Comprehensive analysis of HPV infection,EGFR exon 20 mutations and LINE1 hypomethylation as risk factors for malignant transformation of sinonasal-inverted papilloma to squamous cell carcinoma

Different risk factors are suspected to be involved in malignant transformation of sinonasal papillomas and include HPV infection, tobacco smoking, occupational exposure, EGFR/KRAS mutations and DNA methylation alterations. In our study, 25 inverted sinonasal papillomas (ISPs), 5 oncocytic sinonasal papillomas (OSP) and 35 squamous cell carcinomas (SCCs) from 54 patients were genotyped for 10 genes involved in EGFR signalling. HPV-DNA detection was performed by in-situ hybridisation and LINE-1 methylation was quantitatively determined by bisulphite-pyrosequencing. High-risk HPV was observed only in 13% of ISP-associated SCC and in 8% of de novo-SCC patients. EGFR mutations occurred in 72% of ISPs, 30% of ISP-associated SCCs and 17% of de novo-SCCs. At 5-year follow-up, SCC arose in only 30% (6/20) of patients with EGFR-mutated ISPs compared to 76% (13/17) of patients with EGFR-wild-type ISP (p = 0.0044). LINE-1 hypomethylation significantly increased from papilloma/early stage SCC to advanced stage SCC (p = 0.03) and was associated with occupational exposure (p = 0.01) and worse prognosis (p = 0.09). In conclusion, our results suggest that a small subset of these tumours could be related to HPV infection; EGFR mutations characterise those ISPs with a lower risk of developing into SCC; LINE-1 hypomethylation is associated with occupational exposure and could identify more aggressive nasal SCC.