Colorectal carcinoma Flashcards
How common is colorectal cancer?
Who does it affect (age/gender)?
3rd most common cancer worldwide
2nd most common cause of cancer death in UK
Incidence increases with age ; avg age of diagnosis 60-65yrs
Men>women
What are the risk factors of colorectal cancer?
- Increasing age
- Family hx of colon cancer or colon polyps
- Sugar consumption
- Colorectal neoplastic polyps
- Animal fat (saturated); red meat consumption; low fibre
- Chronic IBD
- Obesity
- Smoking
- Alcohol
- Previous cancer
- Genetic predisposition i.e HNPCC/FAP
*Hereditary non-polyposis colorectal cancer (Lynch syndrome) ; Familial adenomatous polyposis
Which factors reduce the risk of colorectal cancer?
- Vegetables
- Garlic
- Milk
- Calcium consumption
- Exercise (colon only)
- Aspirin & other NSAIDs
Normal mucosa => adenoma => invasive cancer
How a colorectal cancer progresses
Genetics of colorectal cancer:
Explain chromosomal instability.
Chromosomal instability: the most common cause of adenomas in the colon.
Mutation in tumour suppressor genes, initiated by a mutation in gene coding adenomatous polyposis coli (APC).
Genetics of colorectal cancer:
Explain CpG island methylator phenotype (CIMP).
CIMP tumours arise via the serrated neoplasia pathway in proximal colon.
Initial mutation in BRAF/KRAS - progress via epigenetic silencing of tumour suppressor and mis-match repair genes by promoting methylation.
Genetics of colorectal cancer:
Explain Micro-satellite instability.
Microsatellite instability tumours common in proximal colon.
They arise from defective DNA repair through inactivation of mis-match repair gene.
How does colorectal cancer spread?
Colorectal cancer is a polypoid mass with ulceration.
Spreads by direct infiltration through the bowel wall.
Followed by lymphatics, blood, transcoelomic
What are the most common sites of metastases for colorectal cancer?
Lungs, liver, bone
Describe the histology of colorectal cancer.
Adenocarcinoma with variably differentiated glandular epithelium & mucin production.
Signet rings cells - mucin displaces the nucleus to the side of the cell (uncommon but poor prognosis)
What are the clinical features of right-sided and left-sided colorectal cancer?
Left-sided colon: Bleeding/mucus PR Altered bowel habit or obstruction Looser, more frequent stool Tenesmus (need to empty bowels, with little to no stool passed) Rectal mass
Right-sided colon: Weight loss Low Hb (symptoms of anaemia: fatigue, lethargy etc) Abdominal pain Obstruction less likely
Either: Abdominal mass Perforation Haemorrhage Fistula
Cancers arising in caecum or right colon often asymptomatic until they present with iron deficiency anaemia.
Cancer may present with bowel obstruction
How do you examine the patient?
Digital exam and GI exam
What are the diagnostic investigations for colorectal cancer?
Gold standard: colonoscopy + biopsy for histology
Double contrast barium enema - visualise the large bowel (now superseded by CT)
CT - chest, abdo and pelvic. Tumour size, local spread, liver & lung metastases for tumour staging
PET scan - occult metastases + for suspicious lesions on CT or MRI
Endoanal ultrasound & pelvic MRI - staging rectal cancer
What is the management for colorectal cancer?
Long-term survival = cancer completely cleared by surgery with adequate clearance margins and regional lymph node clearance.
Usually laparoscopic surgery.
Right hemicolectomy: caecal, ascending and proximal transverse colon tumours
Left hemicolectomy: distal transverse, descending tumours
Sigmoid colectomy for sigmoid tumours
Anterior resection: low sigmoid or high rectal tumours
Abdomino-perineal resection: low rectal tumours(<8cm from anus) => permanent colostomy and removal of rectum & anus
What is total mesorectal excision (TME) used for?
Rectal cancers where it removes the entire mesorectal tissue surrounding the cancer.
TME + radiotherapy reduces rates of local recurrences of rectal cancer