MIC2 Gene Research Articles

Ewing's sarcoma/primitive neuroectodermal tumor arising from the adrenal gland: a case report and literature review.

We report a rare case of Ewing's sarcoma (ES)/primitive neuroectodermal tumor (PNET) arising from the adrenal gland. A 17-year-old Japanese woman presented with left upper abdominal pain and high fever. Computed tomography and magnetic resonance imaging revealed a 15 × 10 cm tumor replacing the adrenal gland. Preoperative diagnosis was an adrenocortical carcinoma. Resection of the tumor was performed. We obtained the final diagnosis of ES/PNET by immunohistochemical molecular study with positive staining for the MIC2 gene product (CD99) and a Ewing sarcoma breakpoint region 1 (EWSR1) gene rearrangement. Local recurrence was observed one month after the surgery. The patient was then treated with systemic chemotherapy and localized radiotherapy.

Unusual Genetic Aberrations Including a Deletion of KLF6 Tumor Suppressor Gene Revealed by Integrated Cytogenetic Approaches in a Pediatric Ewing Sarcoma

Ewing sarcoma is the third most common sarcoma in children and young adults. Its characteristic chromosomal rearrangement results in a chimerical EWSR1-ETS transcription factor. Secondary genetic alterations are very common. Membranous expression of CD99 is seen in almost all tumors. We report 2 unusual cytogenetic findings in a pediatric Ewing sarcoma, an insertion of the MIC2 gene encoding CD99 from Xp to 10p and a submicroscopic deletion of the well-known tumor supressor gene KLF6. The latter has not been described previously in pediatric neoplasms. Molecular pathways in tumorigenesis and genetic complexity in cancer are discussed.

CD99 suppresses osteosarcoma cell migration through inhibition of ROCK2 activity

CD99, a transmembrane protein encoded by MIC2 gene is involved in multiple cellular events including cell adhesion and migration, apoptosis, cell differentiation and regulation of protein trafficking either in physiological or pathological conditions. In osteosarcoma, CD99 is expressed at low levels and functions as a tumour suppressor. The full-length protein (CD99wt) and the short-form harbouring a deletion in the intracytoplasmic domain (CD99sh) have been associated with distinct functional outcomes with respect to tumour malignancy. In this study, we especially evaluated modulation of cell-cell contacts, reorganisation of the actin cytoskeleton and modulation of signalling pathways by comparing osteosarcoma cells characterised by different metastasis capabilities and CD99 expression, to identify molecular mechanisms responsible for metastasis. Our data indicate that forced expression of CD99wt induces recruitment of N-cadherin and β-catenin to adherens junctions. In addition, transfection of CD99wt inhibits the expression of several molecules crucial to the remodelling of the actin cytoskeleton, such as ACTR2, ARPC1A, Rho-associated, coiled-coil containing protein kinase 2 (ROCK2) as well as ezrin, an ezrin/radixin/moesin family member that has been clearly associated with tumour progression and metastatic spread in osteosarcoma. Functional studies point to ROCK2 as a crucial intracellular mediator regulating osteosarcoma migration. By maintaining c-Src in an inactive conformation, CD99wt inhibits ROCK2 signalling and this leads to ezrin decrease at cell membrane while N-cadherin and β-catenin translocate to the plasma membrane and function as main molecular bridges for actin cytoskeleton. Taken together, we propose that the re-expression of CD99wt, which is generally present in osteoblasts but lost in osteosarcoma, through inhibition of c-Src and ROCK2 activity, manages to increase contact strength and reactivate stop-migration signals that counteract the otherwise dominant promigratory action of ezrin in osteosarcoma cells.

Ewing's Sarcoma/Primitive Neuroectodermal Tumor Arising from the Adrenal Gland: A Case Report and Literature Review

We report a rare case of Ewing's sarcoma (ES)/primitive neuroectodermal tumor (PNET) arising from the adrenal gland. A 17-year-old Japanese woman presented with left upper abdominal pain and high fever. Computed tomography and magnetic resonance imaging revealed a 15 × 10 cm tumor replacing the adrenal gland. Preoperative diagnosis was an adrenocortical carcinoma. Resection of the tumor was performed. We obtained the final diagnosis of ES/PNET by immunohistochemical molecular study with positive staining for the MIC2 gene product (CD99) and a Ewing sarcoma breakpoint region 1 (EWSR1) gene rearrangement. Local recurrence was observed one month after the surgery. The patient was then treated with systemic chemotherapy and localized radiotherapy.

