Abstract
BACKGROUND: SMARCA4-deficient undifferentiated tumor (SMARCA4-UT) is a rare and highly malignant primary tumor characterized by the loss of SMARCA4 expression. Despite advancements in oncology, diagnosing and treating SMARCA4-UT remain significant clinical challenges. CASE DEMONSTRATION: A 67-year-old male with a history of smoking presented to the hospital with complaints of abdominal distention and pain lasting for more than four days. Abdominal computed tomography (CT) revealed a high-density mass measuring approximately 41 × 37 mm in the right lower quadrant. Additionally, chest CT identified a high-density mass measuring 63 × 48 mm in the upper lobe of the right lung. The patient underwent partial small bowel resection, and postoperative pathological examination confirmed a diagnosis of SMARCA4-UT originating in the small mesentery. Unfortunately, the patient succumbed to respiratory failure 21 days after the diagnosis. CONCLUSION: SMARCA4-UT is an exceedingly rare and aggressive undifferentiated tumor. This case highlights a presentation of SMARCA4-UT with abdominal pain and distention as initial symptoms. Clinicians should consider SMARCA4-UT in middle-aged or elderly male patients with a history of smoking who present with large masses. Comprehensive chest imaging is essential to exclude the thoracic primary disease in such cases.