CHAPTER 3 Tumours of the Stomach - Pathology Outlines

Polyps
Hyperplastic polyps
Hyperplastic polyps are one of the commonest
gastric polyps. They are sessile
or pedunculated lesions, usually < 2.0
cm in diameter, typically arising in the
antrum on a background of H. pylori gastritis.
They contain a proliferation of surface
foveolar cells lining elongated, distorted
pits extending deep into the
stroma. They may contain pyloric glands,
chief cells and parietal cells. The surface
often erodes. In a minority of cases, carcinoma
develops within the polyps in
areas of intestinal metaplasia and dysplasia.
A
B
Fig. 3.23 A, B Examples of low-grade intraepithelial neoplasia of flat gastric mucosa. The atypia extends to
the surface.
ing; there is no stromal invasion. Mucin
secretion is absent or minimal. The pleomorphic,
hyperchromatic, usually pseudostratified
nuclei often are cigar-shaped.
Prominent amphophilic nucleoli are common.
Increased proliferative activity is
present throughout the epithelium.
Progression of intraepithelial neoplasia to
carcinoma
Carcinoma is diagnosed when the tumour
invades into the lamina propria (intramucosal
carcinoma) or through the muscularis
mucosae. Some gastric biopsies
contain areas suggestive of true invasion
(such as isolated cells, gland-like structures,
or papillary projections). The term
‘suspicious for invasion’ is appropriate
when the histological criteria for an invasive
malignancy are equivocal.
Up to 80% of intraepithelial neoplasias
may progress to invasion. Indeed, invasive
cancer already may be present in
patients found to have high-grade intraepithelial
neoplasia with no obvious
tumour mass. The extent of intestinal
metaplasia associated with intraepithelial
neoplasia, together with a sulphomucinsecreting
phenotype of the intestinalized
mucosa (type III intestinal metaplasia),
correlate with an increased risk of carcinoma
development.
Adenomas
Adenomas are circumscribed, benign
lesions, composed of tubular and/or villous
structures showing intraepithelial
neoplasia. The frequency of malignant
transformation depends on size and histological
grade. It occurs in approximately
2% of lesions measuring < 2 cm and in
40-50% of lesions > 2 cm. Flat adenomas
may have a greater tendency to progress
to carcinoma.
Fundic gland polyps
Fundic gland polyps are the commonest
gastric polyp seen in Western populations.
They occur sporadically, without a
relationship to H. pylori gastritis. They
also affect patients on long-term proton
pump inhibitors or patients with familial
adenomatous polyposis (FAP), who may
have hundreds of fundic gland polyps
{2064, 2065}.
The lesions consist of a localized hyperplasia
of the deep epithelial compartment
of the oxyntic mucosa, particularly
of mucous neck cells, with variable
degrees of cystic dilatation. Sporadic
fundic gland polyps have no malignant
potential. Exceptionally, patients with
attentuated FAP may develop dysplasia
and carcinoma in their fundic gland
polyps {2214, 1204}
Polyposis syndromes
Peutz-Jeghers polyps, juvenile polyps,
and Cowden polyps generally do not
occur spontaneously, but rather as part
of hereditary polyposis syndromes. In the
stomach, Peutz-Jeghers polyps are characterized
histologically by branching
bands of smooth muscle derived from
A B C
Fig. 3.24 High-grade intraepithelial neoplasia in flat gastric mucosa (flat adenoma). A Architectal distortion of the gastric glands. B High degree of cellular atypia.
C Papillary pattern.
48 Tumours of the stomach