Abstract 4325: CD99 suppresses osteosarcoma cell migration by favouring the oncosoppressor N-cadherin/beta-catenin signalling pathway in contrast to ezrin.

Abstract CD99 is a 32-kDa highly glycosylated transmembrane protein encoded by MIC2 gene which shares no homology with any known family of proteins except Xga and mouse CD99L2 proteins. Located in the pseudoautosomal region of chromosomes X and Y, MIC2 encodes two distinct products by alternative splicing of gene transcripts: a long form (32-kDa), corresponding to the full-length protein (CD99wt) and a short form harbouring a deletion in the intracytoplasmic domain (CD99 sh). CD99 is involved in multiple cellular events including cell adhesion, apoptosis, differentiation of T- cells and thymocytes, transendothelial migration of leukocytes, maintenance of cellular morphology and regulation of intracellular membrane protein trafficking either in physiology and in pathological conditions. In osteosarcoma, CD99 is expressed at low levels and functions as a tumor suppressor. The two alternative spliced isoforms are associated to distinct functional outcomes: CD99sh expression increases, whereas wtCD99 significantly inhibits migration, invasiveness and metastasis of osteosarcoma cells (Manara MC, 2006; Scotlandi K 2007). In this study, we specifically analyzed modulation of cell-cell contacts, reorganization of the actin cytoskeleton, and modulation of signalling pathways by comparing osteosarcoma cells characterized by different metastasis capabilities and CD99 expression, to identify molecular mechanisms responsible for metastasis. Our data indicate that expression of CD99wt induces recruitment of beta-catenin to adherens injunctions through N-cadherin up-regulation. In addition, forced expression of CD99wt inhibits the expression of several molecules crucial to remodeling the actin cytoskeleton, such as ACTR2 (also named ARP2), ARPC1A and ROCK II as well as ezrin, an ezrin/radixin/moesin (ERM) family member that has been clearly associated with tumor progression and metastatic spread either in experimental models and clinical samples of osteosarcoma. Functional studies by siRNA and/or specific inhibitors point to ROCKII as a crucial intracellular mediator regulating osteosarcoma metastasis capabilities. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4325. doi:1538-7445.AM2012-4325

CD99 triggers upregulation of miR‐9‐modulated PRDM1/BLIMP1 in Hodgkin/Reed–Sternberg cells and induces redifferentiation

CD99 is a 32-kDa transmembrane glycoprotein that is encoded by the MIC2 gene. Our study was carried out to examine the role of CD99 in tumor progression of classical Hodgkin lymphoma (cHL). Here, we showed that lowly expressed CD99 protein in cHL cell lines and primary cHL cases correlates with the deficient expression of the positive regulatory domain 1 (PRDM1/BLIMP1). In addition, cHL cell lines showed high levels of miR-9 expression. We determined that the upregulation of CD99 induced expression of transcription factor PRDM1, a master regulator of plasma-cell differentiation, which is also a target for miR-9-mediated downregulation. Indeed, inhibition of miR-9 also triggered upregulation of PRDM1 expression. Furthermore, overexpression of CD99 resulted in changed growth features and reorganization of actin cytoskeleton. As upregulation of CD99 led to a decrease in cHL diagnosis marker CD30 and CD15 and an increase in plasma-cell differentiation marker CD38 and the restoration of B-cell makers PAX5, CD79α and CD19, we suggest that downregulated CD99 leads to the prevention of plasma-cell differentiation in Hodgkin/Reed-Sternberg (H/RS) cells. Furthermore, these data indicate that CD99 may control miR-9 expression, which directly targets PRDM1. Altogether, these results reveal a CD99-miR-9-PRDM1 molecule axis in lymphomagenesis of cHL and suggest that upregulation of CD99 in H/RS cells induces terminal B-cell differentiation, which may provide a novel therapeutic strategies for cHL.

