Primary SMARCA4-deficient undifferentiated sarcomatoid tumor of the gastroesophageal junction

Background

SMARCA4-deficient thoracic sarcoma (SDTS) is a recently described high grade malignancy which occurs exclusively in the thoracic cavity. Extra-thoracic involvement has been rarely described.

Case presentation

We describe here a unique case of SMARCA4-deficient undifferentiated sarcomatoid tumor (SDUST) arising primarily in the gastroesophageal junction of a 40-year-old female who is a never smoker. Histologically, the lesion showed a composite tumor composed of an undifferentiated round cell tumor and a well-differentiated spindle cell tumor, which was initially interpreted as a poorly differentiated neuroendocrine carcinoma (NEC) combined with a gastrointestinal stromal tumor (GIST) respectively. However, a comprehensive reevaluation of the submitted slides demonstrated an undifferentiated sarcomatoid tumor with striking rhabdoid morphology combined with a benign leiomyoma. Immunohistochemically, the undifferentiated sarcomatoid tumor showed a complete loss of SMARCA4 and SMARCA2, negativity for claudin-4, overexpression of SOX2, strong and diffuse expression of CD34, consistent with the phenotype of SDUST. By next-generation sequencing (NGS) analysis, tumor cells harbored TP53 gene mutation.

Conclusion

This case demonstrates that SDUST may also develop in the gastrointestinal tract. Recognizing this distinct entity is important for both prognostic and therapeutic considerations.