OBJECTIVE: To review and analyze the clinical diagnosis and treatment of renal Ewing\'s sarcoma with venous tumor embolus, to follow up the survival and prognosis of the patients, and to provide help for the diagnosis and treatment of the disease.
METHODS: Clinical data (including general data, surgical data and postoperative pathological data) of patients diagnosed with renal Ewing\'s sarcoma with venous tumor embolus in Peking University Third Hospital from June 2016 to June 2022 were collected, and the prognosis of the patients was followed up to analyze the influence of diagnosis and treatment process on the prognosis of the disease.
RESULTS: There were 6 patients, including 1 male and 5 females. There were 4 cases of left renal tumor and 2 cases of right renal tumor. The median age at diagnosis was 28 years (16-52 years). The imaging findings were all exogenous tumors with internal necrotic tissue and hemorrhage. The mean maximum tumor diameter was 12.6 cm, and the mean tumor thrombus length was 7.8 cm. Four patients underwent open surgery and 2 patients underwent laparoscopic surgery. The postoperative pathological results were renal Ewing sarcoma. Immunohistochemical results showed 3 cases of CD99 (+), 2 cases of FLI-1 (+), and 1 case of CD99, FLI-1 (-). 3 patients received chemotherapy (cyclophosphamide, doxorubicin, vincristine/ifosfamide, etoposide), 1 case received chemotherapy combined with radiotherapy, and 2 cases received no adjuvant therapy. The mean overall survival (OS) of the 6 patients was 37 months, and the mean OS of the 4 patients (47 months) who received chemotherapy was significantly higher than that of the 2 patients (16 months) who did not receive chemotherapy (P=0.031).
CONCLUSIONS: Renal Ewing\'s sarcoma with venous tumor embolus is rare in clinic, and it is common in young female patients. The operation is difficult and the prognosis is poor. Surgical resection, adjuvant radiotherapy and chemotherapy can improve the overall survival rate of the patients.

Cluster of differentiation 99 (CD99) is a receptor that is significantly upregulated in acute myeloid leukemia (AML). FMS-like tyrosine kinase 3 internal tandem duplication mutation in AML (FLT3-ITD AML) exhibits even higher levels of CD99 expression. Our group previously employed a novel peptide platform technology called elastin-like polypeptides and fused it with single-chain antibodies capable of binding to FLT3 (FLT3-A192) or CD99 (CD99-A192). Targeting either FLT3 or CD99 using FLT3-A192 or CD99-A192 led to AML cell death and reduced leukemia burden in AML mouse models. Here, we report on the development of a novel Co-Assembled construct that is capable of binding to both CD99 and FLT3 and the antileukemia activity of the bispecific construct in FLT3-ITD AML preclinical models. This dual-targeting Co-Assembled formulation exhibits cytotoxic effects on AML cells (AML cell lines and primary blasts) and reduced leukemia burden and prolonged survival in FLT3-ITD AML mouse models. Altogether, this study demonstrates the potential of an innovative therapeutic strategy that targets both FLT3 and CD99 in FLT3-ITD AML.
UNASSIGNED: This study investigates a dual-targeting strategy in acute myeloid leukemia (AML), focusing on FLT3 and CD99. The approach demonstrates enhanced therapeutic potential, presenting a novel option for AML treatment.