Primitive neuroectodermal tumor/Ewing’s sarcoma of the urinary bladder: a case report and its molecular diagnosis

We report a rare case of primitive neuroectodermal tumor/Ewing's sarcoma (PNET/ES) arising from the urinary bladder. A 65-year-old man presented with hematuria and dysuria. Computed tomography revealed an enlarged invasive tumor at the base of the bladder. No additional abnormal findings were disclosed by other diagnostic imaging methods. The surgical specimens showed small round cell tumor with positive staining for MIC2 gene product (CD99). EWS-FLI1 fusion transcripts were detected by reverse transcriptase polymerase chain reaction and direct sequencing, confirming the diagnosis of PNET/ES. The patient developed swollen pelvic lymph nodes as well as multiple lung metastases at 8months postoperatively. No effective results could be obtained even with systemic chemotherapy consisting of vincristine, ifosfamide, doxorubicin and etoposide (VIDE) based on the EUROpean Ewing tumour Working Initiative of National Groups 1999 (EURO-E.W.I.N.G. 99) multinational trial. The patient died of acute superior mesenteric artery thrombosis at 22months postoperatively. PNET/ES could have been included in past cases of small cell carcinoma because of the difficulty in its differential diagnosis. Exact diagnosis is crucial for deciding the treatment strategy for rare bladder tumors consisting of small round cells.

Primary primitive neuroectodermal tumor of the orbit

Primitive neuroectodermal tumor (PNET) is a small round cell malignant tumor of neuroectodermal origin. Most of the PNETs occur in the central nervous system (CNS). PNETs recognized outside of CNS are diagnosed as peripheral PNET (pPNET). This tumor which expresses MIC-2 gene (CD99) seems to be least aggressive after complete tumor resection. We describe a rare case of PNET in a young girl.

Regulation of porcine classical and nonclassical MHC class I expression

Major histocompatibility complex (MHC) class I molecules comprise a family of polymorphic cell surface receptors consisting of classical 1 a molecules that present antigenic peptides and nonclassical 1 b molecules. Gene expression for human classical and nonclassical MHC class I molecules has been shown to be differentially regulated by interferon, with variation in the nucleotide sequence of promoter regions, resulting in differences in interferon inducibility and basal levels of gene transcription. In this study on porcine classical and nonclassical swine leukocyte Ag (SLA) class I molecules, we show alignments of putative regulatory elements in the promoters of the three functional classical class I genes, SLA-1, SLA-2, and SLA-3; two nonclassical 1 b genes, SLA-6 and SLA-7; and a MIC-2 gene. Promoter elements were cloned upstream from a luciferase reporter gene, and the basal and inducible activities of each were characterized by expression in Max cells, an immortalized pig cell line that responds to interferon and tumor necrosis factor alpha (TNF-alpha). All three classical class I but not nonclassical promoters responded to interferon. This was confirmed by the transactivation of SLA-1, but not SLA-7, after the co expression with interferon regulatory factors (IRFs), IRF-1, IRF-2, IRF-3, IRF-7, and IRF-9. Classical class I genes were activated by cotransfection with nuclear factor kappa B (NF-kappaB) p65 and by treatment of cells with TNF-alpha, although, unlike human promoter there was no synergistic effect with interferon. The greatest effect on classical class I promoters was coexpression with the class II transactivator (CIITA), important for constitutive transactivation. These results determine the differential regulation of porcine classical and nonclassical MHC class I and reflects their importance in antigen presentation during infection.

MIC gene polymorphism and haplotype diversity in rhesus macaques

Rhesus macaques (Macaca mulatta) mainly originating from India were analysed for their major histocompatibility complex class I-related (MIC) gene repertoire. Thus far, three distinct genes, designated MIC1, MIC2 and MIC3, have been identified in the rhesus macaque. In addition, an MICD pseudogene has been described mapping apart from the other loci in a telomeric direction. Genomic comparisons and the presence of a characteristic microsatellite in exon 5 suggest that the MIC1 gene is the equivalent of the human MICA gene. Hence, the MIC2 gene, lacking the microsatellite - as do humans -, is considered to be the equivalent of human MICB. The MIC3 gene, a hybrid of MICA and MICB, seems to be generated by a crossing-over event with one breakpoint in intron 3 and accordingly is named MICA/B. Apart from their human counterparts, MICA, MICB and MICA/B cluster in separate branches in the phylogenetic tree, confirming the hybrid character of the MICA/B gene. Population analyses have shown that the various genes display polymorphism, and six MICA, five MICB and three MICA/B alleles have been identified. In the panel of homozygous typing cells, two distinct haplotype configurations have been defined by segregation analyses. Each haplotype comprises an MICB gene in conjunction with either an MICA or an MICA/B gene. Furthermore, the presence of a polymorphic microsatellite in the MICA and MICA/B alleles facilitates speedy and accurate haplotyping.

