Colon cancer is the second most common cancer in adults and second major cause of cancer deaths in United States. Its incidence has much decreased in the last two decades due to early detection via screening and availability of good treatment options for early stage tumor. Age more than 50 years, presence of polyp (an outgrowth in the colon lumen from its wall due to excessive proliferation of cells), loss of function of certain genes, more intake of fats and red meat and tobacco smoking are all possible risk factors for the development of colon cancer¹.

Colon Cancer Staging

Colon cancer like almost all other cancers has ability to spread, and colon cancer staging measures this ability. Simply, the staging is a process by which we determine the extent of spread of cancer from its original primary location^1-3. Colon cancer staging tells us that whether the cancer is present within the colon wall or it has spread to the other organs of the body. Staging of colon cancer is important because it helps us to select a proper treatment option for the colon cancer.

Spread of colon cancer³: Almost every cancer has property to spread from its primary site; this property is termed as metastasis. The metastasis is one of the important parameter in colon cancer staging. Colon cancer can spread by three ways:

• Direct spread to entire colon wall, urinary bladder and ureter, ovaries and uterus.
• Lymphatic spread (spread through lymph vessels) to different group of lymph nodes.
• Blood spread to liver, bone, lung and skin.

Investigations for colon cancer staging: Following investigations are carried out for staging of colon cancer^1-3:

• CT Chest to determine the spread of cancer to lungs
• CT Abdomen and pelvis to determine the spread of cancer to liver, lymph nodes, ovary, uterus, ureter, urinary bladder and rectum.
• Ultrasonography of abdomen to determine liver involvement
• Pelvic MRI and endorectal Ultrasonography identifies the depth of penetration of cancer through colorectal wall and adjacent lymph nodes
• Dissection of involved lymph nodes
• Liver function tests to see liver involvement
• Complete blood count to see bone involvement
• Bone scan to see bone involvement
• Colonoscopy and biopsy of the involved area.

Types of Staging of Colon Cancer: Following are some types of staging of colon cancer³:

• Duke’s staging
• Modified Duke ‘staging
• Astler-Coller’ staging
• TNM-system

Duke’s staging3: According to this staging extent of colon cancer can be described in three stages:

• Cancer confined to bowel wall but not involving whole thickness of wall and lymph nodes.
• Cancer involving entire thickness of bowel wall but not involving the lymph nodes.
• Lymph nodes are also involved along with entire colon wall.

Modified Duke’s staging3: according to this staging extent of colon cancer can be described into four stages:

1. Cancer limited to colorectal bowel wall.
2. Cancer extending up to tissues around the colorectal wall but not involving lymph node.
3. Lymph node involvement.
4. Cancer with distant spread to liver, lungs, bone and brain.

Astler-Coller’s staging3: It includes following stages of colon cancer:
A. Cancer involving inner third of bowel wall
B1. Cancer involving inner two third of bowel wall
B2. Cancer involving entire thickness of bowel wall and spread into peritoneum

C1. Cancer involving inner two third of bowel wall and involvement of lymph nodes
C2. Cancer involving entire thickness of bowel wall and spread into peritoneum and involvement of lymph nodes

D.Distant spread of cancer.

TNM- staging3: The TNM-staging is more commonly used classification than above described types to stage colorectal cancer. It uses three parameters to stage the colon cancer i.e.

• T- Which means invasion of colon cancer
• N- Which means involvement of lymph node
• M- Which means metastasis or spread to distant organs

According to this system colon cancer can be staged as follows:

Tsitu-Carcinoma in situ that means cancer without invasion

T1- Invasion into submucosa (inner third of bowel wall)

T2- Invasion into muscularis (inner two third of bowel wall)

T3- Invasion into fat surrounding the bowel wall

T4- Invasion into the adjacent organs

N0- No lymph node involvement

N1- Up to three lymph nodes are involved

N2- Four or more than four lymph nodes are involved

M0- No distant spread is present

M1- Distant spread is present

An illustration of staging of colon cancer is given below⁴:

Colon Cancer Staging and Prognosis

The stage of colon cancer at presentation is the most important determinant of long term survival. The patients with colon cancer involving only colonic submucosa without lymph node involvement or distant spread have survival rate of more than 90%. The patients with colon cancer involving less than 4 lymph nodes have survival rate of 67%. The patients with colon cancer involving more than 4 lymph nodes have survival rate of 33%. The patients with colon cancer involving distant organs have survival rate of 5-7%¹. Prognosis also depends upon the following facts³:

• Site- Left sided cancer has better prognosis as they present early
• Type- Colloid cancer (histological type of colon cancer) has got poorer prognosis
• Size- Large sized tumor has got poorer prognosis
• Associated diseases like AIDS make the prognosis poor.
• Age- Age more than 50 years makes the prognosis poor.

Another illustration of staging for colon cancer is given below⁵:

References

1. Papadakis MA, Macphee SJ, editors. Current Medical Diagnosis and Treatment.52^nd ed. New York: Mc Graw Hill Medical; 2013.
2. Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, ed. New Delhi: Mc Graw Hill Medical; 2012.
3. Bhat S. SRB’s manual of surgery. 3^rd ed. New Delhi: Jaypee Brothers Medical Publishers (P) Ltd; 2009.
4. Colonoscopy and colyte can be fun if you do it right [Internet]. 2011 [cited 2013 July 17]. Available from: https://www.probaway.com/helps/.
5. Staging colon cancer [Internet]. 2012 [cited 2013 July 21]. Available from: https://www.thecolorectalinstitute.com/staging-colon-cancer/.