BACKGROUND: Differences in immune responses between women and men are leading to a strong sex bias in the incidence of autoimmune diseases that predominantly affect women, such as multiple sclerosis (MS). MS manifests in more than twice as many women, making sex one of the most important risk factor. However, it is incompletely understood which genes contribute to sex differences in autoimmune incidence. To address that, we conducted a gene expression analysis in female and male human spleen and identified the transmembrane protein CD99 as one of the most significantly differentially expressed genes with marked increase in men. CD99 has been reported to participate in immune cell transmigration and T cell regulation, but sex-specific implications have not been comprehensively investigated.
METHODS: In this study, we conducted a gene expression analysis in female and male human spleen using the Genotype-Tissue Expression (GTEx) project dataset to identify differentially expressed genes between women and men. After successful validation on protein level of human immune cell subsets, we assessed hormonal regulation of CD99 as well as its implication on T cell regulation in primary human T cells and Jurkat T cells. In addition, we performed in vivo assays in wildtype mice and in Cd99-deficient mice to further analyze functional consequences of differential CD99 expression.
RESULTS: Here, we found higher CD99 gene expression in male human spleens compared to females and confirmed this expression difference on protein level on the surface of T cells and pDCs. Androgens are likely dispensable as the cause shown by in vitro assays and ex vivo analysis of trans men samples. In cerebrospinal fluid, CD99 was higher on T cells compared to blood. Of note, male MS patients had lower CD99 levels on CD4+ T cells in the CSF, unlike controls. By contrast, both sexes had similar CD99 expression in mice and Cd99-deficient mice showed equal susceptibility to experimental autoimmune encephalomyelitis compared to wildtypes. Functionally, CD99 increased upon human T cell activation and inhibited T cell proliferation after blockade. Accordingly, CD99-deficient Jurkat T cells showed decreased cell proliferation and cluster formation, rescued by CD99 reintroduction.
CONCLUSIONS: Our results demonstrate that CD99 is sex-specifically regulated in healthy individuals and MS patients and that it is involved in T cell costimulation in humans but not in mice. CD99 could potentially contribute to MS incidence and susceptibility in a sex-specific manner.
The immune system protects us from bacterial and viral infections and impacts the outcome of many diseases. Thus, understanding immunological processes is crucial to unravel pathogenic mechanisms and to develop new therapeutic treatment options. Sex is a biological variable affecting immunity and it is known that females and males differ in their immunological responses. Women mount stronger immune responses leading to more rapid control of infections and greater vaccine efficacy compared to men. However, this enhanced immune responsiveness is accompanied by female preponderance and susceptibility to autoimmune diseases like systemic lupus erythematosus, rheumatoid arthritis and multiple sclerosis (MS). MS sex ratio varies around 2:1 to 3:1 with a steadily increasing incidence in female MS patients making sex one of the top risk factors for developing MS. However, the underlying biological mechanisms including sex hormones as well as genetic and epigenetic factors and their complex interplay remain largely unknown. Here, we discovered the gene and its encoded protein CD99 to be differentially expressed between women and men with men showing increased expression on many immune cell subsets including T cells. Since T cells are key contributors to MS pathogenesis, we examined the role of CD99 on T cells of healthy individuals and MS patients. We were able to identify CD99-mediated T cell regulation, which might contribute to sex differences in MS susceptibility and incidence indicating the importance to include sex as a biological variable. Of note, these differences were not reproduced in mice showing the necessity of functional research in humans.

Ewing sarcoma is an uncommon neoplasm considered in the differential diagnosis of tumors with \"small round cell\" morphology, but its occurrence in the gynecologic tract has only been sporadically documented. Herein, we describe the largest cohort of Ewing sarcoma localized to the female genital tract to date, and emphasize their clinicopathologic resemblance to more common gynecologic neoplasms. Ewing sarcoma (n=21) was retrospectively identified from 5 institutions. The average patient age was 35 (range 6-61) years. Tumor sites included uterus (n=8), cervix (n=4), vulva (n=5), vagina (n=1), broad ligament (n=1), inguinal area (n=1), and pelvis (n=1). Nine of 18 cases in which slides were available for review demonstrated only classic round cell morphology, with the remainder showing a variable combination and prominence of variant ovoid/spindle or epithelioid appearance. Tumors showed diffuse membranous reactivity for CD99 (20/20) and were positive for NKX2.2 (8/8, diffuse) and cyclin D1 (7/7, of which 3/7 were patchy/multifocal and 4/7 were diffuse). They were negative for ER (0/6) and CD10 (0/6). Three cases were initially diagnosed as endometrial stromal sarcomas. EWSR1 rearrangement was confirmed in 20/21 by fluorescence in situ hybridization (n=15) and/or sequencing (n=8). Of the eight tumors that underwent sequencing, 6 harbored FLI1 , 1 ERG, and 1 FEV as the fusion partner. Of 11 patients with available follow-up, 5 died of disease, 1 developed lung metastases and 5 are alive with no evidence of disease. Ewing sarcoma of the gynecologic tract is a rare, aggressive entity that shares some morphologic and immunohistochemical features with other more common gynecologic neoplasms. In addition to the typical round cell appearance, variant spindled/ovoid to epithelioid morphology may also be observed and should prompt consideration of this entity with appropriate immunohistochemical and/or molecular studies.

