胸膜SMARCA4缺失未分化肿瘤是一种罕见的发生于胸膜的未分化肿瘤，其形态学特征为细胞分化差，组织学及免疫组织化学染色证实其缺乏腺性、鳞状或其他明显细胞谱系特征，而以浆细胞样、横纹肌母细胞样细胞形态和SMARCA4表达缺失为特征。本文报道的该例胸腔SMARCA4缺失未分化肿瘤患者，肿瘤细胞呈浆细胞样或横纹肌母细胞样，细胞分化差，免疫组化染色提示肿瘤细胞Syn阳性，SMARCA4表达缺失，Ki-67增殖指数为80%，其余标记均为阴性。该患者吸烟，既往体健，起病隐匿，发现时已为晚期，术后未经过放化疗等任何干预措施，生存期仅66 d，与文献报道术后接受常规治疗的晚期患者相比，生存期并无明显差异。笔者回顾分析其临床资料、组织形态学及免疫组化特征，并复习相关文献，提示SMARCA4缺失性未分化肿瘤具有高度侵袭性，预后差。

Thoracic SMARCA4-deficient undifferentiated tumor is a rare type of undifferentiated tumor occurring in the pleura. Their morphological features are poorly differentiated. A malignant tumor that lacks glandular, squamous, or other distinct cell lineages, as demonstrated by histological and immunohistochemical staining, is characterized by plasmacytoid and rhabdomytoid cell morphology and loss of SMARCA4 expression. We report a case of an undifferentiated tumor in the pleura with a SMARCA4 deletion,The tumor cells were plasmacytoid or rhabdomytoid，Poor cell differentiation, Immunohistochemical staining showed Syn positive in tumor cells,SMARCA4 expression is deficient,The proliferation index of Ki-67 was 80%,Other markers were all negative The patient was a heavy smoker and previously healthy.Patients with insidious onset,It was found in an advanced stage.After the surgery, no treatment was administered, and the patient survived for only 66 days.There was no significant difference in the survival time of advanced patients who received traditional treatment after surgery compared with those reported in the literature.The clinical data, histological characteristics and immunohistochemistry were retrospectively analyzed, and a review of the relevant literature suggests that SMARCA4-deficient undifferentiated tumors are highly aggressive and have a poor prognosis.