What is Colon Cancer?

Colon cancer, also known as colorectal cancer (CRC) when including the rectum, is one of the most common cancers worldwide and a leading cause of cancer-related deaths. According to the Indian Council of Medical Research (ICMR), colon cancer accounts for about 4–5% of all cancers in India, with a rising trend in both urban and rural regions due to lifestyle changes 1. It is most often diagnosed in individuals above the age of 50, though younger cases are increasingly being reported 4.

What is Colon Cancer?

Colon cancer is a growth of cells that begins in a part of the large intestine called the colon. The colon is the first and longest part of the large intestine. The large intestine is the last part of the digestive system. The digestive system breaks down food for the body to use6.

Colon cancer typically affects older adults, though it can happen at any age. It usually begins as small clumps of cells called polyps that form inside the colon. Polyps generally aren't cancerous, but some can turn into colon cancers over time.

Polyps often don't cause symptoms. For this reason, doctors recommend regular screening tests to look for polyps in the colon. Detecting and removing polyps helps prevent colon cancer(3,4,6).

Types of Colon Cancer 4

Most colon cancers are adenocarcinomas, which develop from the glandular cells lining the colon 4. Other, less common types include:

• Mucinous adenocarcinoma: Produces mucus within the tumour.
• Signet ring cell carcinoma: A rare, aggressive type with cells that look like signet rings under a microscope.
• Small cell and squamous cell carcinoma: Very rare subtypes.

Stages of Colon Cancer

According to the American Joint Committee on Cancer (AJCC), the AJCC TNM system (8th Edition) is the most widely used staging system for colon cancer 2. It combines information about the tumour (T) how deeply it has grown into the colon wall, whether it has spread to nearby lymph nodes (N), and if it has metastasized to distant organs (M). Numbers or letters after T, N, and M provide more details about each of these factors, with higher numbers indicating more advanced disease.

Once the T, N, and M categories have been determined, they are combined in a process called ‘staging’ to arrive at an overall stage group, described by Roman numerals from Stage I to Stage IV (2,3).

Colon cancer is broadly staged as follows(2,3,4):

• Stage 0: Cancer is limited to the innermost layer (mucosa) of the colon.
• Stage I: Cancer has grown into the submucosa or muscle layer but has not spread to lymph nodes.
• Stage II: Cancer has invaded through the muscle into nearby tissues but has not reached lymph nodes.
• Stage III: Cancer has spread to nearby lymph nodes but not to distant organs.
• Stage IV: Cancer has spread (metastasized) to distant organs such as the liver, lungs, or peritoneum.

Other systems such as the Dukes’ classification and Astler-Coller modification were historically used to describe the extent of colon cancer, but are now largely replaced by the AJCC TNM staging system 2.

Causes of Colon Cancer(4,5,6).

While the exact cause is unknown, colon cancer usually results from genetic mutations that alter normal cell growth Certain risk factors increase the likelihood of developing colon cancer:

• Age above 50 years
• Family history of colorectal cancer or polyps
• Inflammatory bowel disease (IBD) such as ulcerative colitis or Crohn’s disease
• Low-fiber, high-fat diet
• Sedentary lifestyle and obesity
• Smoking and alcohol consumption
• Inherited syndromes like Familial Adenomatous Polyposis (FAP) or Lynch syndrome.

Symptoms of Colon Cancer 4

Symptoms may vary depending on the tumour’s location and stage. Early stages may not cause noticeable symptoms. Common signs include:

• Change in bowel habits (diarrhoea, constipation, or narrow stools)
• Blood in stool or black/tarry stools
• Abdominal pain, cramping, or bloating
• Unexplained weight loss or fatigue
• A feeling of incomplete bowel movement
• Weakness or anaemia due to blood loss

Screening and Diagnosis (3,4,6)

Colon cancer is one of the few cancers where screening can actually prevent the disease.

Common screening and diagnostic methods include:

• Colonoscopy: Direct visualization and biopsy of the colon.
• Fecal occult blood test (FOBT) or Fecal immunochemical test (FIT): Detect hidden blood in stool.
• CT colonography (Virtual colonoscopy): Imaging to view the colon interior.
• Biopsy: Confirms the diagnosis under a microscope.
• CT, MRI, or PET-CT scans: Assess the stage and possible metastasis.
• CEA (Carcinoembryonic Antigen) test: A tumour marker used for monitoring.

Treatment (3,4,5)

If colon cancer develops, many treatments can help control it. Treatments include surgery, radiation therapy and medicines, such as chemotherapy, targeted therapy and immunotherapy.Once diagnosed, a multidisciplinary team comprising of Gastrointestinal Oncologists, Surgical Oncologists, Medical Oncologists, and Radiation Oncologists will determine the most appropriate treatment based on the stage and patient’s overall health.

1. Surgery

• Polypectomy / Local excision: For very early cancers.
• Colectomy (Partial or Total): Removal of part or all of the colon, often with nearby lymph nodes.
• Laparoscopic or robotic surgery: Minimally invasive approaches with faster recovery.

2. Chemotherapy

Commonly used drugs include 5-Fluorouracil (5-FU), Capecitabine, Oxaliplatin, and Irinotecan.

Given after surgery (adjuvant) to kill residual cancer cells or before surgery (neoadjuvant) in locally advanced cases.

3. Targeted Therapy

Drugs such as Bevacizumab, Cetuximab, and Panitumumab target specific pathways that help cancer cells grow.

4. Immunotherapy

Used in advanced or microsatellite instability-high (MSI-H) tumours with agents like Pembrolizumab and Nivolumab.

5. Radiation Therapy

More commonly used for rectal cancers, but may be used selectively for colon cancer to control local spread or pain relief.

6. Supportive and Palliative Care

Nutritional counseling, pain management, and psychosocial support are vital parts of treatment and recovery.

Survival Rate (3,4)

The prognosis of colon cancer depends on the stage at diagnosis, grade, patient’s overall health, and response to treatment.

• Stage I and II: 5-year survival rate up to 90% if detected early.
• Stage III: Around 65–70%.
• Stage IV: Drops to around 15–20%, but newer therapies are improving outcomes.

Early detection through regular screening greatly improves survival and quality of life.

References

1. Indian Council of Medical Research (ICMR) – National Cancer Registry Programme (NCRP), 2023
2. AJCC Cancer Staging Manual, 8th Edition (2017) – Colon and Rectum Chapter
3. National Comprehensive Cancer Network (NCCN) Guidelines: Colon Cancer v1.2025
4. American Cancer Society – Colon and Rectal Cancer: Causes, Stages, and Treatment (2024 update)
5. Cancer Research UK – Bowel (Colon) Cancer Overview and Treatment Options
6. https://www.mayoclinic.org/diseases-conditions/colon-cancer/symptoms-causes/syc-20353669