Cancer colon

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• The peak incidence for colorectal carcinoma is

between ages 60 and 79. Fewer than 20% of cases

occur before age 50.

• When colorectal carcinoma is found in a young person,

pre-existing ulcerative colitis or one of the polyposis

syndromes must be suspected.

• Male-to-female ratio is 1.2:1.

• Colorectal carcinoma has a worldwide distribution,

with the highest death rates in the United States.

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* Risk factors for cancer colon:

1. Genetic predisposition.

2. Dietary factors.

3. Precancerous lesions:

– Colonic adenoma.

– Hereditary familial polyposis coli.

– Ulcerative colitis.

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• The dietary factors receiving the most attention as predisposing

to a higher incidence of cancer colon are:

A diet with high calories and low fibers is risky….

• Mechanism:

1. Reduced fiber content leads to decreased stool bulk, increased

fecal transit time in the bowel, and an altered bacterial flora of the

intestine. Potentially toxic oxidative byproducts of carbohydrate

degradation by bacteria are therefore present in higher

concentrations in the stools and are held in contact with the

colonic mucosa for longer periods of time.

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2. High content of refined carbohydrates which contain

less of vitamins A, C, and E, which act as oxygen-radical

scavengers.

3. Excess intake of red meat: High cholesterol intake in red

meat enhances the synthesis of bile acids by the liver,

which in turn may be converted into potential carcinogens

by intestinal bacteria.

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* Morphology:

- The distribution of the cancers in the colorectum

is as follows:

• Rectosigmoid colon 55%.

• Cecum/ascending colon 22%

• Transverse colon 11%.

• Descending colon 6%.

• Other sites 6%.

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• Tumors in the proximal colon tend to grow as

polypoid, exophytic masses. Obstruction is

uncommon.

• While carcinomas in the distal colon tend to be

ulcerative forming malignant ulcer or tend to be

infiltrative forming annular, encircling lesions that

produce malignant constrictions of the bowel.

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Ulcerative colonic carcinoma

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Polypoid colonic carcinoma

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Infiltrative colonic carcinoma(annular stricture)

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* Microscopically; cancer colon is

adenocarcinoma consists of malignant acini

separated by fibrovascular connective tissue

stroma.

• The tumor infiltrates the wall down to the

serosa according to the tumor stage.

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Adenocarcinoma

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Colonic adenocarcinoma: malignant acini infiltrates the wall.

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* Clinical Features:• Colorectal cancers remain asymptomatic for years.

• Ceacal and right colonic cancers cause fatigue,

weakness, and iron-deficiency anemia. These

bulky lesions bleed readily and may be discovered

at an early stage.

• Left-sided cancers cause occult bleeding, changes

in bowel habit, or crampy left lower quadrant

discomfort.

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• All colorectal tumors spread by direct extension

into adjacent structures and by metastasis

through the lymphatics and blood vessels.

• In order of preference, the favored sites of

metastatic spread are the regional lymph

nodes, liver, lungs, and bones.

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TNM Staging of cancer colonTis Carcinoma in situ

T1 Tumor invades submucosa

T2 Extending into the muscularis propria

T3 Penetrating through the muscularis propria into subserosa

T4 Tumor directly invades other organs or structures

N0 No regional lymph node metastasis

N1 Metastasis in 1 to 3 lymph nodes

N2 Metastasis in 4 or more lymph nodes

M0 No distant metastasis

M1 Distant metastasis

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* Complications of cancer colon:

1. Intestinal obstruction.

2. Bleeding per rectum and anemia.

3. Intestinal perforations.

4. Fistula formation.

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THANKS

References:Robbins and Cotran’s: Pathologic Basis of Disease. Seventh edition.