Toxoplasma gondii: DNA vaccination with genes encoding antigens MIC2, M2AP, AMA1 and BAG1 and evaluation of their immunogenic potential

A combination of antigenic regions of microneme proteins have been previously reported as being protective against chronic toxoplasmosis. In this work, we evaluated immune responses induced by immunizing BALB/c and C57BL/6 mice intradermally with plasmid DNA encoding the protein sequences of Toxoplasma gondii AMA1, MIC2, M2AP and BAG1. Mice immunized with the AMA1 gene developed high levels of serum IgG2a and c antibodies as well as cellular immune responses associated with IFN-γ synthesis suggesting a modulated Th1 type of response. Immunization with the AMA1 gene resulted in a partial but significant protection against the acute phase of toxoplasmosis compared to MIC2, M2AP and BAG1 genes. Therefore, the AMA1 gene appears to generate a strong specific immune response and also provides effective protection against toxoplasmosis more than the MIC2, M2AP and BAG1 genes.

Immunoreactivity of CD99 in invasive malignant melanoma

CD99, also known as p30/32, is a glycoprotein product of the MIC2 gene. It was originally utilized in immunohistochemistry as a unique marker for Ewing sarcoma, other primitive neuroectodermal tumors, and subsequently in other tumors. Its expression in malignant melanoma (MM) has not been well documented, with just two isolated cases of MM recently reported. Recent studies have documented CD99 expression in a significant percentage of atypical fibroxanthomas (AFX), posing potential diagnostic problems in differentiating these two entities. As mistaking MM for AFX based on immunohistochemical staining pattern has significant consequences, we sought to determine the percentage of invasive MM in our archives that have this staining pattern. Seventy-eight cases of invasive melanoma were retrieved from our files. Each case was stained with mouse anti-human CD99 and evaluated for membranous expression. Our evaluation revealed that 47 of 78 MM cases (60%) stain positive for CD99. This study is the first to demonstrate, in a large series, the prevalence of CD99 expression in primary cutaneous melanoma. Additionally, this introduces in the histologic differential diagnosis of CD99 expressing dermal spindle cell lesions.

P.219 Hyperbaric medicine. Our experience: results and applications

The peripheral primitive neuroectodermal tumor/Ewing's sarcoma family tumor (pPNET/ESFT) group includes small round cell tumors of the bone, soft tissue, and nerve with morphological attributes of the germinal neuroepithelium. Peripheral PNETs/ESFTs also occur within the craniospinal vault, a region including the central nervous system, the meninges, and the cranial and spinal nerve roots. Gene rearrangements between the EWS gene on chromosome 22q12 and members of the ETS gene family are common in and specific to pPNETs/ESFTs. Another defining characteristic of pPNETs/ESFTs is their membranous expression of the MIC2 gene product. We describe 2 cases of pPNETs within the craniospinal vault. An intradural tumor arising from the nerve roots of the cauda equina was discovered in a 32-year-old man presenting with radiculopathic back pain and lower-extremity weakness. An intracranial pPNET that mimicked a meningioma was found in a 21-year-old man presenting with headache and visual disturbances. MIC2 gene product expression and EWS/ETS gene rearrangement were detected in both case patients. The literature with regard to pPNETs/ESFTs arising within the craniospinal vault is reviewed.

Toxoplasma MIC2 Is a Major Determinant of Invasion and Virulence

Like its apicomplexan kin, the obligate intracellular protozoan Toxoplasma gondii actively invades mammalian cells and uses a unique form of gliding motility. The recent identification of several transmembrane adhesive complexes, potentially capable of gripping external receptors and the sub-membrane actinomyosin motor, suggests that the parasite has multiple options for host-cell recognition and invasion. To test whether the transmembrane adhesin MIC2, together with its partner protein M2AP, participates in a major invasion pathway, we utilized a conditional expression system to introduce an anhydrotetracycline-responsive mic2 construct, allowing us to then knockout the endogenous mic2 gene. Conditional suppression of MIC2 provided the first opportunity to directly determine the role of this protein in infection. Reduced MIC2 expression resulted in mistrafficking of M2AP, markedly defective host-cell attachment and invasion, the loss of helical gliding motility, and the inability to support lethal infection in a murine model of acute toxoplasmosis. Survival of mice infected with MIC2-deficient parasites correlated with lower parasite burden in infected tissues, an attenuated inflammatory immune response, and induction of long-term protective immunity. Our findings demonstrate that the MIC2 protein complex is a major virulence determinant for Toxoplasma infection and that MIC2-deficient parasites constitute an effective live-attenuated vaccine for experimental toxoplasmosis.

