Conjunctival inverted squamous papilloma: a case report with immunohistochemical analysis and review of the literature.

A 63-year-old man presented with an asymptomatic papillary, sessile lesion of the juxtalimbal bulbar conjunctiva that was surgically excised with cryotherapy. Histopathologically, the lesion created some diagnostic confusion as it displayed an endophytic, or inverted, growth pattern-with squamous cells pushing into the substantia propria around fibrovascular cores, but without significant cytologic atypia, consistent with a conjunctival inverted papilloma (IP). Unlike previously reported cases of conjunctival IP, there were no goblet cells or cysts within the tumor. Immunostaining was diffusely positive for cytokeratin (CK) 7, and CK14 stained the basilar and suprabasilar cells, as in normal conjunctiva. CK17 weakly and non-uniformly stained the tumor, ruling out a dysplasia, which is usually strongly positive. The lesion's cytokeratin profile therefore paralleled that of normal conjunctiva. The proliferation index with Ki67 nuclear staining was extremely low (<1%), as was p53 nuclear staining (10-20%), both in contrast to squamous cell dysplasias or carcinomas that have a much higher percentage of positive cells. The lesion was negative for human papillomavirus subtypes associated with squamous neoplasias including carcinomas. We review the previous literature devoted to this comparatively rare condition and contrast its benign clinical course with that of inverted papillomas of the sinonasal, lacrimal drainage, and genitourinary systems and provide a set of criteria for establishing the diagnosis.