Pathology of Colorectal Carcinoma

Question 1

What is a polyp?

Answer 1

Protrusion/tumour above an epithelial surface but it does not indicate the cause, nor whether it is benign or malignant

Question 2

Types of polyps?

Answer 2

Most polyps are benign:

Epithelial - these are the most common, spec. neoplastic

Mesenchymal - lipomas, etc

Malignant:

(Adeno)carcinomas - malignancy of epithelial cells

Lymphoma

GIST (mesenchymal)

Question 3

Differential diagnosis of a colonic polyp?

Answer 3

1. Adenoma
2. Serrated polyp
3. Polypoid carcinoma
4. Other

To differentiate, histopathology is required

Question 4

3 types of polyps, in relation to macroscopic appearance?

Answer 4

Pedunculated (hanging from a stalk)

Sessile (carpet-like and derived blood supply from several places)

Flat (barely protrude)

Flat polyps are the most difficult to remove

Question 5

Histopathology of an adenoma?

Answer 5

DYSPLASTIC epithelial lining (benign polyp)

Not invasive and do not metastasise; but they are pre-malignant (precursors of adenocarcinoma)

Question 6

3 morphological varieties of adenoma?

Answer 6

Tubular - contains tubular crypts; rounded and often attached to the bowel wall by a definite stalk

Villous (less common) - small bowel-like villous surface; flatter and larger

Tubulovillous - features of both

Question 7

Adenoma-carcinoma sequence?

Answer 7

1. Normal epithelium - mutations are collected in the stem cells, e.g: usually the APC gene is hit first
2. Small adenoma (dysplastic) acquire mutations in K-ras and c-yes to form a large adenoma
3. Large adenoma acquires mutations in important genes, e.g: p53
4. Adenocarcinoma (invasive) develops

Note: not all colorectal adenomas have the same molecular genetic origins

Question 8

How are adenomas removed?

Answer 8

They must all be removed, as they are pre-malignant

Endoscopically or surgically

Question 9

Treatment of adenocarcinoma?

Answer 9

Surgical, in most cases, and colon/rectum is removed and sent to pathology for staging

Question 10

Why do many colorectal tumours grow towards the mesentary?

Answer 10

For the good blood supply

Question 11

Staging of colorectal carcinoma?

Answer 11

Dukes staging predicts the prognosis:

Dukes A - confined by muscularis propria

Dukes B - through muscularis propria

Dukes C - metastatic to lymph nodes

Prognosis worsens from A-C

Question 12

Locations of colorectal carcinomas?

Answer 12

75% left sided (rectum, sigmoid, descending) - symptoms inc. blood in stool, altered bowel habits and obstruction

25% are right-sided (caecum is expandable and ascending) - symptoms inc. anaemia (haemorrhage) and weight loss

Question 13

Gross and histopathological appearances of colorectal carcinoma?

Answer 13

Varied gross appearance - polypoid, stricturing, ulcerating

Typical histopathological appearance - adenocarcinomas

Question 14

Patterns of spread of colorectal carcinoma?

Answer 14

Local invasion to mesorectum, peritoneum and other organs

Lymphatic spread to mesenteric nodes

Haematogenous (to the liver and distant sites)

Question 15

What are 2 inherited cancer syndromes?

Answer 15

Hereditary non-polyposis coli (HNPCC)/lynch syndrome; autosomal dominant and due to a defect in DNA mismatch repair (MLH-1, MSH-2, PMS-1 or MSH-6). Tends to be late onset

Familial Adenomatous Polyposis (FAP); autosomal dominant and due to a defect in a tumour suppressor gene (APC gene); tends to be early onset

Question 16

Characteristics of HNPCC?

Answer 16

Right-sided tumours with <100 polyps; there is a Crohn’s-like inflammatory response and there are mucinous tumours

There is an assoc. with gastric and endometrial carcinoma

Question 17

Characteristics of FAP?

Answer 17

Occurs throughout the colon with >100 polyps; they are adenocarcinoma NOS (non-specific)

There is no specific inflammatory response but there is an assoc. with desmoid tumours and thyroid carcinoma