[SMARCB1 (INI1)-deficient sinonasal carcinoma: a clinicopathological analysis of six cases]

Objective: To study the clinicopathological features, diagnostic features and differential diagnoses of SMARCB1 (INI1)-deficient sinonasal carcinoma (SDSC). Methods: Six cases of SDSC diagnosed at Eye, Ear, Nose and Throat Hospital, Fudan University from 2016 to 2018 were retrieved; the clinical features, histomorphology, immunophenotype, radiology and outcome were analyzed with review of literature. Results: There were five men and one woman with age range of 37 years to 75 years (mean 56 years). One case was in stage T2, and 5 cases were in stage T4. Computer tomography and magnetic resonance imaging showed a mass occupying the sinonasal cavity with bone destruction in all six patients. Microscopically, the tumors had infiltrative margins. Four tumors were composed mostly of basaloid cells, which possessed high nuclear/cytoplasmic ratio,scant cytoplasm,and minimalnuclear pleomorphism; and the cells were arranged in sheets or nests in a desmoplastic stroma. Two tumors were composed of rhabdoid cells, which possessed abundant, eosinophilic cytoplasm and eccentric nuclei, often growing in a nests or sheets pattern. Immunohistochemical staining showed that 6/6 cases had complete loss of INI1, diffusely and strongly positive for CKpan, and were negative for S-100 and EBER ISH; 4/6 cases were focally positive for p63; 1/5 was focally positive for Syn and p16. The Ki-67 index was 30% to 70%. The follow-up period ranged 1-26 months, with one patient died of extensive metastases, one had local recurrence, and two had lymph node metastases; one was alive without disease, and one was lost to follow-up. Conclusions: SMARCB1 (INI1)-deficient sinonasal carcinoma is mostly aggressive, with rapid progression and poor prognosis. Histomorphological spectrum predominantly consists of basaloid type and rhabdoid type. The complete loss of nuclear expression of INI1 can help to distinguish this tumor from its many mimickers.