Penile Analogue of Stratified Mucin-Producing Intraepithelial Lesion of the Cervix: The First Described Case. A Diagnostic Pitfall

The authors report a case where undifferentiated (classic) penile intraepithelial neoplasia was associated with the presence of goblet cells throughout the full epithelial thickness and which later progressed into an invasive carcinoma. The lesion evolved in three consecutive biopsies from only surface epithelium occupying numerous goblet cells in the first to variably sized solid nodules in the dermis composed of atypical squamous and/or basaloid cells intermixed with numerous goblet cells in the third biopsy. Both cellular components expressed CK7 and p16 protein. Human Papillomavirus (HPV) genotyping revealed high risk HPV type 16. To the best of our knowledge, this is the first description of such a lesion occurring on the penis, which can be considered the penile analogue of cervical stratified mucin-producing intraepithelial lesion (SMILE). The correct diagnosis was rendered retrospectively, after recognition of the existence of a vulvar lesion resembling cervical SMILE. The initial biopsy was misinterpreted as extramammary Paget disease, which also constitutes the main pitfall in the differential diagnosis. Another important differential diagnosis is penile/vulvar mucinous metaplasia. The finding of atypical squamous epithelial cells positive for p16 associated with mucinous cells present throughout the full epithelial thickness is a clue to the diagnosis of penile SMILE.