one rare cancer of the pleural surface, typically associated with
exposure to asbestos. It has a breathtakingly rapid natural history
with a median survival of 6 to 8 months when untreated
and a significant economic and social impact. MPM is a disease
with limited therapeutic options and its management is
still controversial. Diagnosis is usually made by thoracoscopy,
which allows multiple biopsies with histological subtyping
and is indicated for staging purposes in surgical candidates 1.
Signet-ring cell MPM is an uncommon histological subtype of
mesothelioma that exhibit signet-ring features and that can be
misdiagnosed as signet-ring cell adenocarcinoma 2. Exclusion
of pleural metastasis of signet-ring cell adenocarcinoma is the
critical point for differential diagnosis.
Here we report a case of pleural effusion diagnosed as MPM
with neoplastic cells that exhibit prominent signet-ring-like
features, which was identified by pleural effusion cell block
immunohistochemistry (IHC) and also confirmed by IHC of
histological sections from pleural biopsy specimen.
Results. A 71-year-old Caucasian male was admitted to
our hospital with dyspnea, fatigue and weight loss. His past
medical history was unremarkable, and he has not recently
used drugs. He does not have family history of note and was
not on regular medication. There was a history of exposure
to asbestos during the occupation. After clinical examination,
computed tomography of the chest showed left sided
massive pleural effusion and likely pleural plaques. A thoracentesis
was performed and serohemorrhagic fluid was
determined. Exfoliative cytological examination of pleural effusion
showed reactive mesothelial cells and some clear cells
discretely showing intracytoplasmic vacuoles and eccentric
atypical nuclei reminiscent of ‘‘signet-ring’’ cells. In view of
signet-ring cells, diagnosis of likely metastatic adenocarcinoma
with background mesothelial cells was done. Screening
for a primary tumor of other parts of the body was negative.
Pleural effusion cell block IHC was CEA, TTF-1, CK20,
CDX2 negative and CK5/6, CK7, EMA (membranous), WT-
1 (nuclear), calretinin positive suggesting a MPM diagnosis.
Finally, also immunohistochemical analysis of pleural biopsy
confirmed the diagnosis of MPM. The patient was considered
operable for his good performance status. It was performed a
pleurectomy/decortication surgery with atypical lung resection
of the left upper lobe. Histopathological examination
of surgical specimen detected a biphasic mesothelioma with
signet-ring-like features.
Discussion. Mesotheliomas have been classified into four
major histologic subtypes: epithelioid, sarcomatoid, mixed epithelioid
and sarcomatoid (biphasic), and desmoplastic, the most
common of which is epithelioid 3. The signet-ring configuration
seen in adenocarcinomas has traditionally been associated with
round shapes and eccentric nuclei and with the accumulation
of large amounts of intracytoplasmic mucin 4. Signet-ring cell
carcinomas can arise in a wide variety of organs, including
lung, stomach, colon, breast, urinary bladder, pancreas, salivary
glands, prostate, as well in stromal tumors of the ovary and
testis 5-9.
Conclusions. This case illustrates that pathologists should know
that mesotheliomas can also present prominent signet-ring-like
features and that immunohistochemistry of histological sections
from a cell block combined with the immunohistochemical
studies may be helpful to determine the type of malignancy.
