[Clinicopathological characteristics of gastric SMARCA4-deficient undifferentiated/rhabdoid carcinoma].

Objective: To investigate the clinicopathological features and immunohistochemical phenotypes of gastric SMARCA4-deficient undifferentiated carcinoma, and to discuss the daily diagnostics of this entity and analyze its prognosis. Methods: The cases of gastric SMARCA4-deficient undifferentiated carcinoma diagnosed at the Department of Pathology, Peking University Cancer Hospital, China from January 2010 to August 2022 were collected. The histological sections were reviewed, the immunohistochemical results and clinicopathological features were analyzed, and relevant literature was reviewed. Results: Pure foci of undifferentiated carcinoma were seen in 7 cases, and 1 case was accompanied by a moderately differentiated tubular adenocarcinoma component. Undifferentiated carcinoma foci showed similar sheet-like or solid diffuse growth pattern, medium-sized tumor cells characterized by 1-2 nucleoli, and abundant cytoplasm and rhabdoid appearance. The average patient age was 65±8 years. Six patients were male and 2 were female. Immunohistochemical staining showed that undifferentiated carcinoma of all 8 tumors were negative for SMARCA4 (BRG1). Among 7 patients who underwent SMARCA2 (BRM) and SMARCB1 (INI1) staining, 4 cases showed loss of BRM expression, 2 cases showed weakly positive staining, and 1 case was diffusely positive, but all 7 cases were diffusely strong positive for INI1. The neuroendocrine marker, synaptophysin, was weakly positive in 5 cases, while CgA and CD56 were negative in 8 cases. Ki-67 index was more than 70%. Two cases were mismatch repair deficient and showed the loss of MLH1/PMS2 expression, while 1 case showed only MSH2 loss. PD-L1 staining showed that combined positive score (CPS)≥1 in 4 cases (CPS ranging from 1 to 55) and CPS<1 in the other 3 cases. Four patients had clinical stage Ⅳ disease. Two of them died within 3 months after diagnosis. Conclusions: Gastric SMARCA4-deficient undifferentiated carcinoma/rhabdoid carcinoma is a rare group of highly malignant tumors with a poor prognosis. Loss of the core subunit of SWI/SNF complex may be associated with the development of dedifferentiated histological pattern and aggressive tumor progression, which may be more frequently accompanied with mismatch repair deficiency.目的： 探究胃SMARCA4缺失型未分化癌/横纹肌样癌的临床病理特征、免疫表型，探讨此类疾病日常诊断要点及分析预后。 方法： 收集北京大学肿瘤医院病理科2010年1月至2022年8月确诊的胃SMARCA4缺失型未分化癌/横纹肌样癌病例，复阅HE切片，分析免疫组织化学结果，记录临床病理学信息，并复习相关文献。 结果： 共计检索出相关病例8例。其中包括根治标本3例，活检标本5例。患者平均发病年龄（65±8）岁，男性6例，女性2例。镜下组织学形态表现：7例仅见未分化癌区域，1例伴有中分化管状腺癌成分，8例未分化区域均呈实性弥漫性生长方式，肿瘤细胞中-重度异型，可见1~2个核仁，胞质较丰富、上皮样，细胞边界不清，部分病例伴有明显横纹肌样细胞分化，细胞黏附性较差。免疫组织化学染色结果显示，8例未分化癌均表现为SMARCA4（BRG1）染色阴性，7例进行SMARCA2（BRM）及SMARCB1（INI1）染色病例中，4例BRM表达缺失，2例呈弱阳性，1例弥漫阳性，7例INI1均为弥漫强阳性。少部分患者上皮性标志物广谱细胞角蛋白（CKpan）及上皮细胞膜抗原（EMA）呈阴性或弱阳性表达。5例神经内分泌标志物突触素呈弱阳性表达，而嗜铬粒素A（CgA）及CD56在8例患者中均为阴性。Ki-67阳性指数均>70%。2例标本为错配修复蛋白缺陷，表现为MLH1/PMS2表达缺失，另有1例仅出现MSH2表达缺失，余病例均为错配修复蛋白完整。PD-L1染色结果为4例患者综合阳性评分（CPS）≥1（CPS范围1~55），另3例患者CPS<1。4例患者在就诊时发现同期转移，为临床Ⅳ期患者，其中2例患者于确诊后3个月内死亡，中位随访时间为10个月。 结论： 胃SMARCA4缺失型未分化癌为一组罕见发病、高度恶性的肿瘤，预后较差。SWI/SNF复合物核心亚基缺失可能与其发生去分化组织学形态以及高度侵袭性相关，并更常伴有错配修复蛋白缺陷。.