Pathogenesis of Sinonasal Inverted Papilloma: Multistep Development and Its Malignant Change

Sinonasal inverted papilloma (IP) has been shown its dynamic range of clinical spectrum. It shows as an inflammatory polyp in some cases, and on the other hand it shows just space occupying benign tumor in the sinonasal cavity. Sometimes it shows even infiltrating and destructive character toward surrounding tissue. Pathologically it also has been shown broad scope from squamous metaplasia to squamous inversion to dysplasia to squamous carcinoma change. Two natures of IP, inflammatory and neoplastic characters, have been considered to involve in the pathogenesis of IP. Mostly neoplastic characters such as abnormality of cell cycle or cell stability, and genetic changes have been reported so far. However, the tissue samples mostly used have serious problem of heterogeneity, which include all lesions of squamous metaplasia, squamous inversion, dysplasia and even squamous carcinoma changes. Moreover, the role of inflammation is not well understood. Authors have studied several research using tissue samples which exactly classified according to pathologic grade. With these results, we could hypothesize a model of multistep development and its malignant change of IP.