Carcinoma in situ

This page was reviewed under our medical and editorial policy by

Maurie Markman, MD, President, Medicine & Science

This page was updated on April 21, 2022.

Carcinoma in situ refers to a group of abnormal cells that have not spread from the location where they first formed, although they may later spread into normal tissue and become cancer.

Carcinoma in situ, also called in situ cancer or cancer in situ, is different from invasive carcinoma, which has spread to surrounding tissue. It also differs from metastatic carcinoma, which has spread throughout the body to other tissues and organs. In general, carcinoma in situ is the earliest form of cancer, and is considered stage 0.

In situ cancer examples

An example of carcinoma in situ is ductal carcinoma in situ, or DCIS, which is considered an early form of breast cancer and occurs when abnormal cells form a breast’s milk duct. According to the American Cancer Society, an estimated one in five new breast cancers each year will be diagnosed as DCIS.

Stage 0 basal cell carcinoma is another example of carcinoma in situ. This early-stage skin cancer is only found in the epidermis and has not spread more deeply into the dermis.

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