Cytopathologic features of SMARCB1 (INI-1)-deficient sinonasal carcinoma

BACKGROUND: SMARCB1 (INI-1)-deficient sinonasal carcinoma (IDSNC) is a newly described, poorly differentiated carcinoma. Herein, the authors describe the cytopathologic features of IDSNC in fine-needle aspiration (FNA) samples. METHODS: The pathology archives of 2 academic institutions were searched for cases of IDSNC with available cytologic materials. All available slides were reviewed and a detailed morphological analysis was performed. RESULTS: Six cases were identified from 6 patients. FNA specimens were obtained from metastatic sites (4 cases), a local disease recurrence (1 case), and a primary lesion extending into the orbit (1 case). The majority of cases had cellular specimens with features of nonkeratinizing squamous cell carcinoma composed of cohesive clusters and sheets of oval to polygonal cells with indistinct cell borders present within a background of necrotic debris. Two cases had single rhabdoid cells with more abundant cytoplasm. The nuclei generally were small and uniform with fine chromatin, small nucleoli, and mild nuclear membrane irregularities; moderate anisonucleosis and multinucleation were noted in one case. Apoptotic bodies were common in 5 of 6 cases, and readily identifiable mitoses in 3 of 6 cases. Immunohistochemistry demonstrated that all cases expressed cytokeratins, 4 of 5 cases expressed p63, and all cases demonstrated loss of INI-1 nuclear expression. All cases were negative for neuroendocrine markers and aberrant p16 staining. CONCLUSIONS: A diagnosis of IDSNC can be suspected on FNA specimens from patients with high-grade sinonasal carcinomas that have either a nonkeratinizing squamous cell carcinoma or rhabdoid morphology. Clinical history and the availability of material for immunohistochemistry are key in confirming the diagnosis. Cancer Cytopathol 2018.