读片会简介：上海市骨软组织病理读片会由上海肿瘤医院王坚教授和朱雄增教授提议创建于2007年。每季度举行一次， 每次讨论12例左右精彩的骨软组织疑难和罕见病例。2010年第一次读片会（2010-3-6）在上海瑞金医院举行，讨论的病例包括：

1）腹腔促纤维增生性小圆细胞肿瘤；

2）不典型纤维组织细胞瘤；

3）右心室转移性子宫平滑肌瘤；

4）神经纤维瘤病恶性变；

5）儿童多形性未分化肉瘤；

6）肾小球样血管瘤（POEMS综合症）

7）恶性颗粒细胞瘤；

8）男性会阴深部侵袭性血管粘液瘤；

9）乳腺癌放疗后不典型血管病变；

10）阴茎根部上皮样肉瘤；

11）食管肌层炎性肌纤维母细胞样肿瘤；

12）股骨颈软骨肉瘤3级，形态酷似软骨粘液样纤维瘤；

13）十二指肠-胰头部肿瘤（上海中山医院病理科-纪元教授提供）

现将上海中山医院病理科纪元教授提供的一例非常精彩的“十二指肠-胰头部肿瘤”提供大家欣赏。

男31岁，梗阻性黄疸2周。腹部CT示十二指肠降部占位。临床诊断：十二指肠间质瘤，行保留幽门十二指肠切除术。 手术中见肿瘤位于胰头和十二指肠降部，大小5x4cm，局部浸润横结肠系膜。

 MiTF+， HMB-45+， Melan A +。

 MiTF+， HMB-45+， Melan A +。

上海中山医院病理科是研究GIST很著名的单位。她们做了全部GIST的标价和DNA测序，结果均阴性，结合HE形态，除外了GIST。
最后诊断聚焦在恶性PEComa和恶性黑色素瘤上。请大家就这二者的诊断和鉴别继续发表意见，谢谢！

 MiTF+， HMB-45+， Melan A +。IHC 标记结果：CD117-、SMA-、desmin-

1. Joo M, Chang SH, Kim H, Gardner JM, Ro JY.

Primary gastrointestinal clear cell sarcoma: report of 2 cases, one case associated with IgG4-related sclerosing disease, and review of literature. Ann Diagn Pathol. 2009;13:30-5.

Department of Pathology, Inje University Ilsan Paik Hospital, Goyang, South Korea.

Clear cell sarcoma (CCS) is a distinctive soft tissue sarcoma that shows melanocytic differentiation. Primary gastrointestinal (GI) CCSs have been rarely reported, but to our knowledge, no association between GI CCSs and immunoglobulin G4 (IgG4)-related sclerosing disease has been described in the literature. We experienced 2 cases of CCS that arose in the small intestine and metastasized to the liver. Histologic features and immunophenotype were typical of CCS. One of them showed a unique peritumoral sclerosing inflammatory reaction, which was highly reminiscent of IgG4-related sclerosing inflammatory disease. Dense lymphoplasmacytic infiltration with extensive sclerosis and obliterative phlebitis was observed in the immediate vicinity of the primary and metastatic tumors, but not in the distant areas from the tumor. The average number of IgG4-positive plasma cells was more than 50 per high-power field. We report 2 cases of primary GI CCS with one case showing a unique peritumoral IgG4-related lymphoplasmacytic sclerosing inflammation.

2.Lyle PL, Amato CM, Fitzpatrick JE, Robinson WA. Gastrointestinal melanoma or clear cell sarcoma? Molecular evaluation of 7 cases previously diagnosed as malignant melanoma. Am J Surg Pathol. 2008;32:858-66.

Clear cell sarcoma (CCS) is a rare tumor classically associated with the tendons and aponeuroses of distal extremities of young adults. CCS and malignant melanoma (MM) share immunohistochemical profiles and ultrastructural features, but classic CCS has characteristic morphology with low mitotic activity and minimal pleomorphism. Occasional cases show pleomorphism, high mitotic index, and/or melanin pigmentation, making CCS indistinguishable from MM based on morphology. However, CCS is genetically distinct owing to its consistent association with a t(12;22)(q13;q12) chromosomal translocation, leading to the formation of the EWS/ATF1 fusion transcript. This translocation has never been documented in cutaneous melanoma, and thus is regarded as specific for CCS. Recent evidence suggests that primary "malignant melanomas" in unusual anatomic sites, most notably the gastrointestinal (GI) tract, may be CCS. This is supported by 11 cases of primary GI CCS with the t(12;22) translocation. We used RT-PCR and FISH to examine whether a proportion of cases diagnosed as MM of the GI tract in patients without a history of cutaneous MM actually represent primary GI CCS. In total, we examined 7 cases: Four with no prior history of MM, 2 with histories of cutaneous MM, and 1 with an anal MM. All 4 cases for which there was no history of cutaneous/mucosal MM harbored the EWS/ATF1 fusion transcript. We report the largest series of GI CCS and have shown that molecular studies may be warranted in cases that otherwise seem to represent MM of unusual primary locations.

3. Dow N, Giblen G, Sobin LH, Miettinen M. Gastrointestinal stromal tumors: differential diagnosis. Semin Diagn Pathol. 2006;23:111-9.

