Bowel cancer, also known as colorectal cancer, is a malignant disease affecting the colon or rectum, which are parts of the large intestine. It is one of the most common cancers worldwide and a leading cause of cancer-related mortality, particularly in developed nations (Sung et al., 2021). In the United Kingdom, bowel cancer is the fourth most common cancer and the second leading cause of cancer death (Cancer Research UK, 2023). This article explores the causes, symptoms, and treatment options for bowel cancer, supported by textbooks, peer-reviewed journal articles and reputable health organisations.
1.0 Overview of Bowel Cancer
The large intestine is responsible for absorbing water and electrolytes and forming faeces. Bowel cancer typically develops from adenomatous polyps, which are benign growths arising from the mucosal lining of the colon or rectum. Over time, some polyps may undergo malignant transformation through accumulation of genetic mutations (Kumar, Abbas and Aster, 2020).
The majority of bowel cancers are adenocarcinomas, originating from glandular epithelial cells. The disease progression often follows the adenoma–carcinoma sequence, a well-established model describing stepwise genetic changes such as mutations in the APC, KRAS, and TP53 genes (Fearon and Vogelstein, 1990).
2.0 Causes and Risk Factors
The exact cause of bowel cancer is multifactorial, involving a combination of genetic predisposition, environmental influences, and lifestyle factors.
2.1 Age
Age is the most significant risk factor. The incidence rises markedly after the age of 50 (Rawla, Sunkara and Barsouk, 2019). This is likely due to cumulative genetic mutations and prolonged exposure to environmental carcinogens.
2.2 Genetic Factors and Family History
Approximately 5–10% of bowel cancers are due to inherited syndromes. The most notable are:
- Lynch syndrome (Hereditary Non-Polyposis Colorectal Cancer)
- Familial Adenomatous Polyposis (FAP)
Lynch syndrome results from mutations in DNA mismatch repair genes, leading to microsatellite instability (Boland and Goel, 2010). Individuals with FAP develop hundreds of polyps and have nearly a 100% lifetime risk if untreated (Kumar et al., 2020).
A family history of bowel cancer also significantly increases risk.
2.3 Diet and Lifestyle
Dietary habits strongly influence risk. High consumption of processed meat and red meat has been associated with increased incidence (World Cancer Research Fund, 2018). In contrast, diets rich in fibre, fruits and vegetables appear protective.
Other lifestyle-related risk factors include:
- Obesity
- Physical inactivity
- Smoking
- Excessive alcohol consumption
For example, a sedentary lifestyle combined with a high-fat, low-fibre diet increases colonic transit time, potentially prolonging mucosal exposure to carcinogens.
2.4 Inflammatory Bowel Disease
Chronic inflammatory conditions such as ulcerative colitis and Crohn’s disease increase colorectal cancer risk due to persistent mucosal inflammation and dysplasia (McCance and Huether, 2019).
3.0 Pathophysiology
Bowel cancer develops through accumulation of genetic and epigenetic alterations that disrupt normal cell regulation. The adenoma–carcinoma sequence involves progressive mutations leading to uncontrolled proliferation, resistance to apoptosis and angiogenesis (Fearon and Vogelstein, 1990).
Tumours may invade through the bowel wall and metastasise via lymphatic and haematogenous routes, commonly spreading to the liver, lungs, and peritoneum. Liver metastasis occurs because venous drainage from the colon passes through the portal circulation.
4.0 Symptoms
Symptoms vary depending on tumour location and stage. Early-stage bowel cancer may be asymptomatic, which underscores the importance of screening.
4.1 Changes in Bowel Habit
- Persistent diarrhoea or constipation
- Feeling of incomplete evacuation
- Narrow stools
These symptoms are particularly common in left-sided colon or rectal cancers.
4.2 Rectal Bleeding
Blood in the stool is a common symptom. It may appear bright red or darker, depending on tumour location. This symptom is sometimes mistakenly attributed to haemorrhoids.
4.3 Abdominal Pain and Bloating
Tumours may cause partial obstruction, leading to colicky abdominal pain and distension.
4.4 Unexplained Weight Loss and Fatigue
Chronic blood loss may result in iron-deficiency anaemia, causing fatigue and pallor.
4.5 Symptoms of Advanced Disease
In advanced cases, patients may experience:
- Jaundice (due to liver metastases)
- Severe bowel obstruction
- Palpable abdominal mass
For example, a 62-year-old patient presenting with fatigue and microcytic anaemia on blood tests may later be diagnosed with right-sided colon cancer following colonoscopy.