目的： 探讨血管瘤样纤维组织细胞瘤的临床病理学及分子特征。 方法： 收集河南省儿童医院病理科2018—2022年血管瘤样纤维组织细胞瘤5例，总结分析临床特点、组织学及免疫组织化学结果，荧光原位杂交（FISH）及荧光PCR-毛细管电泳测序法检测相应基因改变并随访。 结果： 5例患儿中，男患儿3例，女患儿2例，年龄3~10岁。发病部位1例位于腋窝淋巴结区域，余4例位于皮下软组织。临床表现为进展缓慢的无痛性肿块，超声显示低回声包块，均予手术完整切除送病理检查。肿瘤最大径1.0~3.5 cm，切面灰白、质中，实性或囊性。组织学肿瘤均有纤维性包膜及淋巴细胞增生、聚集。肿瘤细胞梭形或卵圆形，编织状或弥漫片状分布，4例中可见核分裂象。囊性区未见上皮衬覆，囊内可见大量红细胞或片状坏死。免疫组织化学染色显示5例均表达结蛋白，4例表达CD99及平滑肌肌动蛋白（SMA），1例表达间变性淋巴瘤激酶（ALK，D5F3），Ki-67阳性指数4例约5%，1例约40%。FISH检测结果提示5例均存在EWSR1基因断裂，其中4例同时伴有CREB1基因断裂，表达ALK（D5F3）蛋白的病例不存在ALK基因断裂及突变。3例获随访资料，随访6~60个月，均未复发。 结论： 血管瘤样纤维组织细胞瘤属儿童罕见的中间型间叶源性肿瘤，常发生在头颈部、四肢躯干皮下软组织，病理形态多样，免疫表型常表达结蛋白、SMA及CD99，分子检测有助于明确诊断。偶见ALK蛋白表达。.

Glioblastoma is the most frequent and aggressive brain tumor in adults. This study aims to evaluate the expression and prognostic impact of CD99, a membrane glycoprotein involved in cellular migration and invasion. In a cohort of patients with glioblastoma treated with surgery, radiotherapy and temozolomide, we retrospectively analyzed tumor expression of CD99 by immunohistochemistry (IHC) and by quantitative real-time polymerase chain reaction (qRT-PCR) for both the wild type (CD99wt) and the truncated (CD99sh) isoforms. The impact on overall survival (OS) was assessed with the Kaplan-Meier method and log-rank test and by multivariable Cox regression. Forty-six patients with glioblastoma entered this study. Immunohistochemical expression of CD99 was present in 83%. Only the CD99wt isoform was detected by qRT-PCR and was significantly correlated with CD99 expression evaluated by IHC (rho = 0.309, p = 0.037). CD99 expression was not associated with OS, regardless of the assessment methodology used (p = 0.61 for qRT-PCR and p = 0.73 for IHC). In an exploratory analysis of The Cancer Genome Atlas, casuistry of glioblastomas CD99 expression was not associated with OS nor with progression-free survival. This study confirms a high expression of CD99 in glioblastoma but does not show any significant impact on survival. Further preclinical studies are needed to define its role as a therapeutic target in glioblastoma.

