SMARCA4-deficient sarcoma of thorax

SMARCA4-deficient sarcoma of the thorax (also known as SMARCA4-deficient thoracic sarcoma, or SMARCA4-DTS) is an extremely rare and highly aggressive malignant tumor that arises in the thoracic region, most commonly in the mediastinum, lung, or pleura. This cancer is characterized by the loss of expression of the SMARCA4 protein (also called BRG1), which is a critical component of the SWI/SNF chromatin remodeling complex involved in regulating gene expression. The tumor predominantly affects young to middle-aged adult males, often with a history of heavy smoking. It was previously sometimes confused with other thoracic malignancies, including SMARCA4-deficient non-small cell lung carcinoma, but is now recognized as a distinct entity. Clinically, patients typically present with a rapidly growing thoracic mass that may cause chest pain, cough, dyspnea (shortness of breath), and symptoms related to compression or invasion of surrounding structures such as the great vessels, airways, and chest wall. The tumor tends to be large at diagnosis and frequently shows aggressive local invasion and distant metastases. Histologically, it is composed of sheets of relatively uniform, round to epithelioid cells with rhabdoid features and demonstrates complete loss of SMARCA4 (BRG1) expression by immunohistochemistry, often accompanied by loss of SMARCA2 (BRM) expression. The prognosis for SMARCA4-deficient thoracic sarcoma is generally very poor, with most patients surviving less than one year from diagnosis. Treatment options remain limited and there is no established standard therapy. Multimodal approaches including surgery (when feasible), platinum-based chemotherapy, and radiation therapy have been attempted with limited success. Immune checkpoint inhibitors (such as anti-PD-1/PD-L1 agents) have shown some responses in individual cases and are being explored as potential therapeutic options. Clinical trials investigating novel targeted therapies, including EZH2 inhibitors, are also under investigation given the underlying epigenetic dysregulation.

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