Squamous cell carcinoma in situ involving mesonephric remnants. A potential diagnostic pitfall

A case of uterine cervical squamous cell carcinoma in situ (CIS) in which there was extensive endocervical glandular involvement was found to have, in addition, a deep-seated squamous epithelial lesion within the cervical stroma. Because of the deep location of this lesion, which was composed of nests of pleomorphic squamous epithelial cells, found at a site not usually occupied by endocervical glands, it was initially thought to be an invasive squamous cell carcinoma (SCC). However, on review it was found that there was CIS in the deep cervical stroma that appeared to involve small tubular structures and dilated ducts that were lined by mucin-free cuboidal epithelial cells. There was no stromal reaction to this lesion. Tubules had a poorly defined lobular arrangement and had intraluminal bright eosinophilic hyaline material. Tubular epithelial cells demonstrated immunohistochemical staining for low-molecular-weight keratin (LMWK) and vimentin but showed no staining for carcinoembryonic antigen (CEA) and high-molecular-weight keratin (HMWK). It was apparent that these tubular structures and ducts were mesonephric remnants and that this lesion represented involvement of mesonephric remnants by CIS. Although involvement of endocervical glands by CIS is well recognized, a similar lesion involving mesonephric remnants has not been previously described. Familiarity with the histological features of these lesions is essential to avoid a misdiagnosis and potential mismanagement.