CHAPTER 3 Tumours of the Stomach - Pathology Outlines

A
B
C
Fig. 3.42 A, B, C Low-grade B-cell MALT lymphoma. A, B Lymphoepithelial lesions. C Immunostaining for cytokeratin highlights lymphoepithelial lesions. D Diffuse
large B-cell lymphoma; the neoplastic cells focally infiltrate glandular epithelium to form structures reminiscent of lymphoepithelial lesions.
D
eradication are characteristic. The lamina
propria appears ‘empty’ with gland
loss. Scattered lymphocytes and plasma
cells are seen within the lamina propria
and there are usually focal nodular collections
of small lymphocytes. These collections
frequently contain a mixture of
B- and T-cells and may be based on follicular
dendritic cell networks.
In most cases, the appearances are
insufficient for a diagnosis of residual
lymphoma. The significance of these
lymphoid nodules remains uncertain. In
cases showing partial regression or no
change following H. pylori eradication,
the lamina propria contains an infiltrate
morphologically indistinguishable from
that seen at diagnosis, but in these treated
cases lymphoepithelial lesions may
be very scanty or absent. In some cases
of partial regression and in cases with
relapsed low-grade MALT lymphoma following
H. pylori eradication, the lymphoma
may be largely confined to the submucosa
with only minimal involvement of
the mucosa.
PCR based diagnosis
The role of genetic analyses in the diagnosis
and follow up of low-grade MALT
lymphoma remains controversial. Up to
10% of well characterized cases of MALT
lymphoma identified as clonal through
demonstration of rearrangement of the
immunoglobulin heavy chain gene by
Southern blot fail to show a clonal pattern
when examined for immunoglobulin
heavy chain gene rearrangement by PCR
using fresh frozen tissue {418}. This false
negative rate increases if paraffin embedded
material is studied {417}. Several
studies have revealed by PCR the presence
of clonal B-cell populations in biopsies
from patients with uncomplicated
chronic gastritis and no morphological
evidence of lymphoma {1677, 225, 388}.
In conjunction with histological assessment,
PCR studies may be useful in monitoring
regression of MALT lymphomas
following conservative therapy {25}.
However, PCR detected clonal B-cell
populations may still be detected in
cases showing complete histological
regression. Some, but no all of these will
eventually show molecular regression but
there may be a prolonged time lag
between histological and molecular
regression {1677}. In the absence of histological
evidence of residual lymphoma,
the clinical significance of a persistent
clonal population remains uncertain.
Progression to high-grade lymphoma
The emergence of clusters of large transformed
‘blastic’ B-cells reflects transformation
to high-grade lymphoma {383}.
Eventually, these areas become confluent
to form sheets of cells indistinguishable
from the cells of a diffuse large
B-cell lymphoma. As long as a low-grade
component remains, these tumours may
be termed high-grade MALT lymphomas
but during further progression, all traces
of the pre-existing low-grade lymphoma
are lost, making it impossible to distinguish
the lesion from a diffuse large
B-cell lymphoma of unspecified type. In
cases with both low- and high-grade
components, genetic studies have con-
60 Tumours of the stomach