Decreased Immunoreactivity of CD99 Is an Independent Predictor of Regional Lymph Node Metastases in Pulmonary Carcinoid Tumors

Few data are available on the prevalence and clinicopathological meaning of CD99, the transmembrane product of the pseudoautosomal MIC2 gene, in pulmonary neuroendocrine tumors. We evaluated CD99 immunoreactivity in lung tissues, pulmonary neuroendocrine hyperplasias, and 136 consecutive pulmonary neuroendocrine tumors of diverse histological types. By immunohistochemistry, a membranous and/or cytoplasmic immunoreactivity was seen in 60 of 136 (44%) tumors, whereas both normal and hyperplastic neuroendocrine cells of the lung were consistently nonreactive. A steady decrease of the CD99 labeling index was observed from better to poorly differentiated tumors, with a prevalence of the membranous pattern in typical carcinoids (TCs), and of the cytoplasmic pattern in atypical carcinoids (ACs) and large cell neuroendocrine carcinoma/small cell lung carcinoma (P < 0.0001), independent of tumor stage. In TCs/ACs, increased levels of CD99 labeling index or the membranous pattern were associated with low proliferative fraction (P = 0.0011) and smaller tumor size (P = 0.0054) and with lack of regional lymph node metastases (P = 0.0078). Moreover, CD99 expression decreased according to the pN0-2 classes (P = 0.0016), with an inverse relationship between the number of positive lymph nodes, the labeling index (P = 0.013) and the nonmembranous pattern (P = 0.016). At multivariate analysis, both the decreased CD99 labeling index and the negative/cytoplasmic staining were independent risk indicators for lymph node metastases in the subset of TC/AC patients. No relevant relationships were found in large cell neuroendocrine carcinoma/small cell lung carcinoma. CD99 is especially present in low- to intermediate-grade neuroendocrine tumors of the lung, and loss of the marker correlates with the occurrence of nodal metastases in TC/AC patients.

Peripheral primitive neuroectodermal tumor/Ewing's sarcoma of the craniospinal vault: case reports and review

The peripheral primitive neuroectodermal tumor/Ewing's sarcoma family tumor (pPNET/ESFT) group includes small round cell tumors of the bone, soft tissue, and nerve with morphological attributes of the germinal neuroepithelium. Peripheral PNETs/ESFTs also occur within the craniospinal vault, a region including the central nervous system, the meninges, and the cranial and spinal nerve roots. Gene rearrangements between the EWS gene on chromosome 22q12 and members of the ETS gene family are common in and specific to pPNETs/ESFTs. Another defining characteristic of pPNETs/ESFTs is their membranous expression of the MIC2 gene product. We describe 2 cases of pPNETs within the craniospinal vault. An intradural tumor arising from the nerve roots of the cauda equina was discovered in a 32-year-old man presenting with radiculopathic back pain and lower-extremity weakness. An intracranial pPNET that mimicked a meningioma was found in a 21-year-old man presenting with headache and visual disturbances. MIC2 gene product expression and EWS/ETS gene rearrangement were detected in both case patients. The literature with regard to pPNETs/ESFTs arising within the craniospinal vault is reviewed.

Ewing's Sarcoma in the Spinal Nerve Root: A Case Report and Review of the Literature

Ewing's sarcoma (ES) is a highly malignant tumor composed of uniform small round cells. Recently, a single biologic entity, Ewing's sarcoma family of tumors (ESFT) has been accepted. The entity includes ES, extraskeletal Ewing's sarcoma (EES) and primitive neuroectodermal tumor (PNET). ESFT cells have immunoreactivity for CD99, an antigen determined by the MIC2 gene. Most ESFT has the (11;22) (q24;q12) translocation. The translocation results in the fusion of the EWS gene with the transcription factor gene FLI1 which has been considered a hallmark of ESFT. We present an extremely unusual case with ESFT in a spinal nerve root mimicking a neurogenic dumbbell tumor. A male aged 20 years noticed pain in his right buttock. Magnetic resonance imaging (MRI) revealed a mass in the right L5/S intervertebral foramen and the lesions in the sacrum. Surgery was performed with a presumptive diagnosis of a nerve sheath tumor. At surgery, the tumor was located in the right L5 nerve root sleeve. The sacral lesions were observed closely. At one month after surgery, radiologically multiple lesions were detected in the pelvic bones. Microscopically the lesions from the root and ilium were composed of small round cells immunoreactive for CD99. Reverse transcription-polymerase chain reaction detected transcripts resulting from the fusion of the EWS gene with FLI1 genes in the iliac lesion. Immunoreactivity for CD99 and detection of the EWS-FLI1 hybrid transcripts are important for the correct diagnosis of ESFT arising in an unusual location.

