If there is a tendency toward squamous differentiation (keratin pearls, individual keratinization, intercellular bridges, or strong p40 immunoreactivity) and/or glandular differentiation (acinar architecture, nuclear polarization, rudimentary glands with mucin production, or strong immunoreactivity for carcinoembryonic antigen or mucin), a diagnosis should be made according to the corresponding histological type (squamous cell carcinoma, adenocarcinoma, or adenosquamous carcinoma). This evidence concerns the gene CEACAM5 and adenosquamous carcinoma.