Squamous cell carcinoma in situ involving mesonephric remnants of the uterine cervix.

Squamous cell carcinoma in situ (CIS) involving mesonephric remnants of the uterine cervix is a very rare lesion, the existence of which is still controversial. A second case of this lesion is reported. It was found in a cone biopsy specimen from an 40-year-old patient. Besides, in surface epithelium and within cervical glands, a structure of CIS was seen in conjunction with mesonephric tubules in deeper cervical stroma. The mesonephric nature of these tubules and of tubule-appearing epithelium within islands of CIS was supported by immunohistochemical positivity for CD10 and vimentin. The lesion strongly simulated invasive carcinomas, such as adenosquamous carcinoma and adenoid basal carcinoma (epithelioma) of the cervix.