Colon Cancer

Colon cancer is a malignant epithelial tumour arising between the caecum and rectosigmoid junction, with adenocarcinoma accounting for the great majority. Spread occurs by direct invasion, regional lymphatics, portal venous dissemination to the liver, systemic haematogenous spread and transperitoneal implantation.

Management is stage driven. Localised disease is primarily surgical. Node positive disease requires adjuvant systemic therapy. Metastatic disease requires assessment of both tumour biology and whether all metastatic disease can potentially be resected.

All newly diagnosed colorectal cancers should undergo tumour mismatch repair or microsatellite instability assessment because this identifies Lynch syndrome candidates and materially changes systemic treatment.

Right sided cancers commonly present with occult bleeding, iron deficiency anaemia, fatigue and weight loss.

Left sided cancers more often produce altered bowel habit, progressive constipation, visible rectal bleeding, abdominal distension or obstruction.

Advanced disease may present with liver metastases, ascites, perforation or malignant large bowel obstruction.

A new iron deficiency anaemia in an adult, particularly a man or postmenopausal woman, requires colorectal investigation even without gastrointestinal symptoms.

Colonoscopy with biopsy: establish histology and assess the remainder of the colon for synchronous lesions.

CT chest, abdomen and pelvis with IV contrast: standard staging for distant metastatic disease.

Obtain baseline carcinoembryonic antigen before definitive treatment. It is useful for prognosis and postoperative surveillance but is not sufficiently sensitive or specific to diagnose colon cancer.

Complete colon evaluation before surgery whenever possible. If an obstructing tumour prevents full colonoscopy, evaluate the remaining colon after decompression or within the postoperative surveillance pathway.

Surgery

Curative resection removes the tumour bearing bowel and its lymphovascular drainage as one intact oncological specimen.

Aim for approximately 5 to 7 cm proximal and distal bowel margins, together with mesenteric division at the relevant named feeding vessels. At least 12 lymph nodes should be examined for reliable node negative staging.

Use minimally invasive colectomy when oncologically appropriate and technically feasible.

Locally invasive T4 tumours adherent to another organ should undergo en bloc resection rather than separation of the adhesion because the adherence may represent malignant invasion.

Adjuvant treatment

Stage I disease does not require adjuvant chemotherapy after complete resection.

Most stage II disease is treated with surgery alone. Consider chemotherapy with T4 tumour, perforation, obstruction, lymphovascular or perineural invasion, poor differentiation, inadequate nodal assessment or other adverse features.

Stage II mismatch repair deficient or microsatellite instability high cancer generally has a favourable prognosis and should not routinely receive fluoropyrimidine monotherapy.

Stage III disease requires oxaliplatin based adjuvant chemotherapy. FOLFOX is a reference regimen.

Modified FOLFOX6 every 14 days:

• Oxaliplatin 85 mg/m² IV day 1
• Leucovorin 400 mg/m² IV day 1
• Fluorouracil 400 mg/m² IV bolus day 1
• Fluorouracil 2400 mg/m² continuous IV infusion over 46 hours

CAPOX every 21 days:

• Oxaliplatin 130 mg/m² IV day 1
• Capecitabine 1000 mg/m² orally twice daily, days 1 to 14

For low risk stage III disease, T1 to T3 N1, three months of CAPOX is reasonable. T4 or N2 disease generally warrants six months of oxaliplatin based treatment when tolerated. Shorter treatment substantially reduces cumulative neuropathy.

Metastatic disease

Potentially resectable liver or lung metastases should be reviewed for curative metastasectomy rather than automatically considered palliative.

Advanced disease should undergo molecular testing including extended RAS, BRAF and mismatch repair or microsatellite instability status, with HER2 and other actionable alterations assessed where appropriate.

Systemic treatment is then selected according to tumour sidedness, molecular profile, disease burden and resectability.

Do not routinely resect an asymptomatic primary colon cancer in a patient with unresectable metastatic disease unless obstruction, perforation, bleeding or another local complication requires intervention.