Colorectal Cancer In Situ

Big words and cancer diagnoses are very frightening -- but sometimes big words in your diagnosis don't mean bad things. If there is a preferable type of cancer to get diagnosed with, it would be carcinoma in situ. The word "carcinoma" means cancer and "in situ" roughly translates to in the original place. Following a cancer diagnosis, hearing that your cancer is in situ is the best possible news you can get.

You will not know what degree of colorectal cancer you have until after surgical removal and the cancer is staged. There is a specific staging system created by the American Joint Committee on Cancer. This system uses a combination of letters and numbers to briefly and accurately depict how early or advanced your cancer is. The three letters used are T, N, and M.

The letter T stands for tumor. The numerals following this letter explain, on a 0-4 scale, how invasive your primary tumor is in its original location. The higher the number, the more invasive the tumor. For instance, a very invasive cancer that has spread through all four layers of the colon wall would be staged as a T4. There are also further subsets with lower case letters, to add an even more detailed description.

There is one exception when you will not see a number following the T. If you are diagnosed with carcinoma in situ, or the earliest possible stage of cancer, your T will precede the letters "is" and look like this: Tis.


You want to see these three letters if you've been told you have cancer. The Tis means that the cancer was caught so early that it has not made it past the first, innermost layer of your colon. In most cases, this is the most easily treatable form of colorectal cancer. The majority of these types of colon cancer are treated with surgical removal of the affected tissues via a colonoscopy.

The N part of staging stands for node. Your treatment plan will likely depend in part on the number following the N -- this time between 0 and 2 -- with 0 being the most desirable and 2 meaning the cancer has spread to four or more lymph nodes outside of the colon. If you have carcinoma in situ, your N will look like this: N0. This means that the cancer has not even left the innermost lining of your colon, and it also did not make it to any nearby lymph nodes. 

M stands for metastasis. If there is anything behind the M other than a zero, it means that the colon cancer has spread outside of the colon to other organs within your body. The letters M1a and M1b are used to depict how many organs are affected. 

To bring it all together, if you have carcinoma in situ, your staging would appear as: Tis N0 M0. This is also known as Stage 0 colorectal cancer. The fact that this stage of colon cancer is so easily treatable is the reason why colonoscopies are encouraged routinely. The majority of polyps take years to turn cancerous -- and some polyps will never become cancer.

However, if you have routine colonoscopies, your doctor can remove the polyps that might develop into cancer or catch cancer very early, when it remains in situ.

These three letters and their trailing numerals play a large role in your treatment plan. Your doctor will  consider your overall health and the stage of  your cancer prior to suggesting a cancer treatment plan for you. Carcinoma in situ is almost always treated surgically, and Stage 0 cancer does not typically require any adjuvant treatment such as chemotherapy or radiation. 


American Cancer Society. (n.d.). How is Colorectal Cancer Staged? Accessed online March 14, 2015.

Canadian Cancer Registry. (2011). High Grade Dysplasia and Carcinoma In Situ -- Are They Synonymous? NAACCR Conference, Kentucky. Presentation accessed online March 20, 2015.

Continue Reading