffin-embedded whole-tissue sections with a break-apart probe Locus Specific Identifier

JAZF1 (7p15.1-15.2) Dual Color Break Apart (Zytolight). Positive cut-off was set at > 15 % of rearranged nuclei.

## Patients consent and ethical statements

The clinician obtained written informed consent for the patient presented in this study. For patients whose histological data were retrospectively investigated for DOG1 expression, non-opposition was warranted as per local guidelines (MR-004 Rennes University Hospital). This study was conducted in appliance with the Declaration of Helsinki.

## Case report and study

### Clinical presentation

A 60-years old male patient presented oligo-symptoms expressed as atypical chronic lombalgia, without general alteration. Ultrasonic echography was performed and described a circumscribed pelvic mass in need of further explorations.

### Radiological findings

Patient underwent thoraco-abdomino-pelvic CT-scan and MRI. CT-scan and MRI found a tissular mass, enhanced after injection, located anterior to the rectum, posterior to the bladder and superior to the prostate (Fig. 1). This mass measured approximately 84 x 67 x 63 mm, appeared well circumscribed and rich in blood vessels after injection, without any sign of mesorectal fascia infiltration. The mass pushed the prostate and the seminal glands forward and the rectum backward, without infiltration; a thin slice of fat was preserved between the mass and the adjacent structures. A tumour of mesenchymal origin was suspected.

### Pathological and molecular findings on core needle biopsy

Four scanno-guided 16G core needle biopsies were addressed to the pathology laboratory. These biopsies were between 12 and 15 mm length, fixed in formol and stained with Hematoxylin-Eosin-Safran. We observed a tumour proliferation of varying cellularity, with densely cellular areas organised in intertwined cells currents. Tumour cells appeared quite monomorphous, without major atypia, fusiform with oval nuclei and vesicular chromatin, and amphophile cytoplasm (Fig. 2). There was no mitosis, no necrosis nor myxoid or chondromatoid areas. Immunohistochemical study was performed. The tumour stained diffusely for smooth muscle actin, heterogeneously for desmin and caldesmon. Focal expression of DOG1 was observed. The tumour cells were negative for CKAE1/AE3, EMA, CD34, myoD1 and myogenin, as well as CD117, STAT6 and MDM2. Proliferation index by Ki-67 was low, around 1 to 3 % depending on the areas.

Based on these findings, we concluded to a tumour with fusiform cells without histological criteria of aggressivity, of uncertain diagnosis. Morphology associated with a focal expression of DOG1 raised the hypothesis of a Gastro-Intestinal Stromal Tumour (GIST), although not typical. In order to better classify this tumour, a molecular study of BRAF, KIT (exons 9, 11, 13, 14 and 17) and PDGFRA (exons 12, 14 and 18) was performed, as well as RNA-sequencing. A fusion between exon 03 of JAZF1 and the exon 02 of SUZ12 was identified by the analysis in RNA-sequencing: {JAZF1 (NM_175061.4));{SUZ12 (NM_015355.4)}. There was no alteration of BRAF, KIT and PDGFRA. Pluridisciplinar session recommended surgical resection without additional treatment.

### Pathological and molecular findings on resected tumour

A monobloc sample measuring 85 x 70 x 50 mm was addressed to the pathology laboratory. The sample was entirely tumoral, with a thinly encapsulated, well-circumscribed lesion. Cut-section demonstrated a
<figure><img src="image_3.png" /><figcaption>**Fig. 1.** Radiological appearance of the pelvic mass. A: MRI T1, axial, non-injected. B: MRI T1, axial, after contrast-enhancing injection, arterial time. A heterogeneous post-injection enhancement is observed. C: MRI, sagittal, T2. The rectum is pushed back and shows signs of distress (red arrow). D: CT-scan, axial, non-injected. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

fasciculate, homogenous, yellow to tan coloured aspect, without areas of overt necrosis (Fig. 3). In microscopy, the aspects were quite similar to that of the core needle biopsy. The proliferation was accompanied by a densely fibro-collagenous stroma, without inflammatory cells. Based on the hypothesis of a low-grade endometrial stroma-like sarcoma, complementary immunohistological study was performed. The tumour cells stained diffusely positive for CD10 and weakly and heterogeneously for oestrogen and progesterone receptors. Cytoplasmic (thus, negative) staining for WT1 was observed. Additionally, inhibinA, cyclineD1/BCL1 and calretinin were also negative.

