Colorectal cancer

Question 1

types of colon cancer?

Answer 1

It is currently thought there are three types of colon cancer:

• sporadic (95%)
• hereditary non-polyposis colorectal carcinoma (HNPCC, 5%)
• familial adenomatous polyposis (FAP, <1%)

Question 2

Cause of sporadic colon cancer

Answer 2

Studies have shown that sporadic colon cancer may be due to a series of genetic mutations. For example, more than half of colon cancers show allelic loss of the APC gene. It is believed a further series of gene abnormalities e.g. activation of the K-ras oncogene, deletion of p53 and DCC tumour suppressor genes lead to invasive carcinoma.

Question 3

Causes of HNPCC (Lynch syndrome)

Answer 3

autosomal dominant condition, is themost common form of inherited colon cancer.Around 90% of patients develop cancers, often of the proximal colon, which are usually poorly differentiated and highly aggressive. Currently seven mutations have been identified, which affect genes involved in DNA mismatch repair leading to microsatellite instability. The mostcommon genes involvedare:

• MSH2 (60% of cases)
• MLH1 (30%)

Question 4

Patients with HNPCC (lynch syndrome) are also at higher risk of other cancers e.g.?

Answer 4

Endometrial cancer next most common association, after colon cancer

Question 5

Which criteria is sometimes used to aid diagnosis?

Answer 5

The Amsterdam criteria are sometimes used to aid diagnosis:

• at least 3 family members with colon cancer
• the cases span at least two generations
• at least one case diagnosed before the age of 50 years

Question 6

What is familial adenomatous polyposis (FAP)?

Answer 6

rare autosomal dominant condition which leads to the formation of hundreds of polyps by the age of 30-40 years. patients inevitably develop carcinoma

it is due to a mutation in a tumour suppressor gene caused adenomatous polyposis coli gene (APC), located on chromosome 5

genetic testing can be done by analysing DNA from a patient’s white cell

Question 7

treatment for FAP?

Answer 7

patients generally have a total colectomy with ileo-anal pouch formation in their twenties

Question 8

What is the most common type of inherited colorectal cancer

Answer 8

Hereditary non-polyposis colorectal carcinoma