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.
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 situ or
lobular 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]
Terminology
These terms are related since they represent the steps of the progression toward cancer:
Dysplasia is the earliest form of precancerous 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.
Examples
Cervical
squamous intraepithelial lesion (SIL), previously called cervical intraepithelial neoplasia (CIN), is a form of
dysplasia that can progress to
cervical cancer. The term carcinoma in situ may be used interchangeably with high-grade SIL.[8]
Bronchioloalveolar carcinoma (BAC) of the lung is the only form of CIS that can kill directly because, in rare cases (the "pneumonic form"), it expands greatly and fills the lungs, preventing breathing and causing other dire effects on the host. Thus, the pneumonic form of BAC is a true
malignant entity, but is not "invasive" in the classical sense. For this reason, it is considered a form of CIS by
pathologists, but not by
oncologists or
surgeons, and inclusion of this form of cancer among the types of CIS is controversial.
Treatment
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.