The JAZF1::SUZ12 fusion we identified was predicted to impair trimethylation of histone H3K27 by downregulating the Polycomb Repressive Complex 2 protein (Fig. 4A and B). A study in fluorescence in-situ hybridation with a JAZF1 break-apart probe demonstrated a break-up pattern, thus illustrating JAZF1 rearrangement (Fig. 4C). We performed an immunohistochemistry study on the tumor with the anti-H3-ME antibody and observed a reduced expression compared to background inflammatory cells, demonstrating its phenotypic repercussion (Fig. 4D). Integrating all these findings, we concluded to a low-grade endometrial stroma-like sarcoma, arising in a male patient. The patient was followed up without post-surgical complications nor relapse to this day. Pluridisciplinar session recommended trimestrial follow-up with concomitant CT-scan.

DOG1 immunohistochemical staining on retrospectively collected cases non-tumoral endometrial stroma and LG-ESS

Eight cases of LG-ESS arising in women were retrospectively collected from our archives at the University Hospital of Rennes, and DOG1 immunohistochemistry was performed. Out of these eight cases, n = 4 (50 %) stained for DOG1 with a weak and heterogeneous expression pattern (whereas the positive control, a GIST, stained

strongly and diffusely), in the same manner as our reported case arising in a male patient.

Discussion

The diagnosis of LG-ESS is challenging on core needle biopsies and requires careful elimination of its many differential diagnosis. In women, the differential diagnosis of LG-ESS includes HG-ESS, gland-poor adenomyosis, cellular leiomyoma, intravascular leiomyomatosis, leiomyosarcoma with extensive intravascular component, uterine tumours resembling ovarian sex-cord tumour (UTROSCT), adenosarcoma and perivascular epithelioid cell tumour (PECOMA) [6]. Endometrial Stromal Nodules are not a pertinent differential diagnosis in men, since they do not arise outside of the uterine corpus by definition [2]. In cases with cytokeratin positivity, a carcinosarcoma may also be discussed. In men, LG-ESS are exceptional and do not come to mind first when discussing tumours of mesenchymal origin. Rather, confronted to a tumor arising in the pelvic region, with a monotonous proliferation of oval/fusiform cells and bland cytology, a pathologist may first evoque a dedifferentiated liposarcoma, a solitary fibrous tumor, a Gastro-Intestinal Stromal Tumor, or a low-grade smooth muscle tumor, among others. While strong DOG1 expression is considered specific of GIST, we showed that it may also be expressed, although faintly and heterogeneously, in some LG-ESS, a fact that was not described prior to this study; further investigations will be needed in order to assess the usefulness of DOG1 immunohistochemistry in the diagnosis of LG-ESS. Molecular study by targeted RNA-sequencing was, in our case, key to the diagnosis. Not only did it highlight the JAZF1::SUZ12 rearrangement, but it also provided arguments against differential diagnosis such as solitary fibrous tumor (lack of NAB2-STAT6 fusion) and desmoplastic round cell tumor (lack of EWSR::WT1 fusion). FISH additionally ruled out dedifferentiated liposarcoma (lack of MDM2 amplification).
<figure><img src="image_4.png" /><figcaption>**Fig. 2.** Histological appearance of the pelvic tumor, with HES-stain and key immunohistochemical studies. The tumour stained diffusely and strongly for actin and heterogeneously for desmin. Heterogenous and faint expression of DOG1 was observed. The tumour cells were negative for CD34, CD117, PS100, myogenin and myoD1.</figcaption></figure>

LG-ESS in men have been seldom reported in the literature. Agaimy et al. were the first to report such a case in a male patient presenting an intra-scrotal mass [21]. Pathological examination was similar to our case, and molecular analysis was also determinant for diagnosis, high-lighting the *JAZF1::SUZ12* fusion. In a study aiming to better subtype

tumors priorly diagnosed as prostatic stromal sarcomas and stromal tumors of uncertain malignant potential (STUMP) in men, Acosta et al. reclassified one STUMP in LG-ESS by demonstrating the *JAZF1::SUZ12* rearrangement by molecular analysis [22]. Finally, Dermawan et al. reported two cases of *para*-testicular and pelvic (same as our case) LG-
<figure><img src="image_5.png" /><figcaption>**Fig. 3.** Macroscopic and histological appearance of the pelvic tumor, with HES-stain and key immunohistochemical studies. The tumour stained diffusely and strongly for CD10, whereas it was negative for WT1 (cytoplasmic expression only). ER (estrogen receptor) and PR (progesterone receptor) showed weak and heterogeneous staining.</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>**Fig. 4.** Illustration of the molecular aspects of the tumor. A: Schematic structures of the JAZF1 and SUZ12 genes. Red lines mark their respective break points. B: Resulting JAZF1::SUZ12 fusion gene. C: Representative field in fluorescent microscopy demonstrating a JAZF1 rearrangement with a break-apart probe (yellow asterisks). D: Representative field of the tumor with reduced/suppressed expression of H3K27 trimethylation, demonstrating the phenotypic repercussion of the identified JAZF1::SUZ12 fusion (H3-ME antibody, clone poly Diagenode/Diagenode). H3-ME expression is retained in the background inflammatory cells, providing internal control (red asterisk) (40X). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

