Carcinoma colon risk factors pathogenesis cilincalbfeactute diagnois and treatment
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"colorectal cancer"[MeSH Terms] AND "treatment"[MeSH Terms]
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"colorectal neoplasms"[MeSH Terms] AND "risk factors"[MeSH Terms]
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Carcinoma of the Colon (Colorectal Carcinoma)
1. Epidemiology
Colorectal cancer (CRC) is the second most common cause of cancer death in the UK (~42,000 new cases/year). About two-thirds arise in the colon and one-third in the rectum. It is more common in resource-rich countries and slightly more prevalent in men (56% vs 44%). The global incidence closely tracks dietary patterns, highlighting the dominant role of environmental factors.
- Bailey and Love's Short Practice of Surgery, 28th Ed.
2. Risk Factors
Non-modifiable
| Factor | Details |
|---|---|
| Age | Peak incidence after age 50; risk rises with age |
| Family history | 1st-degree relative with CRC doubles risk |
| FAP (Familial Adenomatous Polyposis) | APC gene mutation (chr 5q); lifetime CRC risk approaches 100% by age 50 |
| Lynch syndrome (HNPCC) | Mismatch repair (MMR) gene mutations (MLH1, MSH2, etc.); 70-80% lifetime risk |
| Inflammatory bowel disease | Both ulcerative colitis and Crohn's disease increase risk |
| Prior colorectal polyps or cancer | Adenomatous polyps are precursors |
Modifiable
| Factor | Details |
|---|---|
| Red/processed meat | Haem iron and N-nitroso compounds are carcinogenic |
| Low dietary fibre | Longer mucosal exposure to dietary carcinogens |
| Obesity and sedentary lifestyle | Increased risk |
| Smoking and alcohol | Both independently increase risk |
| Cholecystectomy | Marginally increases risk of right-sided colon cancer |
Protective Factors
- High fibre intake, calcium and magnesium
- Aspirin and NSAIDs - substantial epidemiological evidence for protection via prostaglandin inhibition
- Physical activity
- Colonic microbiota diversity
Recent 2025 meta-analysis (PMID: 40210826) confirmed red and processed meat consumption is significantly associated with CRC risk in prospective studies. A 2025 systematic review (PMID: 40010692) further confirmed dietary patterns as major modifiable risk factors via the CUP Global programme.
3. Pathogenesis
The Adenoma-Carcinoma Sequence
The dominant model: normal mucosa → hyperproliferative epithelium → adenoma → invasive carcinoma. This sequence is supported by:
- Similar left-sided distribution of adenomas and cancers (~70%)
- Adenomas found in one-third of CRC resection specimens
- Cancer incidence falls in screening programmes using colonoscopy + polypectomy
Bailey and Love's, p. 1380
Three Major Molecular Pathways
| Pathway | Early Events | Progressive Events | Clinical Notes |
|---|---|---|---|
| APC / Chromosomal Instability | APC gene mutation (somatic or inherited) | KRAS mutation → P53 mutation → DCC mutation | Conventional adenoma-to-carcinoma sequence (most common) |
| MMR / Microsatellite Instability | MMR gene mutation (inherited in Lynch, sporadic methylation) | KRAS, PIK3CA mutations | HNPCC/Lynch syndrome; sporadic right-sided tumours |
| CpG Island Methylator (CIMP/Serrated) | BRAF V600E mutation + MMR promoter methylation | Epigenetic silencing of tumour suppressor genes | Serrated adenoma-associated carcinoma |
Quick Compendium of Clinical Pathology, 5th Ed., p. 403
Key Genetic Events
- APC gene (chr 5q): mutated in ~67% of colonic adenomas - an early event
- KRAS: activates cell signalling; found in larger lesions - a later event
- p53: mutated in carcinomas but not adenomas - marker of invasion
- MSI (microsatellite instability): feature of Lynch syndrome, also occurs sporadically (especially right-sided)
Consensus Molecular Subtypes (CMS)
