Rectal vs Colon Cancer: Key Differences

Colon and rectal cancer are both types of colorectal cancer but develop in different parts of the large intestine. Colon cancer occurs in the upper sections, while rectal cancer forms in the final segment before the anus. These differences influence how each type is diagnosed, treated, and managed. This article explores key distinctions between rectal and colon cancer and what they mean for patients.

How Rectal and Colon Cancer Differ

While both rectal and colon cancer originate in the large intestine, their differences affect how symptoms appear, how they spread, and which treatment strategies are most effective. Recognising these distinctions helps guide treatment decisions.

Where Do Colon and Rectal Cancer Develop?

Colon Cancer: Develops in the colon, which is the longest portion of the large intestine. The colon absorbs water and nutrients from digested food while forming stool. Tumours can form in any part of the colon, with symptoms and treatment varying depending on location.

Rectal Cancer: Occurs in the rectum, the final segment of the large intestine that connects to the anus. The rectum stores stool before it is expelled from the body. Due to its limited space and proximity to other organs, rectal cancer presents unique challenges in treatment and surgical planning.

Symptoms

Colon Cancer: Symptoms include persistent diarrhoea, constipation, bloating, abdominal discomfort, and unexplained weight loss. Blood in the stool may appear dark or tarry due to digestion as it travels through the colon. Fatigue and anaemia are also common in advanced cases.

Rectal Cancer: Symptoms often include bright red blood in the stool, a feeling of incomplete bowel emptying, and changes in stool shape, such as narrow or ribbon-like stools. Rectal pain, urgency in bowel movements, and discomfort while sitting can also occur, particularly in later stages.

Risk Factors

Colon Cancer: Risk increases with age, particularly after 50. A diet high in processed meats, obesity, smoking, alcohol consumption, and a sedentary lifestyle contribute to higher risk. A family history of colorectal cancer or inflammatory bowel disease (IBD) can also increase susceptibility.

Rectal Cancer: While many of the same risk factors apply, rectal cancer has a slightly stronger association with hereditary conditions such as Lynch syndrome and familial adenomatous polyposis (FAP). Long-term inflammation from conditions like ulcerative colitis also raises the risk.

Diagnosis

Colon Cancer: Diagnosis is typically made through colonoscopy with a biopsy, blood tests (such as carcinoembryonic antigen [CEA] levels), and imaging like CT or MRI scans. These tests help assess the extent of the disease and its potential spread.

Rectal Cancer: In addition to colonoscopy and biopsy, rectal cancer often requires MRI or endorectal ultrasound to evaluate how deep the tumour has grown into surrounding tissues. This information is necessary for planning treatment, especially surgery.

Treatment 

Colon Cancer: Surgery is the primary treatment. Early-stage colon cancer is often treated with a colectomy, where the affected portion of the colon is removed. In more advanced cases, chemotherapy may be recommended before or after surgery. Radiation therapy is rarely used, except when tumours are located near the rectum.

Rectal Cancer: Due to the tight space of the pelvis, treatment is often more involved. Pre-operative radiation therapy (chemoradiation) is commonly used to shrink tumours before surgery, reducing the risk of recurrence. Surgery may involve a low anterior resection (LAR), preserving bowel function, or an abdominoperineal resection (APR), which may require a permanent colostomy if the anal sphincter cannot be preserved.

Risk of Cancer Spread

Colon Cancer: More likely to spread to the liver through the portal vein system, as the colon drains blood into this region. Lung metastases can also occur in later stages.

Rectal Cancer: More likely to spread to the lungs, as the rectum has a different blood supply. Liver metastases are also common, but lung involvement occurs more frequently compared to colon cancer.

Outlook and Survival Chances

Colon Cancer: When detected early (before spreading), the five-year survival rate is over 90%. If the cancer has spread to distant organs, survival rates decline, but treatment can still help control the disease.

Rectal Cancer: Early-stage rectal cancer has a similar survival rate to colon cancer, but there is a higher risk of local recurrence. Due to the confined space in the pelvis, complete tumour removal is more challenging, and post-treatment bowel dysfunction is more common.

When to Seek Medical Advice

If you experience persistent digestive symptoms, a medical evaluation is recommended. Signs that require attention include rectal bleeding, unexplained weight loss, ongoing changes in bowel habits, severe abdominal pain, and chronic fatigue. Early detection significantly improves treatment outcomes, so consulting a doctor if symptoms persist is advised.

Conclusion

While rectal and colon cancer share similarities, their differences in location, symptoms, treatment, and recovery mean they require distinct approaches. Rectal cancer often involves more complex treatment due to its confined space and proximity to pelvic organs, while colon cancer typically follows a more straightforward surgical path. Recognising these differences can help with early detection and informed decision-making.

Schedule an appointment today to discuss screening options or any concerns about your digestive health.