ESS, harboring a JAZF1-PHF1 fusion and a JAZF1-GLI3 fusion respectively [23]. GLI3 is yet another gene coding for a transcription factor protein, interacting in the Sonic Hedgehog pathway [24]. The pelvic case (the one boasting the JAZF1-GLI3 fusion) presented a peritoneal and omental dissemination, as well as an increased mitotic activity (9 per 5 mm² and Ki67 around 40–50 %), inconsistent with a low grade sarcoma. Interestingly, this patient had a clinical history of GIST, illustrating the pertinence of the differential diagnosis with LG-ESS, even more so as DOG1 immunochemistry was negative but CD117 was described as faintly positive. Of note, a few HG-ESS arising in male patients have also been reported, with molecular demonstration of BCOR-MAML3 and ZC3H7B-BCOR fusions [25–27].

In women, extra-uterine LG-ESS are uncommon and occur over a wide age range; its risk factors include prolonged oestrogen or tamoxifen exposition and pelvic irradiation, and an association with endometriosis has been described [2,28–30]. Endometriosis is also rarely reported in men, essentially an incidental finding in the para-testis, the urinary tract or the peritoneum regions [31,32]. Although it is not impossible that LG-ESS in men arises from occult endometriosis lesions, pelvic irradiation for prostate/bladder cancer or androgen-deprivation therapies might also be risk factors.

In conclusion, our case is the fifth case reported in the literature of

LG-ESS arising in a male patient. All reported cases of LG-ESS in men arose in the fifth to seventh decades and were located in the peri-prostatic or peri-testicular area. They presented as a multinodular, variably dense proliferation of monotonous round to spindle cells and a varying degree of mitotic activity, and demonstrated JAZF1 fusions with varying partners. Molecular study is key to the diagnosis, and prognosis is good after complete excision although local recurrence is possible.

## Statement of significance

Low-grade endometrial stromal sarcoma (LG-ESS) is a well described, although uncommon, mesenchymal tumor arising in women. Exceptional occurrences were reported in men, with only four cases in the whole literature. This case report of a molecularly confirmed LG-ESS in a 60-year-old male expands the clinical spectrum of this tumor and highlights its diagnostic challenges, especially in differentiating it from other mesenchymal neoplasms such as gastrointestinal stromal tumors (GISTs), among other. Importantly, we report, for the first time, DOG1 expression in LG-ESS, a marker typically associated with GIST, which may lead to diagnostic pitfalls. Additionally, we performed a retrospective study of DOG1 expression in eight cases of LG-ESS arising in women, and confirmed that DOG1 can stain (in a weak and
heterogenous pattern) in some cases of LG-ESS. This case emphasizes the
critical role of molecular diagnostics in the accurate classification of
mesenchymal tumors arising in the pelvic region in men, and suggests
that further studies may be needed to assess the diagnostic interest of
DOG1 expression in LG-ESS.

Patient consent statement

The patient provided written consent for the publication of this case
report.

CRediT authorship contribution statement

**Pierre Allaume:** Writing – review & editing, Writing – original draft, Methodology, Data curation, Conceptualization. **Louis Escuer:** Writing – review & editing, Writing – original draft. **Sébastien Henno:** Writing – review & editing, Data curation. **Aude Merdrignac:** Writing – review & editing, Validation, Data curation. **Cyrille Berra:** Writing – review & editing, Data curation. **Frédéric Dugay:** Writing – review & editing, Data curation. **François Le Loarer:** Writing – review & editing, Data curation. **Solène-Florence Kammerer-Jacquet:** Writing – review & editing, Supervision. **Francisco Llamas-Gutierrez:** Writing – review & editing, Supervision, Methodology, Data curation, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.

Acknowledgements

None.

Ethics statement including patient consent statement

The clinician obtained written informed consent for the patient
presented in this study. For patients whose histological data were
retrospectively investigated for DOG1 expression, non-opposition was
warranted as per local guidelines (MR-004 Rennes University Hospital).
This study was conducted in appliance with the Declaration of Helsinki.

Financial support

No funding source to disclose.

Data availability

Data will be made available on request.

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