Long-term follow-up of a Patient with Malignant Transformation of Inverted Papilloma into Sinonasal Undifferentiated Carcinoma

Introduction Inverted papillomas (IP) are benign sinonasal neoplasms, which account for 0.5–4% of all nasal tumors. IPs have been known to transform into squamous cell carcinoma in 5–15% of cases. Rarely, transformations to other malignancies have been reported. Here we report a unique case of malignant transformation of an IP into sinonasal undifferentiated carcinoma (SNUC). Methods A case report with a literature review; institutional review board exempted. The clinical presentation, radiographic features, surgical intervention, histopathologic analysis, treatment, and outcome of the case were examined. Results A 62-year-old man presented with a 3-month history of nasal airway obstruction, rhinorrhea, and postnasal drip refractory to medical therapy. He had a long history of exposure to fumes, chemicals, dusts, and solvents as a professional painter as well as a 45 pack-year history of smoking and alcohol abuse. The patient was ultimately found to have a left ethmoidal IP with a focus of malignant transformation into SNUC. Endoscopic resection was performed, followed by concurrent chemoradiation and adjuvant chemotherapy. After surgery, he had no evidence of recurrent disease after 9 years of follow-up. Conclusions IP is known to transform into squamous cell carcinoma. Here we report a rare case of malignant transformation into SNUC, a much more uncommon and aggressive lesion. Although traditionally associated with a poorer prognosis, the positive outcome for SNUC observed in this patient may potentially be attributed to early detection and timely therapeutic intervention