A malignant epithelial neoplasm confined to the squamous epithelium, without invasion of the underlying tissues. The disease is squamous carcinoma in situ (MONDO_0004693, a Monarch Disease Ontology entry). Also known as: carcinoma, squamous cell, in situ, malignant, epidermoid carcinoma in situ, epidermoid cell carcinoma in situ, grade 3 SIN, grade 3 squamous intraepithelial neoplasia, grade III SIN, grade III squamous intraepithelial neoplasia, intraepithelial squamous cell carcinoma.