In medicine, carcinoma is any cancer that arises from epithelial cells. It is malignant by definition: carcinomas invade surrounding tissues and organs, and may spread to lymph nodes and distal sites (metastasis). Carcinoma in situ (CIS) is a pre-malignant condition, in which cytological signs of malignancy are present, but there is no histological evidence of invasion through the epithelial basement membrane.
Types of carcinoma
Carcinoma, like all neoplasia, is classified by its histopathological appearance. Adenocarcinoma and squamous cell carcinoma, two common descriptive terms for tumours, reflect the fact that these cells may have glandular or squamous cell appearances respectively. Severely anaplastic tumours might be so undifferentiated that they do not have a distinct histological appearance.
Carcinomas, like all cancers, are staged according to the extent of disease. The UICC/AJCC TNM system is often used, however for some common tumours, classic staging methods (such as the Dukes classification for colon cancer) are still used.