Colorectal cancer

Colorectal cancer (CRC), also known as bowel cancer, colon cancer, or rectal cancer, is the development of cancer from the colon or rectum, parts of the large intestine. It often starts as a benign tumour or polyp that becomes cancerous over time. The disease is more common in developed countries and affects men more than women.

Signs and Symptoms

The symptoms of colorectal cancer depend on the tumour's location in the bowel and whether it has metastasized. Classic warning signs include blood in the stool, changes in bowel habits, unintentional weight loss, abdominal pain, fatigue, and nausea or vomiting. Rectal bleeding and anaemia are high-risk symptoms in people over 50. Notably, around 50% of colorectal cancer cases are asymptomatic.

Causes and Risk Factors

Most colorectal cancers (75-95%) occur in individuals with little or no genetic risk. Key risk factors include older age, male sex, high intake of fat, sugar, alcohol, red meat, processed meats, obesity, smoking, and lack of physical exercise. Inflammatory bowel diseases like Crohn's disease and ulcerative colitis also increase the risk. Genetic syndromes such as hereditary nonpolyposis colorectal cancer (Lynch syndrome) and familial adenomatous polyposis (FAP) are linked to higher rates of colorectal cancer but represent less than 5% of cases.

Diagnosis

Diagnosis typically involves a tissue biopsy obtained during a sigmoidoscopy or colonoscopy, followed by medical imaging to check for disease spread. CT scans, MRI, and PET scans may be used to determine the extent of metastasis.

Histopathological examination confirms the diagnosis, with most cases being adenocarcinomas. The TNM staging system is used to evaluate the cancer's progression, based on tumour size, lymph node involvement, and metastasis.

Prevention

Preventative measures include regular screening from ages 45 to 75, increased physical activity, a diet high in fibre, and reduced consumption of red and processed meats. Screening methods include colonoscopy, faecal occult blood testing (FOBT), and flexible sigmoidoscopy. Aspirin and other non-steroidal anti-inflammatory drugs may reduce risk, but their general use is not recommended due to potential side effects.

Treatment

Treatment varies depending on the cancer stage and may involve surgery, chemotherapy, radiation therapy, and targeted therapy. Early-stage colorectal cancer can often be cured with surgery, while advanced cases may require a combination of treatments to manage symptoms and improve quality of life.

Surgery

Surgical options include partial colectomy, proctocolectomy, and, in some cases, removal of liver or lung metastases. Minimally invasive techniques like laparoscopic surgery are preferred when feasible.

Chemotherapy

Chemotherapy is used in stages III and IV, often in combination with drugs like fluorouracil, capecitabine, and oxaliplatin. It may be given before surgery to shrink tumours or after surgery to eliminate remaining cancer cells.

Radiation Therapy

Radiation therapy is primarily used for rectal cancer, often in combination with chemotherapy. It helps shrink tumours before surgery and reduce recurrence rates.

Immunotherapy

Immune checkpoint inhibitors, such as pembrolizumab, are useful for colorectal cancers with mismatch repair deficiency. These treatments help the immune system recognise and attack cancer cells.

Palliative Care

For advanced colorectal cancer, palliative care focuses on symptom relief and improving quality of life. Surgical and non-surgical options, including radiation and pain management, are employed to manage complications and maintain comfort.

Prognosis

The five-year survival rate for colorectal cancer in the U.S. is approximately 65%, varying by stage and individual health. Early detection significantly improves survival rates. However, the prognosis for advanced metastatic disease is generally poor. Recurrence rates and survival also depend on factors like lymph node involvement and tumour grade.

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Self-assessment MCQs (single best answer)

Which of the following is NOT a common symptom of colorectal cancer?

What percentage of colorectal cancer cases are asymptomatic?

Which of the following is a key risk factor for colorectal cancer?

Which diagnostic method is typically used to confirm colorectal cancer?

What is the primary purpose of a colonoscopy in the context of colorectal cancer?

Which stage of colorectal cancer is characterised by metastasis to distant organs?

Which of the following is NOT a recommended preventive measure for colorectal cancer?

Which type of treatment is primarily used for rectal cancer and helps shrink tumours before surgery?

What is the five-year survival rate for colorectal cancer in the U.S.?

Which genetic syndrome is linked to a higher rate of colorectal cancer but represents less than 5% of cases?