SMARCB1/INI1-deficient undifferentiated tumour of the thorax: a case report and review of the literature

Abstract

The 5th WHO classification of thoracic tumours includes thoracic SMARCA4-deficient undifferentiated tumour (SMARCA4-UT) among the "other epithelial tumours of the lung" chapter. Herein, we present a case of undifferentiated thoracic neoplasm with retention of SMARCA4 expression, lack of NUT fusion protein and loss of SMARCB1/INI1 expression. After presenting the clinical and pathological features of the tumour, we carried out a review of the literature on the same topic. Albeit very rare, we believe this entity should be included in the heterogeneous group of undifferentiated neoplasms of the thorax.

Keywords: SMARCA4-deficient undifferentiated tumour; SMARCB1-deficient undifferentiated tumour; SWI/SNF complex; thoracic undifferentiated tumours.

Figure 1.

CT image of the reported case. Thoracic computed tomography at initial diagnosis. The image shows a grossly rounded, solid formation located peripherically in the right middle lobe of the lung.

Figure 2.

Histopathological and immunohistochemical features of the tumour. Haematoxylin and eosin staining of the lesion showed a solid proliferation of small, round, undifferentiated cells with focal necrosis, occasional cytoplasmic vacuolisation and perivascular palisading (a). Neoplastic cells stained positive for p40 (50% of the neoplastic cells) and negative for TTF-1 and synaptophysin (b, c, d). Immunohistochemical study of the expression of SMARCA4/BRG1 (e) and SMARCB1/INI1 (f) demonstrated the retention of the former and the complete loss of staining, with positive internal control, of the latter.