Colorectal Cancer

Colorectal cancer (CRC) arises from the epithelial lining of the large intestine, often following the 'adenoma-carcinoma sequence.' Risk factors include increasing age, high red/processed meat intake, obesity, smoking, and family history. Hereditary syndromes like Lynch Syndrome (HNPCC) and Familial Adenomatous Polyposis (FAP) carry a very high risk. Left-sided cancers typically present with altered bowel habit (diarrhoea/constipation) and rectal bleeding, while right-sided (caecal) cancers often present with occult bleeding and iron-deficiency anaemia. In the UK, the Bowel Cancer Screening Programme offers FIT (Faecal Immunochemical Test) kits every 2 years to individuals aged 60-74 (expanding to 50+). Under the 2-week-wait (2WW) pathway, NICE mandates urgent referral for patients with persistent rectal bleeding, unexplained weight loss, or change in bowel habit. Colonoscopy is the primary diagnostic tool; if a lesion is found, CT Chest, Abdomen, and Pelvis (CAP) is used for staging (TNM). Pelvic MRI is specific for staging rectal cancers. Management focus is curative surgical resection (e.g., right hemicolectomy, anterior resection) where possible, with adjuvant chemotherapy (e.g., 5-FU/Oxaliplatin) for Higher-risk Stage II or Stage III disease.

The 'Adenoma-Carcinoma Sequence' describes the progression from normal mucosa to dysplastic polyp to invasive cancer through the accumulation of genetic mutations. It typically involves: 1. Loss of the APC tumour suppressor gene (causing polyp formation), 2. Activation of the K-ras oncogene, and 3. Loss of the p53 tumour suppressor gene. Lynch Syndrome involves germline mutations in mismatch repair genes (MLH1, MSH2, MSH6, PMS2), leading to microsatellite instability. CRC most commonly metastasizes to the liver via the portal venous system, followed by the lungs. Rectal cancer can spread directly via the middle and inferior rectal veins to the IVC, potentially bypassing the liver.

NICE NG12 Referral Criteria (2-week wait): 1. Age 40+ with unexplained weight loss AND abdominal pain. 2. Age 50+ with unexplained rectal bleeding. 3. Age 60+ with iron deficiency anaemia OR changes in bowel habit. 4. Positive FIT test result. Examination may reveal a palpable mass (RIF for caecal cancer), hepatomegaly (metastases), or a mass on digital rectal examination (DRE). Rectal cancer specifically may present with 'tenesmus'—the constant feeling of needing to pass stools. Complications include large bowel obstruction (requiring emergency surgery or stenting) and perforation.

Bedside: DRE, FIT test (if screening). Bloods: FBC (microcytic anaemia), LFTs (checking for liver mets), CEA (baseline for follow-up). Diagnostic Gold Standard: Colonoscopy and Biopsy. If colonoscopy is impossible (e.g. frail patient), CT Colonography (Virtual Colonoscopy) is an alternative. Staging: CT Chest/Abdomen/Pelvis (TNM staging). Specific for rectal cancer: Pelvic MRI and Endoluminal Ultrasound (to assess local invasion and nodal status).

MDT involvement is essential. Surgery: Right hemicolectomy (caecal/ascending colon), Left hemicolectomy (descending colon), Sigmoid colectomy, Anterior Resection (high rectal), or Abdominoperineal Resection (low rectal involving the sphincter, requires permanent colostomy). Medical: Adjuvant chemotherapy (e.g., FOLFOX) for Stage III (node-positive) disease. Radiotherapy: Used primarily in rectal cancer (pre-operatively to 'downstage' or post-operatively) to reduce local recurrence. Palliative: Stenting, bypass surgery, or palliative chemotherapy.