Colorectal Cancer Flashcards
what are the risk factors for colorectal cancer?
> most are sporadic
10% familial risk
CRC syndromes
inflammatory bowel disease (1%)
what are the risk factors for sporadic cases?
> age
male (significant)
previous adenoma/CRC
Environmental influences
what environmental influences affect risk of sporadic cases of colorectal cancer?
> diet: low fibre, low fruit + veg, low calcium, high reed meat, high alcohol > obesity > lack of exercise > smoking > diabetes mellitus
what are colorectal polyps?
> protuberant growths > variety of histological types > epithelial or mesenchymal > benign or malignant > can develop into colorectal cancer
are adenomas benign?
yes
what tissue does an adenoma originate from?
epithelial
what are the 2 main histological types of adenomas?
> tubular
villous
(>indeterminate tubulovillous)
what are the different morphological types of adenomas?
> pedunculated
> sessile
what factors mean adenoma lesions are high risk?
> size
number
degree of dysplasia
villous architecture
what is the molecular sequence that leads to development of a carcinoma from an adenoma?
> oncogene activation, k-ras, c-myc
tumour suppressor gene lost (APC, p53, DCC)
defective DNA repair pathway gene (microsatellite instability)
All this leads to cell proliferation and apotosis.
what is the presentation of colorectal cancer?
> rectal bleeding
altered bowel opening (diarrhoea)
Iron deficiency anaemia in men and non-menstruating women)
palpable rectal or right lower abdominal mass
acute colonic obstruction (stenosing tumour)
systemic symptoms (weight loss, anorexia)
when are presenting symptoms investigated?
> each symptom on its own, investigated if age >60yrs
> combined symptoms, investigated if age > 40 yrs
what sort of colonic malignancy is likely with iron deficiency anaemia?
right sided colonic malignancy
why is colonoscopy investigation of choice?
tissue biopsies can be taken and therapy can be delivered (polypectomy)
what radiological imaging is available for investigating colorectal cancer?
> barium enema
CT colonography
(> CT abdo/pelvis)
what investigations are used for staging colorectal cancer?
> CT scan chest/abdomen/pelvis
MRI scan for rectal tumours
PET scan/rectal endoscopic ultrasound in selected cases
describe dukes classification of cancer
A: tumour confined to the mucosa
B: tumour extended through mucosa to muscle layer
C: involvement of lymph nodes
D: distal metastatic spread
what treatment may Dukes A or cancer polyps require?
endoscopic or local resection
what does the operative procedure depend on?
> site
size
stage
can a patient with a single metastasis be operated on?
yes if you resect the metastasis as well
what is chemotherapy used for in colorectal cancer?
> palliation
adjuvant
Dukes c, and b?
to mop up micro metastasis
what is used for palliation in advanced disease?
chemotherapy and colonic stenting to prevent colonic obstruction
what is radiotherapy used for?
> rectal cancer only
> as neoadjuvant therapy
what is the prognosis for dukes stage a?
5 year survival 83%
what is the prognosis for dukes stage b?
5 year survival 64%
what is the prognosis for dukes stage c?
5 yr survival 38%
what is the prognosis for dukes stage d?
5 yr survival 3%
what is the aim of population screening?
> detect pre-malignant adenomas/early cancers in the general population
what are the modalities for population screening in colorectal cancer?
> faecal occult blood test > faecal immunochemical test > flexible sigmoidoscopy > colonoscopy > ct colonoscopy
what is carried out if the FOBT is positive?
colonoscopy
what age group is screened in the FOBT screening program?
50-74 year olds, every 2 years
what percentage decrease in the risk of colorectal cancer mortality does the FOBT bring about?
a 15% reduction
what high risk groups are screened for colorectal cancer?
> heritable conditions: FAP, HNPCC
inflammatory bowel disease
familial risk
previous adenomas/ colorectal cancer
is FAP dominant or recessive?
dominant
what are the effects of FAP?
> multiple adenomas throughout the colon (50%15yrs, 95% by 35 yrs)
high risk of malignant change in early adulthood, by age 40 if untreated
how often are patients with FAP screened?
> annually from age 10/12
what is usually provided as prophylaxis to patients with FAP at ages 16-25?
prophylactic proctocolectomy
what extra colonic manifestations can occur with FAP?
> benign gastric fundic cystic hyperplastic
duodenal adenomas (in 90% with periampullary cancer)
congenial retinal hypertrophy of pigment epithelia
desmoid tumours
what is used in FAP to reduce polyp number and prevent recurrence of high grade adenomas?
NSAID chemoprevention
is HNPCC an autosomal recessive condition?
no it is autosomal dominant
what is the mutation in HNPCC?
in the DNA mismatch repair genes (MMR)
what do tumours in HNPCC typically have?
a molecular characteristic called microsatellite instability, frequent mutations in short repeated DNA sequences
An early onset right sided colorectal cancer that is associated with other cancers (endometrial, genitourinary, stomach, pancreas) is associated with what condition?
HNPCC
how do you diagnose HNPCC?
clinical criteria (Amsterdam/bathesda and genetic testing
how often to patients with HNPCC receive a screening colonoscopy?
every 2 years
describe screening in patients with a high moderate risk from a family history of CRC
5 yearly colonoscopy from age 50 yrs
what is surveillance colonoscopy dependent on in IBD?
10 years post diagnosis: duration, extent and activity of inflammation and presence of dysplasia
patient with previous CRC have a colonoscopy how frequently?
every 5 years
what does screening in patients with previous adenomas depend on?
the number of polyps, size, degree of dysplasia
