How is cancer in situ?

AKA intraepithelial carcinoma/non-invasive, proliferation of malignant epithelia not crossing basement membrane, application in tumors of covering, separated from vascularized CT by basement membrane, seen in squamous cells of vagina, skin, esophagus, squamous epithelium of bronchi, paramalpigean of bladder, glandular (mammary), digestive mucus membranes. Usually not sarcoma (only theory), but malignant melanoma there are many in situ (intraepidermal melanoma/ SSM) Screening is important for tx, can remain in situ for years, but if untreated it will become invasive.