International bioinformatic classification of >4000 patients identified four subtypes:
- CMS1: MSI, immune activation (right-sided)
- CMS2: WNT/MYC signalling activation
- CMS3: Metabolic dysregulation
- CMS4: TGF-beta activation (worst prognosis)
4. Clinical Features
Symptoms (vary by tumour location)
| Right-sided colon (caecum, ascending) | Left-sided colon (sigmoid, descending) |
|---|---|
| Occult blood loss → iron-deficiency anaemia | Change in bowel habit (constipation / loose stools) |
| Vague abdominal discomfort | Rectal bleeding (bright red or dark) |
| Palpable right iliac fossa mass | Tenesmus |
| Constitutional: weight loss, fatigue | Colicky abdominal pain |
| Often presents late (large lumen) | Bowel obstruction (smaller lumen) |
Complications at Presentation
- Obstruction (more common left-sided)
- Perforation - peritonitis
- Fistula formation (colovesical, colovaginal)
- Haemorrhage
Examination Findings
- Abdominal mass (right > left)
- Signs of anaemia (pallor)
- Hepatomegaly (liver metastases)
- Digital rectal examination: may detect rectal involvement
- Virchow's node (left supraclavicular lymphadenopathy) - distant spread
Dukes' Classification (historical but still used)
| Stage | Description |
|---|---|
| A | Limited to bowel wall |
| B | Through bowel wall, no nodes |
| C | Lymph node involvement |
| D | Distant metastases |
5. Diagnosis
Blood Tests
- FBC: iron-deficiency anaemia (especially right-sided)
- LFTs: liver metastases
- CEA (carcinoembryonic antigen): not diagnostic, but used for monitoring response to treatment and detecting recurrence. Elevated CEA pre-op = worse prognosis
Endoscopy
- Colonoscopy: gold standard - allows visualisation, biopsy, and simultaneous polypectomy. Required for the entire colon
- Flexible sigmoidoscopy: for left-sided lesions; used in screening
- CT colonography (virtual colonoscopy): alternative if endoscopy incomplete or contraindicated
Radiology (Staging)
- CT chest/abdomen/pelvis: primary staging modality - assesses local invasion, lymph nodes, distant metastases (especially liver and lung)
- MRI: for rectal tumours - assesses mesorectal fascia, CRM (circumferential resection margin)
- PET-CT: for recurrent or metastatic disease
- Liver ultrasound/MRI: characterise hepatic lesions
Histopathology
- Biopsy via colonoscopy: confirms adenocarcinoma
- Tumour grade: well (G1), moderately (G2), poorly differentiated (G3)
- Molecular testing: KRAS/NRAS/BRAF/MMR status - mandatory for metastatic disease to guide therapy
TNM Staging (AJCC 8th Edition)
| T | Description |
|---|---|
| Tis | Carcinoma in situ (intramucosal) |
| T1 | Invades submucosa |
| T2 | Invades muscularis propria |
| T3 | Through muscularis propria into pericolorectal tissues |
| T4a | Invades visceral peritoneum |
| T4b | Invades/adheres to adjacent organs |
| N | Description |
|---|---|
| N0 | No nodes |
| N1 | 1-3 positive regional nodes |
| N2 | ≥4 positive regional nodes |
| M | Description |
|---|---|
| M0 | No distant metastases |
| M1a | One distant site/organ |
| M1b | Two or more distant sites/organs |
| M1c | Peritoneal metastases |
Schwartz's Principles of Surgery, 11th Ed.
6. Treatment
Surgery (primary treatment)
- Right hemicolectomy: caecum, ascending, hepatic flexure tumours
- Extended right hemicolectomy: transverse colon
- Left hemicolectomy: descending colon
- Sigmoid colectomy: sigmoid colon
- Anterior resection: upper rectum
- Hartmann's procedure: emergency left-sided obstruction/perforation
- Total colectomy: FAP, synchronous tumours, UC-associated CRC
Principles: Wide resection with adequate margins + en bloc lymphadenectomy (minimum 12 nodes required for accurate staging). Laparoscopic approach is standard for elective cases - equivalent oncological outcomes, faster recovery.
