Case report:
A 36-year-old non-alcoholic female with a history of smoking for 15
years, presented with abdominal pain radiating to the back. The pain was
not relieved by NSAIDS.
The patient mentioned that she had experienced many episodes of
non-bilious vomiting, nausea and intermittent non-bloody diarrhea. On
physical examination, a mass was palpated in the epigastric region. Lab
tests were normal except for a mild anemia. The radiological findings on
Ultrasound (US) and non-contrast Computed tomography (CT) revealed
multiple cystic lesion in the tail of the pancreas attached to the
spleen. Fig.1
The patient underwent distal pancreatectomy with splenectomy and the
specimen was sent to the pathology department.
Grossly, the specimen was composed of the distal part of the pancreas
adherent to the spleen, where a cystic mass measuring about 8 cm in
diameter was found, the rest of pancreas tissue measured 4x6 cm. The
spleen measured 6×10 ×15 cm Fig. 2 . In addition, three regional
lymph nodes were detected. The pathologist’s first impression was a
pancreatic pseudocyst, but also other cystic neoplasms of pancreas could
not be excluded.
Microscopically, In the wall of the cyst there were nests of neoplastic
histiocyte ̵̵ like cells without significant cellular atypia Fig.
(3 ̵̵ 4).No evidence of vascular invasion was found. The lymph nodes,
the spleen and the surgical margins were tumor free.
Beside Hematoxylene and Eosin (H&E) stains, IHC was recommended to
figure out the diagnosis. The IHC revealed positivity of the tumor cells
for CD56 Fig.5 and Cyclin D1. In addition, NSE was weak
positive, whereas pan Cytokeratin (CK), CK7, CK20, Chromogranin A,
synaptophisin, CD68, S100, Vimentin, Epithelial membrane antigen (EMA),
and smooth muscle actin (SMA) were negative.
Based on H&E stain and IHC, the diagnosis was limited between SPT and
NET of pancreas. The morphologic features of the cells and the lack of
β-catenin stain lead to signing out this case as a well-differentiated
endocrine tumor (G1-NET) with almost total cystic degeneration. After a
year β-catenin and E-Cadherin stains were performed and the tumor cells
showed a positivity for β-catenin and negativity of E-CadherinFig. (6 ̵̵7). Therefore, the diagnosis of solid pseudopapillary
tumor of pancreas was the final diagnosis.
Discussion: Solid pseudopapillary tumors are rare
low-grade malignant neoplasms, commonly located in the tail of
pancreas[4]. Necrosis and cystic degeneration are common features
[5, 6]. The ultrasound and the CT reveals well-defined solid masses
with cystic components [7](2).
Clinically, SPTP are usually non-symptomatic and discovered as an
abdominal mass by accident or during physical examination [3].
Complete lab tests are usually normal. Surgery is the gold standard
treatment with curative results if the lesion is completely resected
[4].
In our case, microscopic examination of a pancreatic cystic lesion
revealed nests of round monomorphic cells surrounded by a scant
fibrovascular stroma in the cyst wall. The cytoplasm of the cells was
clear to granulated and the nuclei were uniform round to oval with
finely and evenly distributed chromatin. No mitotic figures were
identified. Depending on the morphologic findings, the final
differential diagnosis was SPTP and NET.
The IHC results were as following: Chromogranin A was negative, as many
other immune stains, and the only positive stains were CD56, NSE, and
cyclin D1. At that time, E-cadherin and β-catenin were not available in
our lab. Therefore, we favored the diagnosis of low-grade NET.
One year later, E-cadherin and β-catenin were available. Because the
tumor cells were negative for E-cadherin with nuclear positivity for
β-catenin, we redeemed our diagnosis from NET to SPTP.
SPTs can show significant morphological overlap with NETs but the
unclear invasion, clear cytoplasm and nuclear groove in tumor cells
support the diagnosis of SPT more than PanNETs [4] Although
morphological characteristics of the tumor cells and IHC stains play an
essential role in distinguishing between these two neoplasms, their rule
is not absolute and an overlap between the two tumor was also documented
immunohistochemically. Some studies, demonstrate that E-cadherin and
β-catenin are the most useful immunostaining markers to differentiate
between them[8]. Our case supports this fact.
Eighteen months following the surgery, Ultrasound revealed no recurrence
or metastases. Thus, proving the good prognosis of SPTP.
Conclusion: Solid pseudopapillary tumor should be
included in the differential diagnosis of every pancreatic cystic lesion
and both morphology and IHC lead to the definitive diagnosis. These
tumors and Neuroendocrine tumor (NET) of the pancreas should be
distinguished from each other. SPT-specific markers such as β-catenin
are recommended, even if the tumor has a NET-like morphology.