Colorectal carcinoma

Question 1

How common is colorectal cancer?

Who does it affect (age/gender)?

Answer 1

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

Question 2

What are the risk factors of colorectal cancer?

Answer 2

1. Increasing age
2. Family hx of colon cancer or colon polyps
3. Sugar consumption
4. Colorectal neoplastic polyps
5. Animal fat (saturated); red meat consumption; low fibre
6. Chronic IBD
7. Obesity
8. Smoking
9. Alcohol
10. Previous cancer
11. Genetic predisposition i.e HNPCC/FAP

*Hereditary non-polyposis colorectal cancer (Lynch syndrome) ; Familial adenomatous polyposis

Question 3

Which factors reduce the risk of colorectal cancer?

Answer 3

1. Vegetables
2. Garlic
3. Milk
4. Calcium consumption
5. Exercise (colon only)
6. Aspirin & other NSAIDs

Question 4

Normal mucosa => adenoma => invasive cancer

Answer 4

How a colorectal cancer progresses

Question 5

Genetics of colorectal cancer:

Explain chromosomal instability.

Answer 5

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).

Question 6

Genetics of colorectal cancer:

Explain CpG island methylator phenotype (CIMP).

Answer 6

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.

Question 7

Genetics of colorectal cancer:

Explain Micro-satellite instability.

Answer 7

Microsatellite instability tumours common in proximal colon.

They arise from defective DNA repair through inactivation of mis-match repair gene.

Question 8

How does colorectal cancer spread?

Answer 8

Colorectal cancer is a polypoid mass with ulceration.

Spreads by direct infiltration through the bowel wall.

Followed by lymphatics, blood, transcoelomic

Question 9

What are the most common sites of metastases for colorectal cancer?

Answer 9

Lungs, liver, bone

Question 10

Describe the histology of colorectal cancer.

Answer 10

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)

Question 11

What are the clinical features of right-sided and left-sided colorectal cancer?

Answer 11

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

Question 12

How do you examine the patient?

Answer 12

Digital exam and GI exam

Question 13

What are the diagnostic investigations for colorectal cancer?

Answer 13

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

Question 14

What is the management for colorectal cancer?

Answer 14

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

Question 15

What is total mesorectal excision (TME) used for?

Answer 15

Rectal cancers where it removes the entire mesorectal tissue surrounding the cancer.

TME + radiotherapy reduces rates of local recurrences of rectal cancer

Question 16

What technique is used for cancers anywhere in the colon (apart from rectum)?

Answer 16

Segmental resection and restorative anastomosis, with removal of the draining lymph nodes as far as the root of the mesentery.

Question 17

What is local transanal endoscopic surgery used for?

Answer 17

Superficial localised rectal cancers

Question 18

Why is radiotherapy not useful in in colonic cancers proximal to the rectum?

Answer 18

Difficulties delivering sufficient dose to the tumour without being toxic to nearby healthy tissue

Question 19

Which screening tools are available for colorectal cancer?

Answer 19

UK National bowel cancer screening program (>55years):

1. FOB (faecal occult blood test) or FIT (faecal immunochemical test) => FOB is less sensitive therefore is not used as commonly as FIT
2. Flexible sigmoidoscopy
3. GOLD STANDARD : Colonoscopy

Question 20

What are the investigations carried out for suspected colorectal cancer?

Answer 20

FBC (microcytic anaemia)
FOB test 
Flexible sigmoidoscopy or colonoscopy
LFT
Liver MRI/US

Question 21

Which staging method is used for colorectal cancer?

Answer 21

TNM now preferred to Duke’s staging criteria

Question 22

What is Hartmann’s procedure?

Answer 22

Surgical resection of the recto-sigmoid colon, closure of the anorectal stump and formation of an end colostomy.

Used in emergency bowel obstruction, perforation, palliation

Question 23

What is the prognosis of colorectal cancers?

Answer 23

Depends on age and stage - stage 1 of disease 5yr survival is ~75% but stage 4 is 5% survival