Open Journal of Pathology, 2012, 2, 162-165
Published Online October 2012 (http://www.SciRP.org/journal/ojpathology)
http://dx.doi.org/10.4236/ojpathology.2012.24031
1
Gastric Neuroendocrine Carcinoma in a Dog
Nadja Herbach1, Stefan Unterer2, Walter Hermanns1
1Institute of Veterinary Pathology, Centre for Clinical Veterinary Medicine, Ludwig Maximilians University Munich, Munich, Ger-
many; 2Clinic of Small Animal Medicine, Centre for Clinical Veterinary Medicine, Ludwig Maximilians University Munich, Munich,
Germany.
Received July 11th, 2012; revised August 24th, 2012; accepted September 3rd, 2012
ABSTRACT
A gastric biopsy specimen from a 14-year-old Yorkshire terrier was analysed using light microscopy, immunohisto-
chemistry and transmission electron microscopy. The biopsies were obtained from a 3 × 3 × 4 cm mass located at the
gastric cardia. Light microscopy revealed solid nests and sheets of tumour cells separated by abundant fibrovascular
stroma in all gastric layers. The tumour cells were monomorphic, with eosinophilic cytoplasm and demonstrated
palisading at the periphery. Nuclei were round to oval with densely packed chromatin and inconspicuous nucleoli. The
tumour cells immunohistochemically stained strongly positive for chromogranin A, synaptophysin, and pan-cytokeratin.
Electron microscopy revealed electron dense neurosecretory granules of 100 - 150 nm in diameter. Metastases were
found in regional lymph nodes. Gastric neuroendocrine carcinoma was diagnosed, according to the histological, immu-
nohistochemical and electron m icroscopic featur es.
Keywords: Gastric Carcinoid, Gastric Neuroendocrine Carcinoma; Dog; Stomach
1. Introduction
Neuroendocrine (NE) cells may form glands (adrenal
medulla, parathyroid, paraganglia, adenohypophysis) or
may be diffusely distributed throughout the body in dif-
ferent organs, i.e. the gastrointestinal tract, p ancreas, skin,
thymus, thyroid, lung, bilary and urinary tract. These
diffusely distributed NE cells belong to the dissemi-
nated/diffuse neuroendocrine system, DNES [1]. The
DNES produces and secretes peptides and amines that
are essential for regulation of carbohydrate, protein and
fat metabolism [2]. NE cells can be identified, using im-
munohistochemistry for synaptophysin, chromogranin A,
neural cell adhesion molecule (NCAM, CD56) and neu-
ron specific enolase (NSE) [1].
Tumours arising from the DNES, i.e. neuroendocrine
tumours (NET) were formerly called argentaffinoma, en-
terochromaffin cell tumour, carcinoid or apudoma. NET
of the gastrointestinal tract of domestic animals are rare,
with few case reports of carcinoids occurring in the in-
testine of adult dogs, cats, cows and a horse [3]. Neuro-
endocrine neoplasms (NEN) of the pancreas and gastro-
intestinal tract in man are considered potentially malign-
nant and are classified as well differentiated NEN (NET
with low grade malignant behaviour G1 (carcinoid) or
uncertain behaviour G2), or as poorly differentiated NEN
or neuroendocrine carcinoma (NEC) with highgrade ma-
lignant behaviour (G3), exhibiting a high proliferation
rate. NEC can be further subdivided into a small-cell and
a large-cell variant [1,4]. In animals, intestinal carcinoids
are also considered malignant, grow locally invasive,
infiltrating the submucosa and muscularis, and metasta-
size widely [3].
In humans, gastric NETs are the most frequent NETs
and can be divided into four subtypes. Type 1 is the most
frequent gastric NET, arising secondary to autoimmune
chronic atrophic corpus gastritis where loss of gastric
parietal cells leads to insufficient production of intrinsic
factor and hypochloric acid. Achlorhydria stimulates
gastrin-producing G-cells, causing hypergastrinaemia,
which in turn stimulates proliferation of enterochromaf-
fin-like (ECL) cells, and ultimately leads to the formation
of multiple, usually small tu mours [1]. Th e other types of
gastric NETs are rare and include type 2 NETs that occur
in association with multiple en docrine neoplasia (MEN1)
and Zollinger-Ellison syndrome. Type 3 are sporadic
NETs that are solitary, and Type 4 NETs are undifferen-
tiated gastric carcinomas that are usually large and have
metastasized at the time of diagnosis [1,5]. In animals, no
association between gastrinoma and gastric NET can be
made due to scarcity of both forms of NETs [2].
2. Methods
Biopsy samples of a 14-year-old Yorkshire terrier were
submitted to histological examination. The dog showed

Gastric Neuroendocrine Carcinoma in a Dog 163
chronic vomiting and a gastric mass was evident in ab-
dominal sonography. During endoscopy and laparoscopy
at the Small Animal Clinic, LMU Munich, a biopsy of a
3 × 3 × 4 cm mass located at the gastric cardia, and bi-
opsy samples of liver, pancreas and lymph nodes were
obtained and fixed in 10% phosphate-buffered formalin.
