🔬 Colorectal Cancer

What is Colorectal Cancer?

Colorectal cancer refers to cancer that starts in the colon (large intestine) or the rectum (the final section of the large intestine). Together, these cancers are called colorectal cancer. They are among the most common cancers worldwide, and their rates are rising in the Philippines, partly due to changing diets and lifestyle factors.

The good news: colorectal cancer is one of the most preventable cancers when caught through regular screening, and it is highly treatable — especially when found early.

Types of Colorectal Cancer

Adenocarcinoma

The most common type, accounting for over 95% of colorectal cancers. It develops from the cells lining the inside of the colon or rectum.

Other Rare Types

These include carcinoid tumours, gastrointestinal stromal tumours (GISTs), lymphomas, and sarcomas — all much less common.

Symptoms

Colorectal cancer may not cause symptoms in its early stages. When symptoms appear, they can include:

• A change in bowel habits (diarrhoea, constipation, or narrowing of the stool) that lasts for more than a few days
• A feeling that the bowel doesn't empty completely
• Rectal bleeding or blood in the stool (bright red or very dark)
• Cramping or abdominal discomfort, gas, or pain
• Weakness and fatigue
• Unexplained weight loss
• Anaemia (low red blood cell count) — often causing fatigue and pallor

Screening: The Key to Prevention

Most colorectal cancers develop from polyps — small growths on the inner lining of the colon or rectum that are initially benign but can become cancerous over time. Regular screening can find and remove polyps before they turn into cancer.

Recommended screening methods include:

• Colonoscopy — The gold standard. A flexible tube with a camera is used to examine the entire colon. Polyps found can be removed during the procedure. Recommended every 10 years starting at age 45 for average-risk individuals.
• Stool tests — Including faecal occult blood test (FOBT) or faecal immunochemical test (FIT). Annual testing recommended.
• CT Colonography (Virtual Colonoscopy) — Uses CT imaging to produce detailed pictures of the colon.

Diagnosis and Staging

After diagnosis by colonoscopy/biopsy, the following tests assess the extent of the cancer:

• CT scan of chest, abdomen, and pelvis
• MRI of the rectum (for rectal cancers)
• PET scan (in some cases)
• Blood tests including CEA (carcinoembryonic antigen) tumour marker
• Molecular/genetic testing — including MSI (microsatellite instability) and RAS/BRAF mutation testing to guide treatment

Colorectal cancer is staged from Stage I to Stage IV:

• Stage I: Cancer confined to the inner layers of the colon wall. Surgery is usually curative.
• Stage II: Cancer has grown through the colon wall but not into nearby lymph nodes.
• Stage III: Cancer has spread to nearby lymph nodes. Chemotherapy after surgery significantly reduces recurrence risk.
• Stage IV: Cancer has spread to distant organs, most commonly the liver and lungs. Treatment is complex but many patients achieve long-term disease control.

Treatment Options

Surgery

The primary treatment for most stages. Options include colectomy (removal of part or all of the colon), anterior resection (for rectal cancer), and laparoscopic (minimally invasive) techniques. Some patients may temporarily or permanently require a colostomy (external bag for waste).

Chemotherapy

Standard regimens include FOLFOX (folinic acid + fluorouracil + oxaliplatin) and FOLFIRI. Chemotherapy is used before surgery to shrink tumours, after surgery to reduce recurrence risk, and for metastatic disease.

Radiation Therapy

More commonly used for rectal cancer than colon cancer. Often given before surgery (neoadjuvant) to shrink the tumour and reduce the risk of local recurrence.

Targeted Therapy

For metastatic colorectal cancer, drugs such as bevacizumab (Avastin), cetuximab, and panitumumab can be added to chemotherapy depending on the tumour's genetic profile (RAS/BRAF status).

Immunotherapy

Patients whose tumours are MSI-high (microsatellite instable) or MMR-deficient respond well to immune checkpoint inhibitors such as pembrolizumab and nivolumab — even without chemotherapy.

Liver Metastasis Treatment

When colorectal cancer spreads to the liver, it may still be treatable. Options include surgical resection of liver metastases, ablation (RFA, microwave), TACE, or SIRT (Selective Internal Radiation Therapy) with Y-90 microspheres.