5.0 Diagnosis
5.1 Screening
In the UK, the NHS Bowel Cancer Screening Programme offers faecal immunochemical testing (FIT) to adults aged 50–74 (NHS, 2023). Screening reduces mortality through early detection (Atkin et al., 2010).
5.2 Colonoscopy
Colonoscopy is the gold standard diagnostic procedure, allowing visualisation and biopsy of suspicious lesions.
5.3 Imaging
CT scans assess staging and detect metastases. MRI is particularly useful for rectal cancer staging.
6.0 Treatment
Treatment depends on tumour stage, location and patient fitness.
6.1 Surgery
Surgical resection is the primary treatment for localised disease. The affected segment of bowel and regional lymph nodes are removed (Townsend et al., 2021).
For rectal cancer, total mesorectal excision improves local control.
6.2 Chemotherapy
Adjuvant chemotherapy reduces recurrence risk in stage III and high-risk stage II disease. Common regimens include FOLFOX (fluorouracil, leucovorin and oxaliplatin) (Dekker et al., 2019).
In metastatic disease, chemotherapy may be combined with targeted agents such as bevacizumab.
6.3 Radiotherapy
Radiotherapy is particularly important in rectal cancer, where pre-operative (neoadjuvant) treatment can shrink tumours and reduce recurrence.
6.4 Targeted Therapy and Immunotherapy
Advances in molecular profiling have enabled targeted treatment strategies. Tumours with microsatellite instability (MSI-high) respond well to immunotherapy agents such as pembrolizumab (Dekker et al., 2019).
6.5 Palliative Care
For advanced disease, palliative interventions aim to relieve symptoms and improve quality of life.
7.0 Prognosis
Prognosis depends on stage at diagnosis. According to global statistics, five-year survival exceeds 90% for early-stage disease but falls significantly in metastatic cases (Sung et al., 2021). Early detection through screening is therefore crucial.
8.0 Prevention and Public Health Strategies
Preventive strategies include:
- Maintaining a healthy body weight
- Engaging in regular physical activity
- Reducing consumption of processed meat
- Increasing dietary fibre intake
- Participating in screening programmes
Public health initiatives emphasise lifestyle modification and early diagnosis to reduce mortality.
Bowel cancer is a common and potentially fatal malignancy arising from the colon or rectum. Its development involves a complex interplay of genetic mutations, lifestyle factors, and chronic inflammation. While early disease may present with subtle or no symptoms, advanced cancer can cause significant morbidity. Management strategies range from surgical resection to chemotherapy, radiotherapy and targeted therapies. Early detection through screening and awareness of symptoms significantly improve survival outcomes.
References
Atkin, W.S., Edwards, R., Kralj-Hans, I. et al. (2010) ‘Once-only flexible sigmoidoscopy screening in prevention of colorectal cancer’, The Lancet, 375(9726), pp. 1624–1633.
Boland, C.R. and Goel, A. (2010) ‘Microsatellite instability in colorectal cancer’, Gastroenterology, 138(6), pp. 2073–2087.
Cancer Research UK (2023) Bowel cancer statistics. Available at: https://www.cancerresearchuk.org.
Dekker, E., Tanis, P.J., Vleugels, J.L.A. et al. (2019) ‘Colorectal cancer’, The Lancet, 394(10207), pp. 1467–1480.
Fearon, E.R. and Vogelstein, B. (1990) ‘A genetic model for colorectal tumorigenesis’, Cell, 61(5), pp. 759–767.
Kumar, V., Abbas, A.K. and Aster, J.C. (2020) Robbins and Cotran Pathologic Basis of Disease. 10th edn. Philadelphia: Elsevier.
McCance, K.L. and Huether, S.E. (2019) Pathophysiology: The Biologic Basis for Disease in Adults and Children. 8th edn. St Louis: Elsevier.
NHS (2023) Bowel cancer screening. Available at: https://www.nhs.uk.
Rawla, P., Sunkara, T. and Barsouk, A. (2019) ‘Epidemiology of colorectal cancer’, Przeglad Gastroenterologiczny, 14(2), pp. 89–103.
Sung, H., Ferlay, J., Siegel, R.L. et al. (2021) ‘Global cancer statistics 2020’, CA: A Cancer Journal for Clinicians, 71(3), pp. 209–249.
Townsend, C.M., Beauchamp, R.D., Evers, B.M. and Mattox, K.L. (2021) Sabiston Textbook of Surgery. 21st edn. Philadelphia: Elsevier.
