Thoracic SMARCA4-deficient undifferentiated tumor

Abstract

Thoracic SMARCA4-deficient undifferentiated tumor (SMARCA4-UT) is characterized by an undifferentiated rhabdoid morphology and SMARCA4 deficiency pathologically. In the 2021 revision of the WHO classification, it was categorized as an epithelial tumor because of its shared genetic background with smoking-related lung cancer. We describe the case of a 44-year-old man with a rapidly enlarging mediastinal mass observed on chest radiography and CT. The tumor was resistant to radiation therapy, chemotherapy, and immune checkpoint inhibitors, and the patient's survival time was approximately 5 months. Familiarity with the clinical background and imaging findings of thoracic SMARCA4-UT is crucial for early diagnosis and treatment planning.

Keywords: CT; Heavy smokers; Mediastinal mass; SMARCA4-deficient undifferentiated tumor.

Fig. 1

(A and B) Noncontrast CT (2 weeks before admission), axial slices. A tumor measuring 5.0 × 5.0 cm was observed in the superior-to-anterior mediastinum.

Fig. 2

Chest radiography at admission showed an enlarged shadow in the right upper mediastinum.

Fig. 3

(A-E) Dynamic CT axial and coronal images at admission. The tumor showed poor contrast enhancement, with gradual enhancement during the equilibrium phase. It had grown to 9.0 × 7.0 cm within 2 weeks, compressing the right brachiocephalic vein and superior vena cava (A, C, E). Enlarged metastatic lymph nodes were observed around the right pulmonary hilum and trachea (B, D).

Fig. 4

(A-D) HE staining revealed pleomorphic cells with prominent nucleoli and large nuclei proliferating in clusters, with extensive necrosis, apoptosis, and mitotic figures (A). Immunohistochemistry showed EMA positivity (B), weak AE1/AE3 positivity (C), and SMARCA4 negativity (D).

Fig. 5

(A-D) Head MRI shows T2WI (A), T1WI (B), and Gd-FS T1WI axial (C) and sagittal (D) images. A mass with low signal on T1WI, high signal on T2WI, and poor contrast enhancement is observed in the cortical to subcortical region of the right parietal lobe, indicating a brain metastasis with prominent internal necrosis.

Fig. 6

(A-D) Contrast-enhanced CT axial images on day 107 of hospitalization. The mediastinal tumor increased in size, measuring 11 × 8 cm (A). Metastases were observed in the right supraclavicular lymph nodes (B), multiple hepatic lesions (C), and upper abdominal lymph nodes (D).