SMARCB1/INI1 Deficient Sino-Nasal Carcinoma: Extending the Histomorphological Features

Abstract

SMARCB1/INI1 deficient sinonasal carcinoma is a variant of sinonasal undifferentiated carcinoma (SNUC). There is a paucity of literature describing the histomorphological features of this relatively new entity. Herein we describe the histomorphological features of three such cases and review the literature. We retrospectively reviewed the cases of SNUC diagnosed in our institute in the last 6 years. Immunohistochemistry for INI1, NUT & p16 were performed on these cases. Three cases showed loss of INI1. The histomorphology and clinicopathological features of these cases were studied and compared with non INI1 deficient SNUC. A total of 9 cases of SNUC were identified. Three of these cases showed loss of INI1. These three cases had presented with large sinonasal mass and with intracranial extension. Histopathology of these cases showed a diffuse infiltrative pattern, nest, and islands of predominantly basaloid cells with focal rhabdoid morphology. Additional features like small cell carcinoma like pattern, pseudoalveolar and pseudoglandular patterns, clear vacuoles and pseudopapillary appearance were also noted. We conclude that in presence of a mixed pattern of cells with a predominance of basaloid morphology, the possibility of SMARCB1/INI1 deficient sinonasal carcinoma must be strongly suspected and immunohistochemistry for INI1 must be performed.

Keywords: Basaloid morphology; Rhabdoid morphology; SMARCB1/INI1 deficient sinonasal carcinoma; Sinonasal undifferentiated carcinoma; p16.

Fig. 1

The histomorphology of SNUC cases showing a infiltrative nests and islands (Hematoxylin and Eosin, 200 ×), b small cell morphology with crushing artefact and moulding of tumor cells (Hematoxylin and Eosin, 100 ×), c single or small discohesive clusters of tumor cells with pericellular halo resembling a high grade Non Hodgkin Lymphoma, (Hematoxylin and Eosin, 200 ×), d sarcomatoid morphology (Hematoxylin and Eosin, 200 ×), and e Rhabdoid morphology in a case, (Hematoxylin and Eosin, 400 ×), f The rhabdoid cells were immunopositive for INI1 (Immunostain, 400x)

Fig. 2

Immunohistochemical profile of Sinonasal Undifferentiated carcinoma, a Pan-Ck, focal weak expression/loss was seen in one case, immunostain 200 ×. b Focal weak expression of EMA was noted in some cases, immunostain 200 ×. c Focal expression of synaptophysin is seen in some cases, immunostain 200 ×. d Diffuse membranous expression of CD99 was seen in one case, immunostain 200 ×. e Paranuclear dot like positivity of CD99 seen in one case, immunostain 200x, f Tumor cells showed membranous positivity for beta catenin. Immunostain 200 ×

Fig. 3

The histomorphology of case 1-SMARCB1/INI1 deficient sinonasal carcinoma showing a diffuse infiltrative nests and cords (Hematoxylin and Eosin, 100 ×), b small cell carcinoma like pattern (Hematoxylin and Eosin, 200 ×), c intimate admixture of two population of cells; cells with moderate amount of cytoplasm, round vesicular nucleus and prominent nucleoli and basaloid cells (Hematoxylin and Eosin, 400 ×), d, e infiltration of islands of tumor cells in bone, there is marked fibroblastic proliferation and new bone formation giving rise to a fibrous dysplasia like reaction, (Hematoxylin & Eosin, 100x), f Complete loss of INI1 protein in the tumor cells with positive internal control (immunostain, 400 ×)

Fig. 4

The histomorphology of case 2-SMARCB1/INI1 deficient sinonasal carcinoma showing a diffuse sheets of tumor cells with geographic areas on necrosis. (Hematoxylin and Eosin,  40 ×), b, c perivascular arrangement of tumor cells (Hematoxylin and Eosin, 200 ×), d, e The tumor cells were small to intermediate sized with high N/C ratio, vesicular chromatin, and prominent nucleoli (Hematoxylin and Eosin, 400 ×), f Complete loss of INI1 protein in tumor cells with positive internal control (immunostain, 400 ×)

Fig. 5

The histomorphology of case 3-SMARCB1/INI1 deficient sinonasal carcinoma showing a, b nests and lobules of tumor cells (Hematoxylin and Eosin, 400 ×, c pseudoglandular pattern containing empty vacuoles, (Hematoxylin and Eosin, 400 ×) d pseudoalveolar pattern (Hematoxylin and Eosin,  400 ×), e lobules of tumor cells with rhabdoid morphology of cells (Hematoxylin and Eosin, 200 ×), f Complete loss of INI1 protein with positive internal control (immunostain, 200 ×)