Adjuvant Chemotherapy
| Stage | Recommendation |
|---|---|
| Stage I | Surgery alone; no adjuvant chemo |
| Stage II (low risk) | Surgery alone (controversial; consider if high-risk features) |
| Stage II (high risk) | Consider FOLFOX or capecitabine (high-risk features: T4, perforation, <12 nodes, PNI, LVI) |
| Stage III | FOLFOX (oxaliplatin + 5-FU + leucovorin) or CAPOX x 6 months - standard of care |
| Stage IV | Systemic chemotherapy +/- targeted therapy |
Chemotherapy Regimens (Metastatic / Stage IV)
- FOLFOX: 5-FU + leucovorin + oxaliplatin
- FOLFIRI: 5-FU + leucovorin + irinotecan
- CAPOX/XELOX: capecitabine + oxaliplatin
Targeted / Biological Therapy
| Agent | Target | Indication |
|---|---|---|
| Bevacizumab (Avastin) | Anti-VEGF | Metastatic CRC, with chemo |
| Cetuximab (Erbitux) | Anti-EGFR (monoclonal Ab) | Metastatic CRC - RAS wild type only |
| Panitumumab | Anti-EGFR (monoclonal Ab) | Metastatic CRC - RAS wild type only |
| Pembrolizumab / Nivolumab | Anti-PD-1 (immune checkpoint) | MSI-H / dMMR metastatic CRC |
| Encorafenib + cetuximab | BRAF V600E + EGFR | BRAF V600E mutant metastatic CRC |
Critical: KRAS/NRAS mutation = resistance to anti-EGFR agents; these must be tested before prescribing cetuximab or panitumumab.
Bailey and Love's, p. 217; Quick Compendium of Clinical Pathology, 5th Ed.
Treatment of Hereditary CRC (FAP)
- Total proctocolectomy with ileal pouch-anal anastomosis (IPAA) - procedure of choice
- Alternative: total abdominal colectomy with ileorectal anastomosis (requires rectal surveillance)
- COX-2 inhibitors (celecoxib, sulindac) may slow polyp development
Metastatic Disease
- Liver metastases: hepatic resection if technically feasible offers potential cure (5-year survival ~35-40%)
- Peritoneal metastases: cytoreductive surgery + HIPEC in selected patients
- Lung metastases: metastasectomy in selected cases
Screening (Prevention)
- Average risk: colonoscopy every 10 years from age 50 (or FIT/gFOBT annually)
- High risk (FAP family): flexible sigmoidoscopy from age 10-15 years; genetic testing
- Lynch syndrome family: colonoscopy every 1-2 years from age 25
Summary
| Aspect | Key Points |
|---|---|
| Commonest type | Adenocarcinoma (>95%) |
| Precursor | Adenomatous polyp (adenoma-carcinoma sequence) |
| Key gene | APC (early), KRAS (intermediate), p53 (late) |
| Presentation | Right: anaemia; Left: bleeding/obstruction |
| Staging | TNM / Dukes' |
| Curative treatment | Surgery (hemicolectomy) |
| Stage III adjuvant | FOLFOX chemotherapy |
| Metastatic targeted | Anti-EGFR only if RAS wild-type; anti-PD1 if MSI-H |
Sources: Bailey and Love's Short Practice of Surgery (28th Ed.) | Schwartz's Principles of Surgery (11th Ed.) | Quick Compendium of Clinical Pathology (5th Ed.) | Recent PubMed evidence (PMIDs: 40210826, 40010692)
Make a presentation comparing surgical approaches for different CRC locations
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The presentation is ready. Here's your download link:
CRC Surgical Approaches
Presentation · PPTX
What's inside (8 slides, dark navy + surgical red/blue theme):
| Slide | Content |
|---|---|
| 1 | Title slide - with the Schwartz's colon anatomy diagram |
| 2 | Master overview table - all CRC locations, operations, vessels ligated, and anastomosis type |
| 3 | Right-sided CRC - Ileocaecectomy, Right Hemicolectomy, Extended Right Hemicolectomy (with anatomy diagram) |
| 4 | Left-sided CRC - Transverse Colectomy, Left Hemicolectomy, Sigmoid Colectomy (with anatomy diagram) |
| 5 | Rectal cancer - Local excision/TEM, Anterior Resection, Abdominoperineal Resection, Hartmann's Procedure |
| 6 | Special cases - Total/Subtotal Colectomy, IPAA for FAP; Laparoscopic vs Open comparison table |
| 7 | General surgical principles - 6 principles: margins, lymphadenectomy, TME, vascular ligation, tension-free anastomosis, endoscopic options |
| 8 | Quick-reference summary - visual horizontal flow (caecum → rectum → operation) + 4 regional rule cards |
All content sourced from Schwartz's Principles of Surgery (11th Ed.), Bailey & Love (28th Ed.), and Yamada's Gastroenterology (7th Ed.).
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