The large intestine in humans is divided into the colon, rectum, and anus. The colon is the largest part of the large intestine. Various types of cells are present in the colon. Mutations in one or more cell types may result in uncontrolled growth and division. This condition involving uncontrolled growth and division of colon cells leading to tumor formation is known as colon cancer or colon carcinoma.
Although colon carcinoma may develop in people of any age, it most often occurs in the elderly. The initial stage of colon cancer is the formation of polyps. Although not all polyps turn into cancer, the presence of polyps significantly increases the risk of colon cancer. Men are at a higher risk of developing this condition than women.
Colon carcinoma is slowly becoming one of the most prevalent cancers in India. The survival rates for this disease are relatively lower in India as compared to developed countries, and probable reasons for this include delayed diagnosis and limited access to better quality healthcare.
Also, another important aspect is that colon cancer incidence in India is likely under-reported due to underdiagnosis and limited access to healthcare in rural areas.
Based on the type of cell that it arises from, colon cancer is classified into various types. Different types of colon cancer include:
Several glandular cells are present in the colon and produce mucus. The mucus is important for lubrication and protection of the internal wall of the colon. The cancer of these gland cells in the colon is known as colon adenocarcinoma. It is the most common type of colon carcinoma.
Squamous cell carcinoma arises from squamous cells, and it is exceptionally uncommon, as compared to other types of colon cancer.
Carcinoid tumors are types of neuroendocrine tumors that are slow-growing. Carcinoid tumors usually do not cause any symptoms and are diagnosed incidentally. Due to their slow growth rate, they have very little potential to metastasize. In many cases, there will be more than one carcinoid tumor.
Colon lymphoma, or colonic lymphoma, is one of the relatively rare types of colon cancer, and it arises from the lymphatic system in the colon. Non-Hodgkin lymphoma is a more common form of colonic lymphoma.
These rare lesions in the colon occur due to the formation of abnormal cells in the tissues of the colon. The risk of gastrointestinal stromal tumors is increased by certain genetic factors. The symptoms of gastrointestinal stromal tumors include vomiting and blood in the stool. GISTs often begin as benign tumors and later become cancerous.
Leiomyosarcoma of the colon is an extremely invasive and rare tumor. The tumor develops in the muscularis propria, which is the smooth muscle layer of the gastrointestinal tract.
Melanomas of the colon are exceptionally rare. Melanoma is a type of skin cancer that can rarely metastasize into the colon. In exceedingly rare cases, melanoma-causing cancer cells (cancerous melanocytes) develop in the colon, and such cases are termed primary colonic melanoma.
Following are the colon cancer stages:
This stage is known as cancer in situ. The cancerous cells are present only in the inner lining of the colon, or mucosa.
Cancer develops in the mucosa and muscular layers of the colon. No cancer growth occurs in the nearby lymph nodes or tissues.
The cancer invades the wall of the colon, the muscle of the abdominal lining (visceral peritoneum), or the wall of the colon and nearby structures but does not spread to nearby lymph nodes.
The cancer has grown to the inner muscular lining with 1 to 3 lymph nodes, or the bowel wall or surrounding organs with 1 to 3 lymph nodes, or ≥ 4 lymph nodes, irrespective of the depth of cancer growth.
Cancer has spread to only one distant site, such as the lungs or liver, or to more than one distant site, or to the peritoneum, with or without invading distant organs.
Colon carcinoma occurs in the colon and is one of the most common cancers globally. There are various types of colon cancer. The most common are squamous cell carcinoma, lymphoma, adenocarcinoma, and carcinoid tumors.
Colon carcinoma is categorized into various stages depending on the extent of the disease’s spread. Early-stage cancers have a better prognosis than those in advanced stages.