GI: Colorectal polyps and cancer Flashcards
What is the most common type of colonic cancer?
Adenocarcinoma - with variably differentiated glandular epithelium with mucin production
Two main tyoes are: Tubular and Villous
(rest are neuroendocrine (release serotonin) and rarely primary lymphoma)
Describe the adenoma-carcinoma sequence
Normal epithelium
Small adenoma (polyp)
Large adenoma/polyp
Invasive adenocarcinoma (occurs in around 10%)
Metastases
This process can take 10-15 years
What proportion of presentation of colorectal cancer are over the age of 60?
86%
What are predisposing factors to the development of colorectal carcinoma?
-
85% are sporadic with no gamilai/genetic influence. RF:
- Age >40
- Male
- Inflammatory bowel disease
- Previous adenoma/CRC/Neoplastic polyps
-
Environmental influences
- Diet - reduced fibre, low calcium, increased red meat
- Alcohol
- Smoking
- Physical inactivity
- Obesity
-
Genetic predisposition
- HNPCC
- FAP
What dietary factors can increase the risk of developing colon cancer?
- Low-fibre
- High red and processed meat content
What genetic problems can predispose to the development of colorectal cancer?
- Familial adenomatous polyposis (FAP)
- Hereditary non-polyposis colon cancer (HNPCC; Lynch syndrome)
- Peutz-Jeghers syndrome
What is familial adenomatous polyposis?
An autosomal dominant condition arising from germline mutations of the APC gene located on chromosome 5q21-q22 (tumour supressor gene)
What is the penetrance of FAP?
Virtually 100%
What are the main characteristic findings in FAP?
Presence of hundreds to thousands of colorectal and duodenal adenomas (excess growth of adenomatous tissue). High risk of amlaignant change in early adulhood.
What is the average age of developing colon cancer from FAP?
39
Screening in FAP
Annual colonscopy from 10-12 years
What should people affected with FAP be offered?
Prophylactic colectomy before the age of 20
What surgical options are available for treating FAP?
- Colectomy + Ileorectal anastamosis
- Restorative proctocolectomy or pouch procedure with complete removal of rectal mucosa.
What is the commonest cause of death in colectomised patients with FAP?
Duodenal adenomas which progress to cancer
What is hereditary non-polyposis colon cancer?
Autosomal dominant
A disease caused by a mutation in one of the DNA mismatch repair genes, usually hMSH2 or hMLH1 but others (hMSH6, PMS1 and PMS) have been reported.
The defect in function causes naturally occurring highly repeated short DNA sequences known as microsatellites to be shorter or longer than normal, a phenomenon called microsatellite instability (MSI).
Where do tumours in HNPCC tend to occur?
Right colon
Typical onset of CRC in HNPCC
<10 years
Screening in HNPCC
Biennial colonscopy from age 25
What is the lifetime risk of developing cancer if you have HNPCC?
70-80%
What cancers (other than colon cancer) are common in HNPCC?
- Endometrial (COMMONEST)
- Stomach
- Small intestine
- Pancreas
- Bladder
- Skin
- Brain
- Hepatobiliary
What symptoms might someone with colorectal cancer have?
-
Change in bowel habit
- Rectal bleeding
- Diarrhoea
- Tenesmus
- Tiredness
- Weight loss/anorexia
- Abdominal pain (colicky)
- Iron deficiency anaemia
What features might indicate someone has a colorectal cancer in the left side of their colon?
- PR Exam - bleeding/mucus, Mass
- Altered bowel habits/Obstruction
- Tenesmus
- Mass in the L iliac fossa/PR on exam
What features might suggest a colorectal cancer is on the right side of the colon/caecum?
Often asymptomatic
- Iron deficiency Anaemia
- Abdominal pain
- Obstruction less likely
- Occult bleeding
- Mass in R iliac fossa
What features can occur in either left or ride sided colon cancer?
- Abdominal mass
- Signs of perforation
- Signs of haemorrhage
- Signs of fistula formation
Differentials of colorectal cancer
-
Inflammatory bowel disease
- Average onset younger (40-60), typically presents with diarrhoea continuing blood/mucous
-
Haemorrhoids
- Bright red rectal bleeding on stool - rarely presents with abdo discomfort, weight loss, altered bowel habits
-
Diverticulitis
- Can present with blood in stool and changed bowel habit but likely to have systemic signs of inflammation
Refer for immediate investigation of bowel cancer if
>40 with unexplained weight loss and abdo pain
>50 unexplained rectal bleeding
>60 iron defieincy anaemia or changes in bowel habit
+ve occult faecal blood test
What type of bowel habit change most commonly occurs in colon cancer?
Diarrhoea, although can have constipation if obstructed
Where does colorectal cancer most commonly spread?
- Liver
- Lungs
- Brain
- Bone
What is the pathology of colorectal cancer?
Polypoid mass with ulceration, which directly infiltrates through the bowel wall
What investigations might you consider doing in someone with suspected colorectal cancer?
- Faecal occult blood test
- Sigmoidoscopy/colonoscopy
- Bloods - FBC (microcytic), LFT (liver mets), Raised CEA (not diagnostic due to poor specifity but should be monitored for disease progression)
-
Imaging
-
Radiology
- CT colonography
- Barium enema
- CT abdo pelvis
- Liver MRI/US
- PET scan
-
Endoscopy
- COLONOSCOPY AND BIOPSY (flexible sigmoidoscopy if comorbidities/intolerance)
-
Radiology
- Consider DNA test if FAP
What is faecal occult blood testing used for?
Mass population screeing
(Screening = FOBT, colonoscopy)
What might FBC show in someone with colorectal cancer?
Iron deficiency anaemia
What might LFTs show in someone with colorectal cancer?
Deranged if liver mets present