Carcinoma in situ (CIS), also known as in situ neoplasm, is a group of abnormal cells.〔〔(【引用サイトリンク】url=http://apps.who.int/classifications/icd10/browse/2010/en )〕 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 (i.e. cervical, skin, breast). Some authors do not classify them as cancer recognizing that they can potentially become cancer. Others classify certain types as a non-invasive form of cancer. The term "pre-cancer" has also been used.
These abnormal cells grow in their normal place thus "''in situ''" (from 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 (pre-invasive papillary cancer), or the breast (ductal carcinoma ''in situ'' or lobular carcinoma ''in situ'').
Many forms of CIS have a high probability of progression into cancer,〔Ridge JA, Glisson BS, Lango MN, et al. ("Head and Neck Tumors" ) in Pazdur R, Wagman LD, Camphausen KA, Hoskins WJ (Eds) (Cancer Management: A Multidisciplinary Approach ). 11 ed. 2008.〕 and therefore removal may be recommended; however, it is well-known that progression of CIS is highly variable and not all CIS becomes invasive cancer.
In the TNM classification, carcinoma ''in situ'' is reported as TisN0M0 (Stage 0).〔(【引用サイトリンク】title=Cancer Staging Fact Sheet )〕
These terms are related since they represent the steps of the progression toward cancer:
*Dysplasia is the earliest form of pre-cancerous lesion recognizable in a biopsy. Dysplasia can be low grade or high grade. High grade dysplasia may also be referred to as carcinoma ''in situ''.
*Invasive carcinoma, usually simply called cancer, has the potential to invade and spread to surrounding tissues and structures, and may eventually be lethal.
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