Colon Cancer Staging: TNM Classification Of Colorectal Cancer

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Colon cancer TNM staging helps to determine the disease prognosis and to select an appropriate treatment strategy.

TNM is the most commonly used staging system for colorectal cancer. It uses mainly 3 parameters: “T” stands for “Tumor”; “N” for “Lymph Nodes”; and “M” for “Metastasis”. Numbers and/or letters after T (0, is, 1, 2, 3, and 4), N (0, 1, and 2), and M (0 and 1) provide more details about each of these parameters. Once T, N, and M are determined, it is used to assign an overall stage (from 0 to IV).

T STAGING

Tis – Pre-cancerous or cancer cells present only in the superficial layer (epithelium) of colorectal mucosa

T1 – Cancer extends to the lamina propria

T2 – Cancer extends to the muscular layer (muscularis propria)

T3 – Cancer extends through the muscularis propria into the pericolorectal tissues 

T4a – Cancer has invaded up to the outermost serosa layer (or visceral peritoneum) 

T4b – Cancer has invaded into the adjacent structures/organs like small intestine, kidneys, pancreas, or stomach 

Colon cancer TNM Staging

N STAGING

N0 – Cancer has not spread to regional lymph nodes

N1 – Cancer has spread to 1 to 3 nearby lymph nodes

N2a – Cancer has spread to 4 to 6 nearby lymph nodes.

N2b – Cancer has spread to >/=7 nearby lymph nodes.

M STAGING

M1a – Cancer has spread to one distant organ without peritoneal spread.

M1b – Cancer that has spread to >/=2 distant organs without peritoneal spread.

M1c – Cancer that has spread to peritoneum with or without other sites.

colon cancer N and M staging

Following table describes the detailed TNM staging for colorectal cancer:

StageTNM
0 Tis N0 M0
I T1-2 N0 M0
IIA T3 N0 M0
IIB T4a N0 M0
IIC T4b N0 M0
IIIAT1-2 N1/1c M0
T1 N2a M0
IIIBT3-4a N1/1c M0
T2-3 N2a M0
T1-2 N2b M0
IIICT4a N2a M0
T3-4a N2b M0
T4b N1-2 M0
IVAAny T Any N M1a
IVBAny T Any N M1b
IVCAny T Any N M1c

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Watch the video below to know the NORMAL ANATOMY that will help to understand the staging better.

Video Transcript:

This pouch-like structure, present at the beginning of the colon is called as caecum.

This part, present on the right side of the abdomen, extending upwards from the caecum is called an ascending colon.

The longest part of the colon, that extends from the right to the left side of the abdomen, is called as transverse colon.

And this part, which extends downwards from transverse colon, on the left side of the abdomen, is called as descending colon.

And this last part, which connects colon to the rectum and anal canal is called as sigmoid colon.

These are the loops of the small intestine that occupy the central part of the abdomen.

This is the cross-section from the wall of the colon, with the upper part being inside and lower part being outside of the wall.

The innermost layer is epithelium, followed by this layer called as lamina propria.

Outer to which lies muscularis mucosa. Then comes the submucosa. Outer to which lies the muscularis propria which is followed by a layer of pericolorectal tissue.

On the outermost aspect, lies this layer which is called as serosa.

TNM Staging for colon cancer video:

Video Transcript:

Now we will discuss the T-staging for colon cancer.

Tis is the disease which is limited to the epithelium. If it infiltrates into the lamina propria or muscularis mucosa, it is called as T1a. And T1b, when it infiltrates into the submucosa. Infiltration into muscularis propria is called as T2 disease. Pericolorectal tissue infiltration is called as T3 disease. And infiltration of serosa is called as T4a. If the tumor infiltrates through the wall of colon, to involve the surrounding structures, it is called as T4b.

A tumor present in almost any part of the colon may infiltrate into the small intestine.

Tumor in the ascending colon may infiltrate into the right kidney. And that in the descending colon may infiltrate into the left kidney.

A transverse colon tumor may extend to involve pancreas. And may even extend to involve the stomach.

Now we will discuss the N staging or the nodal staging for colon cancer. In this figure, you can see the draining lymph nodes for the colon.

 

It can be called as N1 or N2, depending upon the number of lymph nodes involved.

Lastly, we will discuss the M-staging or the metastatic staging of the colon cancer.

As you can see in the figure, the venous drainage from most of the part of colon, ultimately pass through the liver.

So liver is the most common site for the distant spread of the tumor from colon.

As you can see in this figure, the tumor in the right side of colon has spread to the liver.

In this figure, a left sided tumor has spread to the liver.

Due to the direction of vascular drainage, after liver, lungs are the second most common organs involved by metastasis.

This figure shows the spread of colon cancer to both the lungs, in form of multiple nodular deposits.

And sometimes, both lungs and liver maybe involved in the metastatic spread of the disease, as we can see in this figure.

The tumor may also spread to the peritoneum, in form of peritoneal deposits.

It may rarely spread to one or both the ovaries. Very rarely, the tumor may also spread to the brain or bones.

So with this, we finish the TNM staging for colon cancer.

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