Carcinoma in situ (CIS) is a group of abnormal cells.[1][2] While they are a form of neoplasm,[3] 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, however, recognizing that they can potentially become cancer.[1] Others classify certain types as a non-invasive form of cancer.[4][5] The term "pre-cancer" has also been used.
| Carcinoma in situ | |
|---|---|
| Other names | in situ neoplasm |
 | |
| Specialty | Oncology |
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 (preinvasive papillary cancer), or the breast (ductal carcinoma in situorlobular carcinoma in situ).
Many forms of CIS have a high probability of progression into cancer,[6] and therefore removal may be recommended; however, progression of CIS is known to be highly variable and not all CIS becomes invasive cancer.
In the TNM classification, carcinoma in situ is reported as TisN0M0 (stage 0).[7]
These terms are related since they represent the steps of the progression toward cancer:
Carcinoma in situ is, by definition, a localized phenomenon, with no potential for metastasis unless it progresses into cancer. Therefore, its removal eliminates the risk of subsequent progression into a life-threatening condition.
Some forms of CIS (e.g., colon polyps and polypoid tumours of the bladder) can be removed using an endoscope, without conventional surgical resection. Dysplasia of the uterine cervix is removed by excision (cutting it out) or by burning with a laser. Bowen's disease of the skin is removed by excision. Other forms require major surgery, the best known being intraductal carcinoma of the breast (also treated with radiotherapy).