Sinonasal inverted papillomas (SNIPs) are derived from the benign tumors of the epithelial cells and have the potential to recur and exhibit malignant characteristics. The aim of the present study was to investigate the clinicopathological features and prognosis of patients with malignant transformation of SNIP. A total of 32 consecutive cases, who were patients at the Department of Otorhinolaryngology Head and Neck Surgery, Tianjin Huanhu Hospital from January 1991 to January 2008, were retrospectively reviewed. Survival rates and prognostic factors were calculated using the Kaplan‑Meier method and multivariate Cox model survival analysis. The malignancy accounted for 8.99% of all types of SNIP. There were 25 males and seven females, and the median age of onset was 56.5 years. The sites of tumor included 22 in the nasal cavity and ethmoid sinuses, and 10 in the maxillary sinus. The tumors included 21 high‑grade tumors, eight intermediate‑grade tumors and three low‑grade tumors. The number of patients with T1, T2, T3 and T4 stage disease was three, 10, 16 and three, respectively, according to the American Joint Committee on Cancer staging method. Based on the percentage of malignant cells in the entire tumor tissue, five patients had grade Ⅰ tumors, five had grade Ⅱ, eight had grade Ⅲ and14 had grade Ⅳ. Among the 32 patients, three cases exhibited distant metastasis, and 19 patients underwent surgery plus postoperative radiotherapy, 10 underwent surgery alone and three underwent radiotherapy alone. The 5‑year survival rate was 72.5% and the median overall survival time was 62.2 months. Kaplan‑Meier univariate survival analysis indicated that the clinical stage and treatment method were prognostic factors, and multivariate Cox model survival analysis confirmed that the clinical stage and treatment method were independent factors for overall survival (relative risk: 4.211 and 0.312, respectively; P<0.05 for both). T3 and T4 staging and mono-treatment were associated with poor patient survival. Overall, the present study identified that the morbidity of SNIP‑associated malignancy was low, the clinicopathological features were not specific, and the prognosis was improved compared with other types of sinonasal squamous cell carcinoma. The clinical stage and treatment method were found to affect the prognosis, and surgery plus postoperative radiotherapy was the predominant form of treatment. The present study may improve the understanding of the prognosis for patients with malignant SNIP in the future.

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