When it comes to cancer staging, people often hear about stages 1, 2, 3, and 4 of cancer. However, there is actually stage zero cancer that, as you might guess, comes before stage 1. Stage zero cancer is also known as carcinoma in situ. Carcinoma in situ cells are limited to the location where they first formed, such as within the epithelial layer of the mucosa or the epidermis of the skin, and have not spread to surrounding tissue.
Theoretically, most cancers develop from carcinoma in situ, but not all cancers can be detected at the earliest stages. Carcinoma in situ is relatively common in the diagnosis of the following cancers.
