Colorectal Cancer

Overview

Colon cancer is the second most commonly diagnosed cancer. 1/12 people will develop bowel cancer before the age of 85. However, there are Survival rates are increasing. Early bowel cancer is cured by surgery alone (screening is important!!). If untreated, or diagnosed when distance metastases are present, >98% pf patients die in <5 years.

Colon anatomy and Physiology

The colon is divided into:

• Caecum (appendix off this)
• Ascending colon
• Transverse colon
• Descending colon
• Sigmoid colon
• Rectum

The ascending and descending colon are retroperitoneal, these are immobile. The transverse is mobile and lies within the peritoneal cavity. The transverse colon is supported by the greater omentum superiorly and attaches to the posterior abdominal wall (in front of the retroperitoneal cavity) by the transverse mesocolon.

The transverse colon is attached to the greater curvature of the stomach and first part of the duodenum via the greater omentum. The sigmoid colon is also attached

Main features of large intestine structure:

• Complete layer of circular smooth muscle throughout, but incomplete bands of longitudinal muscle (taeniae coli) in colon (stops at the rectum)
• Fatty appendages along taeniae (appendices epiploicae)
• Folded internal mucosal appearances (haustrations)
• ‘Segmented’ external appearances (sacculations)

Blood supply – from superior and inferior mesenteric artery

• Superior mesenteric artery
  • Ileocolic artery – last terminal ilealloop, caecum
  • Right colic artery – ascending colon
  • Middle colic artery – transverse colon up to the splenic flexure
• Inferior mesenteric artery
  • Left colic – splenic flexure and descending colon.
  • Sigmoid artery – sigmoid colon
  • Superior rectal artery – rectum and upper anal canal

Autonomic nerve supply

• Sympathetic, mainly from greater splanchnic nerves via SMA and IMA plexuses.
• Parasympathetic, from vagus via SMA and IMA plexus from caecum to splenic flexure and from pelvic parasympathetics (S2, 3, 4) via hypogastric plexuses and retroperitoneal nerves from splenic flexure to upper anal canal

Risk Factors

Family and personal history are strong risk factors. Polyposis syndrome including FAP has a 100% chance of developing colon cancer.

Clinical Manifestation

Signs and symptoms vary depending on the location of the tumour. 20% of people present at emergency with obstruction of large bowel or perforation.

Clinical Examination

• Anaemia
• Palpable mass on abdominal examination
• Palpable nodular liver (metastasis)
• Pigmentation (Peutz-Jeghers syndrome)
  • Discrete black brown lesion on lips

Differential Diagnosis

For more information: Clinical Presentation of Per-rectal bleeding

Investigation

• Rectal examination
• FBC
• Faecal occult blood testing (not done if symptomatic)
• Tumour markers
• CT imaging
• Colonoscopy

Diagnosis Colon cancer is usually diagnosed with colonoscopy and biopsy (takes 1-2 days for pathology results).

Pathology

Colorectal cancer are primarily adenocarcinoma. Colon cancer can be polyploid, ulcerative, stenosing or infiltrative.

Pathophysiology

Staging and Management

Staging CT and PET scan are used for staging colon cancer. The staging system used is TNM which look at the primary tumour, regional lymph node involvement and metastasis. Duke’s staging looks at the 5 year survival rate and this is based on the layers/sites the tumours have invaded.

Duke’s staging (5 year survival rate)

• Stage A – Tumour is confined to bowel wall only (75-90%)
• Stage B – Tumour is through bowel wall (55-70%)
• Stage C – Tumour has spread through regional lymph nodes and has a 30% 5 year survival rate
• Stage D is where the tumour has metastasized has a 5% 5 year survival rate.

Management

• Surgical Resection
  • +/- Neoadjuvant Chemotherapy
• Chemotherapy
• Radiotherapy
• Palliative care

Surgery can be curative if done early with lymphadenectomy. Surgical removal of parts of the colon will depend on site of primary tumour(s). Chemoradiotherapy is also used, chemo agent primarily 5-flurouracil. Finally palliative care if surgery is not an option.

Complications and Prognosis

Complications

• Chemotherapy side effects
  • Bone marrow suppression
  • Nausea, diarrhoea, abdominal pain
  • Alopecia
  • Hand-foot Syndrome

• Oxaliplatin side effects
  • Neuropathy
  • Hepatotoxicity
  • Pulmonary fibrosis
• Surgical complications
  • Haemorrhage
  • Erectile dysfunction and/or bladder dysfunction (after rectal excision)

Prognosis (Based on Dukes) Criteria 5-year survival rates for colorectal cancer are:

• Stage I – 90%
• Stage II – 75%
• Stage III – 44% to 83%
• Stage IV – 8%

Prevention

Screening

• Genetic testing for those with hereditary conditions
• Faecal Occult blood test
• Colonoscopy?

Family Adenomatous Polyposis

Overview

• Autosomal dominant
• APC gene on chromosome 5q21
• Penetrance 100%
• Characterized by 100’s of colonic polyps
• Mean age 39

Other manifestations

• Periemullary polyps
• Congenital hypertrophy of retinal pigment epithelium
• Osteomas skill and mandible
• Dental abnormalities

Hereditary Non-Poyposis colorectal Cancer

Overview

• Also known as Lynch Syndrome
• Autosomal dominant
• 80% lifetime risk of developing colorectal cancer
• increased risk uterine, gastric, urinary tract, small bowel and brain cancer
• Defect in DNA mismatch repair cause microsatellite instability

Peutz-Jeghers Syndrome

Overview

• Characterized by the development of noncancerous growths called hamartomatous polyps in the gastrointestinal tract (particularly the stomach and intestines)
• Greatly increased risk of developing certain types of cancer
• Increases risk of small-bowel and pancreatic cancer, colorectal cancer and sex-cord tumours with annular tubules of the ovary
• Other clinical features often found in children and young adults: Perioral pigmentation, pigmentations of fingers

References

UpToDate
BestPractice
Oxford Handbook of Clinical Surgery
Toronto Notes 2016