Page 427 - Concise Pathology for Exam Preparation ( PDFDrive )

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412 SECTION II Diseases of Organ Systems

- Also seen in this syndrome is melanotic mucosal and cutaneous pigmenta-
tion and increased risk of several malignancies including cancer of colon,
pancreas, breast, lung, ovaries, uterus and testicles. It is caused by a germ-
line mutation in LKB1/STK11 gene that encodes a serine/threonine protein
kinases.
- Present as large and pedunculated polyps with a lobulated appearance
- Histologically characterized by extensive connective tissue and smooth
muscle arborization (intermixing) throughout the polyp; the glands being
lined by normal looking intestinal epithelium
(iii) Cowden syndrome
- Hamartomatous polyps in GIT associated with an increased risk of neo-
plasms of thyroid, breast, uterus and skin
- Caused by a germline mutation in PTEN (phosphatase and tensin homo-
logue) tumour suppressor gene
- PTEN encodes a phosphatase that acts as an inhibitor of signals from sev-
eral tyrosine kinase receptors and favours apoptosis through the BAD/
BCL2 pathways
(iv) Cronkhite–Canada syndrome
- Nonhereditary polyposis seen in individuals over 50 years who present
with diarrhoea, weight loss, abdominal pain and weakness
- Hamartomatous polyps are seen in stomach, small intestine and colorec-
tum.
- Polyps are histologically similar to juvenile polyps.
- Intervening nonpolypoidal mucosa also shows crypt dilatation, oedema
and inflammation in the lamina propria.
- Other manifestations include nail atrophy or splitting, hair loss and hypo-
and hyperpigmentation of the skin.
(c) Hyperplastic polyps
(i) Epithelial proliferations that are thought to result from delayed shedding of
surface epithelial cells lead to piling of goblet and absorptive cells.
(ii) Hyperplastic polyps do not have a malignant potential.
(iii) The crowding gives rise to a serrated surface (histological hallmark).
(iv) A sessile serrated adenoma, which is histologically similar but has malignant
potential, needs to be differentiated from a hyperplastic polyp.
(v) Classically less than 5 mm and seen in left colon.
(vi) May be single or multiple
2. Neoplastic polyps (adenomas of the small and large intestine)
(a) Are variable in size and may be pedunculated or sessile; show a progressive increase
in incidence with increasing age (peak incidence after 60 years)
(b) Familial predisposition present; males and females are equally affected
(c) All adenomas are a result of proliferative epithelial dysplasia and may give rise to
invasive carcinomas
(d) Adenomas are classified into four types based on epithelial architecture:
(i) Tubular adenomas
(ii) Villous adenomas
(iii) Tubulovillous adenomas
(iv) Sessile serrated adenomas
(e) Malignant transformation depends on polyp size, histological architecture and se-
verity of epithelial dysplasia. Villous adenomas greater than 4 cm in diameter are
likely to undergo malignant transformation.

Tubular adenomas
• May arise anywhere in the colon; about half are found in the rectosigmoid
• May be solitary or multiple
• Large adenomas usually have a slender stalk 1–2 cm long with a raspberry-like head

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