Invasive breast carcinoma - IARC

A
B
Fig. 2.140 Cystic adenomatoid mesothelioma. A The tumour emanates from the uterus. B The lesion shows numerous cysts and vesicles in the extrauterine compon
e n t . C Even in the more solid areas of the extrauterine tumour, small cysts dominated microscopically.
C
abdominal or retroperitoneal component.
It grows along the serosa as multiple
translucent, fluid-filled cysts. Occasionally,
the cysts are solitary or form a
free floating mass.
Histopathology
The tumour is made up of multiple cysts
lined by one to several layers of flattened
or cuboidal mesothelial cells embedded
in a delicate fibrovascular stroma {3087}.
The lesions typically do not have atypia
or significant mitotic activity; however,
the occasional presence of cytological
atypia may lead to a misdiagnosis of
malignancy. Hobnail-shaped cells, foci of
mesothelial hyperplasia and, less frequently,
squamous metaplasia may be
seen. Fibrous septa are usually prominent
and may occasionally produce foci
with the appearance of an adenomatoid
tumour. The stroma may show marked
inflammatory change that make it difficult
to recognize the nature of the lesion.
Differential diagnosis
The chief differential diagnostic consideration
is malignant mesothelioma.
Attention to the macroscopic appearance,
i.e. multiple cysts rather than solid
plaque-like necrotic masses and the
usual absence of cytological atypia are
s u fficient to avoid the error in most
cases. Cystic lymphangioma may mimic
a multicystic peritoneal mesothelioma,
but the cells lining the former do not
express keratin.
Histogenesis
The majority of investigators consider
this entity to be an unusual type of
mesothelial neoplasm that has a tendency
to recur locally and may rarely transform
into a conventional mesothelioma
and show aggressive behaviour
{1039,3087}. Some investigators, however,
consider the lesion to be a non-neoplastic
reactive mesothelial proliferation
{2456}. A case termed cystic adenomatoid
mesothelioma showed a transition
from a uterine adenomatoid tumour and
is illustrated above.
Prognosis and predictive factors
These tumours have an indolent course,
but approximately one-half of cases
recur at intervals ranging from 1-27 years
{1410,2456}. There are rare instances of
multiple recurrences and of transformation
into a conventional malignant
mesothelioma {1039,3087}. In the largest
series 8% of patients with adequate follow
up died of tumour {3087}.
Adenomatoid tumour
Definition
A benign tumour of the peritoneum originating
from mesothelium and forming
gland-like structures.
Synonym
Benign mesothelioma.
Epidemiology
Peritoneal origin of this neoplasm is very
rare {571}.
Macroscopy
Lesions are usually solitary, less than 2
cm in diameter and have a white-grey
appearance.
Fig. 2.141 Adenomatoid tumour. Note the small tubules with prominent vacuolization.
Histopathology
Histologically, multiple, small, slit-like or
ovoid spaces are lined by a single layer
of low cuboidal or flattened epithelial-like
cells. Although adenomatoid tumours
can be confused with carc i n o m a s ,
nuclear atypia is absent or minimal, and
mitotic figures are infrequent. Notably,
adenomatoid tumours have no significant
intracellular mucin, as might be
found in neoplasms of müllerian origin.
Clinically, they are asymptomatic, and
Peritoneal tumours 199