What the diagnosis means
Most colorectal cancers are adenocarcinomas arising from polyps in the lining of the colon or rectum. Stage depends on how deeply the tumour has grown into the bowel wall, whether lymph nodes are involved, and whether it has spread — most often to the liver or lungs. Where the cancer sits matters: rectal cancer (the last part of the bowel) is treated differently from colon cancer because of the anatomy and the role of radiation.
Where medical oncology fits
Surgery is the main curative treatment for colon cancer; the colorectal surgeon removes the affected segment with its lymph nodes. Medical oncology adds chemotherapy after surgery for stage III and some higher-risk stage II cancers, leads treatment when the cancer has spread, and works with liver surgeons and interventional radiologists when metastases might be removed or ablated. For rectal cancer, radiation oncology and medical oncology often treat first — chemoradiation or "total neoadjuvant therapy" — to shrink the tumour before surgery and, in some cases, avoid it.
Tests that shape treatment
- MSI / mismatch-repair (MMR) status — cancers with deficient MMR (about one in seven) respond remarkably well to immunotherapy and may not benefit from some chemotherapy; testing also raises the question of Lynch syndrome in the family.
- RAS and BRAF mutations — decide whether anti-EGFR antibody drugs can be used in metastatic disease.
- CEA blood marker — useful for monitoring, not for diagnosis.
- Sidedness (right or left colon) also influences drug choice in advanced disease.
When systemic treatment is considered
- After surgery (adjuvant): 3–6 months of chemotherapy for stage III; discussed for higher-risk stage II.
- Rectal cancer before surgery: chemoradiation, often with additional chemotherapy, to improve the chance of complete removal and preserve function.
- Metastatic disease: chemotherapy combinations with targeted antibodies chosen by RAS/BRAF status; immunotherapy for MSI-high cancers; surgery or ablation of liver or lung metastases when feasible — a curative option for a minority, which is why the plan is discussed jointly with surgeons.
What to expect
Chemotherapy is usually given as 2-weekly or 3-weekly cycles, sometimes with a portable pump over 46 hours. Typical side effects include tiredness, nausea, diarrhoea, mouth soreness and — with oxaliplatin — sensitivity to cold and tingling in the fingers and toes, which is monitored so doses can be adjusted before it becomes permanent.
Questions to ask
- What is my stage, and do I need chemotherapy after surgery?
- Have MSI/MMR, RAS and BRAF tests been done?
- For rectal cancer: is treatment before surgery recommended, and could surgery be avoided?
- If the cancer has spread: is surgery for the metastases possible now or later?
- Should my family be tested for Lynch syndrome?
Preparing for your consultation
Bring the colonoscopy and biopsy reports, CT (and MRI for rectal cancer) with reports, surgical and pathology reports if surgery is done, CEA results, and details of any bowel symptoms, stoma, and other illnesses.