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Title: [Clinicopathological characteristics of myxoid solitary fibrous tumor: analysis of seven cases].
Author: Cai JJ, He XL, Zhao M.
Journal: Zhonghua Bing Li Xue Za Zhi; 2020 Sep 08; 49(9):910-915. PubMed ID: 32892556.
Abstract:
Objective: To investigate the clinicopathological characteristics, immunophenotypes, and diagnostic and differential diagnostic features of myxoid solitary fibrous tumor (SFT). Methods: Seven cases of myxoid SFT were collected from the archives of Zhejiang Provincial People's Hospital from January 2014 to December 2019. The clinical features, histomorphology, immunohistochemistry, molecular genetics and prognosis were analyzed and the relevant literature was reviewed. Results: There were three male and four female patients ranging from 32 to 67 years. Locations included the pleura (three cases), pelvic cavity, vagina, parotid gland, and nasal cavity(one each). Tumor size ranged from 2.7 to 13.5 cm. Histologically, all cases were characterized predominantly by the presence of myxoid stroma comprising 55% to 90% of the tumor (mean 72%). The tumors were composed of predominantly stellated, spindled or ovoid cells disposed haphazardly, in loose fascicles, or in anastomosing strands imparting a microcystic/reticular appearance in a extensively myxoid, richly vascularized stroma. Staghorn-shaped branching vessels and thin strands of collagen were commonly seen between tumors cells amidst the myxoid background. These myxoid areas were punctuated by small cellular areas showing diagnostic features of classical SFT, which were present in all seven cases. Areas showing giant cell angifibroma-like change were noted in 2 cases and focal lipomatous metaplasia was identified in 1 case. Atypical features suggestive of aggressive behavior were present in 2 cases and in one of the cases myxoid SFT with high-grade sarcomatous overgrowth was noted. Immunohistochemically, tumor cells in all cases stained positively for STAT6 and CD34. Polymerase chain reaction technique showed in both the examined cases the characteristic NAB2ex4-STAT6ex2 fusion gene. According to the Demicco's risk assessment model, four cases were classfied as low, one was classified as moderate and 2 was classified as high. Follow-up information was obtained in 4 cases. One tumor recurred 3 times within 48 months after operation, and the other 3 cases had no tumor recurrence and metastasis. Conclusions: Myxoid SFT represents a rare morphologic variant of SFT with biological behaviors ranging from indolent to aggressive. Myxoid SFT should be included in the differential diagnostic spectrums of soft tissue tumors with significantly myxoid change. Carefully searching for the typical SFT histomorphology with the use of immunohistochemistry and if necessary, molecularly testing for NAB2-STAT6 fusion can help to distinguish myxoid SFT from its many mimickers. 目的： 探讨黏液型孤立性纤维性肿瘤（SFT）的临床病理特征、免疫表型、分子遗传学特点以及鉴别诊断要点。 方法： 收集2014年1月至2019年12月间就诊于浙江省人民医院的7例黏液型SFT患者资料，总结其临床特征、组织形态学、免疫表型、分子遗传学特征以及预后，并结合相关文献进行复习。 结果： 男性3例，女性4例。发病年龄32~67岁。发病部位：胸膜3例，盆腔、阴道、腮腺和鼻腔各1例。瘤体直径2.7~13.5 cm。镜下，黏液变性区占肿瘤的55%~90%（平均约72%），瘤细胞星芒状、短梭形或卵圆形，呈疏松的束状、交织带状和微囊/网状分布于富于血管的广泛黏液变的基质之中。常见鹿角形分支状血管，瘤细胞之间常见薄的胶原纤维沉积。所有病例中均可见黏液性背景中散在的经典型SFT结构。2例可见局灶的巨细胞血管纤维瘤样结构，1例可见局灶的脂肪化生。2例可见提示侵袭性生物学行为的组织学特征，其中1例显示黏液型SFT伴高级别肉瘤性过渡生长。免疫组织化学染色所有肿瘤（7/7）均弥漫表达STAT6和CD34。对2例肿瘤行PCR检测提示均存在NAB2基因的第4号外显子和STAT6基因的第2号外显子融合。根据Demicco提出的SFT危险度分级模式，4例为低度危险，1例中度危险，2例高度危险。4例获得随访信息，1例肿瘤在术后4年内复发3次，另3例未见肿瘤复发和转移。 结论： 黏液型SFT是一种罕见的SFT组织学亚型，生物学行为可从惰性到侵袭性。黏液型SFT应包括在具有显著黏液变性的软组织肿瘤的鉴别诊断谱系之中，仔细的组织学观察寻找典型的SFT组织学特征并辅以免疫组织化学染色和必要的分子遗传学检测可助于其诊断和鉴别诊断。.

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