Primary squamous cell carcinomas of the endometrium. Clinico-pathologic data and histogenetic classification

Primary squamous cell carcinomas of the endometrium are rare tumours. We have studied 7 primary and 2 secondary squamous cell carcinomas immunohistochemically with anti-all-cytokeratin (KL 1), anti-CEA and anti-vimentin. The non-keratinizing carcinomas and the non-keratinizing component of the keratinizing carcinomas showed a strong expression of vimentin. Contrary to this, the keratinizing parts were strongly positive with anti-CEA. Additionally, some cases showed a direct transformation of the (dysplastic) glandular endometrial epithelium into neoplastic squamous cells. These findings suggest that the primary squamous cell carcinoma of the endometrium is the result of a bidirectional differentiation of pluripotent endometrial precursor cells. Like in other non-endometrioid adenocarcinomas, such metaplasias develop from pluripotent Müllerian epithelium. They show various differentiations, perhaps endocervical determination with keratinization and positive reaction against CEA or primitive endometrioid with squamous cell appearance, positive anti-vimentin reaction and non-keratinization.