The most severe cases of dysplasia are sometimes referred to as "carcinoma in situ." 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. However, carcinoma in situ may develop into an invasive, metastatic malignancy and, therefore, is usually removed surgically, if possible. 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). source 1:Carcinoma in situ definition - Cancer Information (Cancers, Symptoms, Treatment) on MedicineNet.com source 2:Comprehensive Cancer Information - National Cancer Institute
