Carcinoma in situ (CIS) is a group of abnormal cells. While they are a form of neoplasm, there is disagreement over whether CIS should be classified as cancer. This controversy also depends on the exact CIS in question (e.g., cervical, skin, breast). Some authors do not classify them as cancer, however, recognizing that they can potentially become cancer. Others classify certain types as a non-invasive form of cancer. U.S. surgical pathologist Albert C. Broders introduced both the term and concept of carcinoma in situ in 1932. The term "pre-cancer" has also been used.
These abnormal cells grow in their normal place, thus in situ (Latin for 'in its place'). For example, carcinoma in situ of the skin, also called Bowen's disease, is the accumulation of dysplastic epidermal cells within the epidermis only, that has failed to penetrate into the deeper dermis. For this reason, CIS will usually not form a tumor. Rather, the lesion is flat (in the skin, cervix, etc.) or follows the existing architecture of the organ (in the breast, lung, etc.). Exceptions include CIS of the colon (polyps), the bladder (preinvasive papillary cancer), or the breast (ductal carcinoma in situ or lobular carcinoma in situ).