Rapid divergency of rodent CD99 orthologs: Implications for the evolution of the pseudoautosomal region

The human pseudoautosomal region 1 (PAR1) is essential for the obligatory X–Y crossover in male meiosis. Despite its critical role, comparative studies of human and mouse pseudoautosomal genes have been limited owing to the scarcity of genes conserved between the two species. Human CD99 is a 32-kDa cell surface protein that is encoded by the MIC2 gene localized to the PAR1. Although several sequences such as CD99L2, PBDX, and CD99L1 are related to CD99, its murine ortholog, Cd99, has not yet been identified. Here we report a novel mouse Cd99, designated D4, which shows overall sequence homology to CD99, with the highest conservation between the two genes being found in the transmembrane regions. In addition, the D4 protein displays biochemical characteristics, functional homology, and expression patterns similar to those of CD99. The D4 gene is localized on an autosome, chromosome 4, reflecting a common mapping feature with other mouse orthologs of human PAR1 genes. Furthermore, a phylogenetic analysis of CD99-related genes confirmed that the D4 gene is indeed an ortholog of CD99 and exhibits the accelerated evolution pattern of CD99 orthologs, as compared to the CD99L2 orthologs. On the basis of these findings, we suggest that CD99 belongs to the ancient PAR genes, and that the rapid interspecies divergence of its present sequence and map position is due to a high recombination frequency and the occurrence of chromosomal translocation, supporting the addition–attrition hypothesis for PAR evolution.

Peripheral primitive neuroectodermal tumor of the cerebellopontine angle

Peripheral primitive neuroectodermal tumors are highly malignant small cell neoplasms. A 27-year-old female presented with a 6-month history of right-sided facial pain and progressive weakness of the facial muscles. She had non-pulsative tinnitus, progressive right hearing loss and facial palsy. T2-weighted MRI showed a heterogeneous hyperintense lesion invading the right internal auditory canal. Surgical removal was performed. Pathological examination showed sheets of small cells with irregular nuclei. Immunohistochemical studies demonstrated positive immunoreactivity for neuron-specific enolase, synaptophysin, chromogranin, vimentin, S-100 protein and p30-32 MIC-2 gene product. The patient was treated with chemotherapy (etoposide, vincristine, adriamycin, ifosfamide and actinomycin D) and radiotherapy. After 65 months of follow-up, the patient presented with cervical metastasis. Radical cervical dissection was performed and the patient was treated with a second course of chemotherapy. At control MRI after 29 months of follow-up the patient showed no signs of local recurrence or distant metastasis.

Primitive Neuroectodermal Tumor of the Uterus: A Case Report

Primitive neuroectodermal tumors (PNETs) are a group of unusual malignancies arising in the bone and soft tissue. Pure uterine neuroectodermal tumors are rare. We report the first case of PNET arising from the uterus in our hospital. A 52-year-old perimenopausal woman had multiple myoma and was regularly followed-up in our hospital. She suddenly developed lower abdominal pain without vaginal bleeding. Sonography revealed a pelvic mass measuring 10.7 × 6.8 cm with multiple myoma. The patient underwent tumor resection. There were multiple necrotic tumors on the uterus, bladder, broad ligaments, cardinal ligaments, and cul-de-sac. Final pathology revealed PNET because tumor cells were CD99 positive. PNETs belong to the Ewing's sarcoma family. They are closely related to malignant, small round-cell tumors of soft tissue and bones. They strongly express the glycoprotein p30/32 (CD99) on the cell membrane, which is encoded by the MIC2 gene. A translocation at t(11;22)(q24;q12) has been identified. PNETs are mostly recognized by the histologic characteristics of neural differentiation and immunohistochemical expression of at least two different neural markers. Uterine PNETs have a poor prognosis and, to date, there is no standard treatment. Total abdominal hysterectomy and bilateral salpingo-oophorectomy plus adjuvant chemotherapy or radiotherapy are recommended.