Ewing sarcoma (EWS) is an aggressive pediatric bone tumor characterized by unmet clinical needs and an incompletely understood epigenetic heterogeneity. Here, we considered CD99, a major surface molecule hallmark of EWS malignancy. Fluctuations in CD99 expression strongly impair cell dissemination, differentiation, and death. CD99 is also loaded within extracellular vesicles (EVs), and the delivery of CD99-positive or CD99-negative EVs dynamically exerts oncogenic or oncosuppressive functions to recipient cells, respectively. We undertook mass spectrometry and functional annotation analysis to investigate the consequences of CD99 silencing on the proteomic landscape of EWS cells and related EVs. Our data demonstrate that (i) the decrease in CD99 leads to major changes in the proteomic profile of EWS cells and EVs; (ii) intracellular and extracellular compartments display two distinct signatures of differentially expressed proteins; (iii) proteomic changes converge to the modulation of cell migration and immune-modulation biological processes; and (iv) CD99-silenced cells and related EVs are characterized by a migration-suppressive, pro-immunostimulatory proteomic profile. Overall, our data provide a novel source of CD99-associated protein biomarkers to be considered for further validation as mediators of EWS malignancy and as EWS disease liquid biopsy markers.

Ewing sarcoma (EWS) is the second most common pediatric bone tumor. The EWS tumor microenvironment is largely recognized as immune-cold, with macrophages being the most abundant immune cells and their presence associated with worse patient prognosis. Expression of CD99 is a hallmark of EWS cells, and its targeting induces inhibition of EWS tumor growth through a poorly understood mechanism. In this study, we analyzed CD99 expression and functions on macrophages and investigated whether the concomitant targeting of CD99 on both tumor and macrophages could explain the inhibitory effect of this approach against EWS. Targeting CD99 on EWS cells downregulated expression of the \"don\'t eat-me\" CD47 molecule but increased levels of the \"eat-me\" phosphatidyl serine and calreticulin molecules on the outer leaflet of the tumor cell membrane, triggering phagocytosis and digestion of EWS cells by macrophages. In addition, CD99 ligation induced reprogramming of undifferentiated M0 macrophages and M2-like macrophages toward the inflammatory M1-like phenotype. These events resulted in the inhibition of EWS tumor growth. Thus, this study reveals what we believe to be a previously unrecognized function of CD99, which engenders a virtuous circle that delivers intrinsic cell death signals to EWS cells, favors tumor cell phagocytosis by macrophages, and promotes the expression of various molecules and cytokines, which are pro-inflammatory and usually associated with tumor regression. This raises the possibility that CD99 may be involved in boosting the antitumor activity of macrophages.

Pilomatrixoma is a relatively rare benign skin appendageal tumor, often presenting in the pediatric age group as a nodular lesion and most commonly involving the head and neck, making it amenable to primary fine needle aspiration (FNA) diagnosis. We report the clinical and histopathological findings of two cases of pilomatrixoma in children, both of which were initially misdiagnosed as small round blue cell tumors due to high cellularity and misinterpretation of the proliferating basaloid cells. Histopathology revealed basal cell proliferation and mitoses indicating that they were progressive, early lesions. The first case showed membranous positivity for CD99 which prompted a diagnosis of Ewing sarcoma. Awareness of the morphological spectrum including positivity for CD99 and careful evaluation of cell block histology could have averted the misdiagnosis. Pilomatrixoma should be included as an important differential diagnosis when faced with primitive-appearing cells on FNA, especially in children with mass lesions in the head and neck region.

Immunohistochemistry plays a vital role in the diagnosis of small round cell tumors. CD99 immunonegativity is one of the features, which helps in distinguishing neuroblastoma from other small round cell tumors. NKX2.2 is a specific marker of Ewing sarcoma, which is a differential for poorly differentiated neuroblastoma. Here, we present a case of metastatic neuroblastoma showing immunoreactivity for both CD99 and NKX2.2 on cytology of the metastatic site causing diagnostic dilemma. Biopsy study of the adrenal lesion revealed presence of differentiating cells and neuropil, highlighting the importance of evaluation of the primary site and limitation of cytology.