Division of Gastrointestinal Pathology, Armed Forces Institute of Pathology,Washington, DC 20306-6000, USA. down@afip.osd.mil

Availability of KIT tyrosine kinase inhibitors for specific treatment of GISTs has magnified the importance of accurate differential diagnosis of GIST from other tumors occurring in the GI tract and abdomen. The general problems in this distinction include histological mimicry of other mesenchymal tumors with GIST,occasional KIT-negativity of GIST, and KIT-positivity of non-GISTs. Up to 5% to 10% gastric GISTs and <2% of intestinal GISTs can be KIT-negative. The identification of these tumors as GISTs is based on knowledge of the spectrum of GIST morphology, and can be supported by molecular diagnosis of KIT and PDGFRA mutations (the latter pertain to gastric tumors).

True smooth muscle tumors (rare in GI tract except in esophagus and colon) can be separated from GISTs by the eosinophilic tinctorial quality of tumor cells, positivity for smooth muscle markers, and negativity for KIT.

Desmoids can form large GIST-like masses, but are composed of spindled or stellate-shaped cells in a densely collagenous stroma. Negativity for KIT and nuclear positivity for beta-catenin are differentiating features. GI schwannomas, melanoma, and rare primary clear cell sarcoma are S100-positive, usually with characteristic histology. The latter two can be KIT-positive. KIT-

positive non-GISTs include some sarcomas, especially angiosarcoma and Ewing sarcoma, extramedullary myeloid tumor, seminoma, and a few carcinomas, notably small cell carcinoma of lung. Spurious KIT-positivity, seen with some polyclonal KIT antibodies, has been a source of confusion leading to probable false-positive results in fibroblastic tumors and occasional other sarcomas, such as leiomyosarcomas. Integration of histological features with carefully standardizedimmunohistochemistry, supported by KIT and PDGFRA mutation analysis, is the cornerstone of state-of-the art differential diagnosis of GIST. To comprehensively capture all GISTs, KIT immunostains should be performed on all unclassified epithelioid and mesenchymal tumors of the abdomen. This is a US government work. There are no restrictions on its use.

4. Agaimy A, Wünsch PH.Perivascular epithelioid cell sarcoma (malignant PEComa) of the ileum. Pathol Res Pract. 2006;202:37-41.

Institut für Pathologie, Klinikum Nürnberg, Prof. Ernst-Nathan-Strasse 1, 90419

Nürnberg, Germany. abbas.agaimy@klinikum-nuernberg.de

Epithelioid angiomyolipoma (AML) is the prototype of a heterogeneous group of lesions characterized by the presence of HMB-45 positive cells with clear cytoplasm, perivascular distribution, and combined myomelanocytic features,so-called perivascular epithelioid cells (PECs). These lesions are being increasingly referred to as PEComas. PEComas have been reported at diverse anatomic sites, but mainly in the abdominopelvic cavity and rarely in parenchymatous organs, skin, and soft tissues. Gastrointestinal (GI) PEComas are exceptionally rare, with less than 10 cases documented so far. Rare examples of PEComas with pleomorphic histology could have been misinterpreted as unusual variants of carcinoma or sarcoma. To make a contribution to the differential diagnosis of difficult-to-classify pleomorphic GI sarcomas, we report on a malignant pleomorphic neoplasm with features of PEComa involving the terminal ileum in a 63-year-old woman. Fourteen months after resection of the primary tumor, a huge abdominopelvic recurrence was successfully resected, but no distant metastases were detected. The differential diagnosis and malignancy criteria of GI PEComas will be discussed.

5. Covinsky M, Gong S, Rajaram V, Perry A, Pfeifer J. EWS-ATF1 fusion transcripts in gastrointestinal tumors previously diagnosed as malignant melanoma. Hum Pathol. 2005;36:74-81.

BACKGROUND: Clear cell sarcoma (CCS) is classically a deep soft tissue tumor associated with tendons or aponeuroses, although cases of primary CCS of the gastrointestinal (GI) tract have recently been reported. Because it is difficult to distinguish CCS from metastatic melanoma based on morphology, immunohistochemical profile, and ultrastructural features, it is possible that some GI tumors diagnosed as metastatic melanoma actually represent primary GI CCS. Because the EWS-ATF1 fusion transcript and the associated t(12;22)(q13;q12) translocation occur in CCS but not cutaneous melanoma, we investigated the use of molecular-based testing for discriminating CCS from metastatic melanoma (MM) in GI tumors.

METHODS: Patients with GI tumors diagnosed as MM were identified from departmental files. The tumors were tested for EWS-ATF1 fusion transcript by RT-PCR and fort(12;22)(q13;q12) by fluorescence in situ hybridization. RESULTS: Detailed review of medical records revealed that 16 (80%) of the 20 had a documented history of cutaneous melanoma. Two cases (10%) harbored the EWS-ATF1 fusion transcript, and fluorescence in situ hybridization confirmed the presence of t(12;22) in both cases. Of the 2 positive tumors, 1 developed in a patient who had no history of cutaneous melanoma, and the other developed in a patient with a remote history of vulvar melanoma.CONCLUSION: Based on molecular genetic findings, a subset of GI tumors diagnosed as MM by routine histopathologic evaluation represents CCS.