Colorectal Cancer Treatment: Multimodal Options by Stage and Personalized Planning

Pre-Treatment Workup

• History, physical, DRE
• CEA baseline
• Staging: CT chest/abdomen/pelvis (+/- MRI rectum, PET-CT for equivocal mets)
• Colonoscopy with biopsy (if not done), tattooing
• MSI/MMR testing (all CRC) → Lynch screening, immunotherapy eligibility
• RAS/BRAF, HER2, NTRK for metastatic (guide targeted therapy)
• Germline testing if <50, family history, MSI-H

Treatment by Stage

Stage I (T1–2, N0)

• Surgery alone (colectomy with lymphadenectomy).
• T1 with favorable features (well-diff, no LVI, negative margin) → local excision possible.
• 5-yr OS >90%.

Stage II (T3–4, N0)

• Surgery ± adjuvant chemo.
• High-risk features (T4, perforation, obstruction, <12 nodes, LVI/perineural, poor differentiation, MSI-H): discuss chemo (CAPOX/FOLFOX 3–6 mo).
• MSI-H: favorable prognosis; chemo benefit uncertain.

Stage III (Any T, N1–2)

• Surgery → adjuvant chemo (CAPOX 3 mo or FOLFOX 6 mo standard).
• Age/comorbidity: 3-mo CAPOX non-inferior with less neuropathy (IDEA collaboration).
• MSI-H: consider omission if low clinical risk (ongoing trials).

Stage IV (Metastatic)

• Resectable oligometastatic: conversion therapy → metastasectomy ± primary resection → adjuvant. 5-yr OS 30–50%.
• Unresectable: systemic therapy ± local therapy for symptom control.
  • Left RAS/BRAF WT: FOLFOX/FOLFIRI + anti-EGFR (cetuximab/panitumumab)
  • Right or RAS mut: FOLFOX/FOLFIRI + bevacizumab
  • MSI-H/dMMR: pembrolizumab 1L
  • HER2+: trastuzumab + tucatinib + chemo
  • NTRK fusion: larotrectinib/entrectinib
• Maintenance strategies (bevacizumab ± 5-FU/capecitabine) after induction.

Rectal Cancer (Stage II–III)

• Neoadjuvant: short-course RT (5×5 Gy) → surgery (TME) → adjuvant chemo (TOTAL neoadjuvant therapy [TNT] emerging: chemo + RT → surgery).
• Watch-and-wait for clinical complete response (cCR) after TNT (selected centers).

Supportive Care During Treatment

• Nausea: 5-HT3 + NK1 antagonist + dexamethasone
• Neuropathy: duloxetine (treatment); prevention unproven (calcium/magnesium, glutamine not standard)
• Diarrhea: loperamide, budesonide, dose modification
• Hand-foot syndrome: urea cream, dose hold
• Psychosocial: distress screening, navigation, support groups
• Financial: copay assistance, disability, clinical trial coverage

Survivorship

• Surveillance: CEA q3–6 mo × 5 yr; CT CAP q6–12 mo × 3–5 yr; colonoscopy at 1 yr, then 3 yr, then 5 yr.
• Manage late effects: neuropathy, LARS (low anterior resection syndrome), stoma issues, sexual dysfunction, fear of recurrence.
• Lifestyle: exercise, weight control, smoking cessation improve recurrence-free survival.

Prognosis

Stage-dependent: I 90%, II 70–85%, III 50–75%, IV 15–30% (improving with molecular selection). Early detection + multidisciplinary care = best outcomes.