Lower GI Flashcards
What is the most common type of neoplastic polyp of the lower GI tract
Adenoma
Invasion of what mucosal layer constitutes invasive adenocarcinoma of a colorectal polyp
The muscularis mucosae
Breach of the basement membrane is considered intramucosal carcinoma, with no metastatic potential because the colonic mucosa lacks functional lymphatic channels
What is the main risk factor for a colorectal polyp that correlates with risk of malignancy
Size of the polyp
What gene is mutated in familial adenomatous polyposis, and what pathway is affects
The APC gene (a tumour suppressor)
Part of the WnT signalling pathway. APC helps suppress B-catenin, preventing production of cell cycle proteins
What percentage of patients with familial adenomatous polyposis go on to get colorectal carcinoma
100%
What genes are mutated in hereditary non-polyposis colorectal cancer. What is the name of the associated syndrome
Mismatch repair genes
Lynch syndrome
What is the incidence pattern of malignancies of the small bowel
Adenocarcinoma = neuroendocrine
Lower incidence of lymphoma and sarcoma
Deficiency of what component of diet is thought to be associated with increased risk of colorectal cancer in western countries
Vegetable fibre, therefore less stool bulk.
What are the rates of KRAS mutation in colorectal adenocarcinoma
50%
In colorectal cancer MLH1 promoter methylation is associated with what mutation profile
BRAF mutation
KRAS, TP53 typically not mutated
What are common features of colorectal cancers with MSI/MMRd
Sessile polyps
Mucinous differentiation and peritumoral lymphocyte infiltration
Right side of colon
What are the typical microscopic features of colon adenocarcinoma
Tall columnar cells
Strong desmoplastic response
Gland formation (may be absent in poorly differentiated forms)
Mucin accumulation in intestinal wall associated with poorer prognosis
Signet ring cells uncommon
What are the two most important prognostic factors in colorectal carcinoma
Depth of invasion and presence of LN metastasis
Why does rectal carcinoma less commonly metastasise to the liver compared to colon cancer
The rectum does not have venous drainage via the portal system
What are the epithelial types of the anal canal
Upper third: rectal columnar epithelium
Middle third: transitional epithelium
Lower third: stratified squamous epithelium
