Definition of Carcinoma in situ

Pancreatic Cancer Slideshow

Carcinoma in situ: Cancer that involves only the place in which it began and that has not spread. Carcinoma in situ is an early-stage tumor.

For example, squamous cell carcinoma in situ (Bowen's disease) is an early cancer of the skin. It develops from squamous cells which are flat, scalelike cells in the outer layer of the skin (the epithelium).

The term "in situ" (borrowed from the Romans) means "in the natural or normal place" and, in the case of cancer, it means that the tumor cells are still confined to the site where they originated and they have neither invaded neighboring tissues nor metastasized afar. The tumor is curable.