Biopsy samples were embedded in paraffin wax and rou-
tinely processed for light microscopy. Immunohisto-
chemistry was performed on paraffin wax sections. An-
tigen retrieval was performed using proteinase K (synap-
tophysin, cytokeratin) or microwave pre-treatment with
citrate buffer (pH 6.0) for 20 minutes (chromogranin A,
Vimentin, S100). Primary antibodies used for immuno-
histochemistry included rabbit anti chromogranin A
(1:500 in PBS pH 7.4, Dako Deutschland GmbH, Ham-
burg, Germany), rabbit anti neuron-specific enolase
(1:500 in PBS, Biomol GmbH, Hamburg, Germany),
rabbit anti synaptophysin (1:100 in PBS, Dako), mouse
anti vimentin (1:300 in PBS, Dako), rabbit anti S100
(1:400 in PBS, Dako), and mouse anti cytokeratin (1:50
in PBS, Dako). A biotinylated secondary antibody was
used to detect antibodies against chromogranin A, neu-
ron-specific enolase, S100 and synaptophysin, using the
avidin-biotin complex method (VECTOR Laboratories
Ltd., Peterborough, United Kingdom), and a peroxidase
conjugated antibody was used to detect antibodies against
cytokeratin and vimentin (Dako); DAB served as chro-
mogen. Samples of 1 mm3 were taken from paraffin
blocks for transmission electron microscopy, dewaxed,
contrasted in osmium tetroxide and embedded in Epon
resin.
3. Results
Grossly, the gastric biopsy sample was irregularly shaped
with a tan to brown cross-section. Histologically, the
sample consisted of nests and cords of monomorphic
round to oval cells, sometimes showing peripheral pali-
sading. The tumour cells had eroded the mucosa and
deeply invaded the submucosa and muscularis. Their
cytoplasm was slightly granular and nuclei were round to
oval. The mitotic index was low (2 - 10 per 2 mm2), and
atypia were uncommon. The tumour cell nests and cords
were separated by an abundant fibrovascular stroma with
lymphocytic infiltrates sometimes forming follicles (Fig-
ures 1(a) and (b)). Vascular invasion into venous blood
vessels was observed in some locations (Figure 1(c)).
The lymph node biopsy contained numerous similar tu-
mour cells, whereas the liver and pancreas samples
showed no evidence of metastases (not shown).
Immunohistochemically, tumour cells of the stomach
were positive for chromogranin A, synaptophysin, and
cytokeratin. Few tumour cells were positive for S100
(sustentacular cells) and the tumour was negative for
neuron-specific enolase and vimentin (Figures 2(a)-(f)),
(a)(b)
(c)(d)
Figure 1. Histology of the gastric tumour. (a) Uniform tu-
mour cells are arranged in nests and cords, separated by
abundant fibrovascular stroma, multifocal mononuclear
infiltrates may be seen in the surrounding connective tissue,
H & E stain, bar 200 μm; (b) Tumour cells arranged in
nests with peripheral palisading, bar 50 μm; (c) Vascular
invasion, anti-cytokeratin immunohistochemistry, bar 50
μm; (d) Transmission electron microscopy showing electron
dense secretory granules, bar 500 nm.
(a)(b)
(c)(d)
(e)(f)
Figure 2. Immunohistochemistry of the gastric tumour.
Immunohistochemical staining for (a) Cytokeratin; (b) Syn-
aptophysin; (c) Chromogranin; (d) S100 protein; (e) Neu-
ron-specific enolase; (f) Vimentin, bar 100 μm.
whereas the fibrovascular stroma was positive for
vimentin. Electron microscopically, tumour cells exhib-
ited few dense core secretory granules of 100 - 150 nm
diameter, with a large halo and a well designated limiting
membrane (Figure 1(d)). An intermediate grade gastric
neuroendocrine carcinoma was diagnosed based on the
location as well as histological, immunohistochemical
and electron microscopic features of the tumour cells.

Gastric Neuroendocrine Carcinoma in a Dog
164
The dog was euthanized two months after the diagnosis
was made due to deterioration of the general condition
and the poor prognosis. Unfortunately the body was not
submitted to post mortem examination.
4. Discussion
Gastric tumours are rare in domestic animals and gastric
NETs have only been reported in dogs to date [2]. Ac-
cording to the Veterinary WHO classification of tumours
of the alimentary tract, NET of the stomach (also called
carcinoid or neuroendocrine carcinoma, NEC) are de-
fined as low-grade malignant tumours with neurosecre-
tory granules that are identifiable light microscopically,
immunohistochemically using special stains, or by elec-
tron microscopy [2,6,7].
Well differentiated NETs cannot simply be classified
by conventional histopathology with respect to their
growth pattern and cellular features [1]. According to the
human WHO classification, a gastric NEN larger than 2
cm, invading the T. muscularis is considered a well dif-
ferentiated low-grade NEC. Tumours up to 2 cm, con-
fined to the mucosa-submucosa with or without angioin-
vasion are classified as benign or low-grade NET and
poorly differentiated NEC are high-grade malignant [8].
There are few case reports on gastric NETs in dogs. A
gastric carcinoid was reported in a 13-year-old female
whippet that was presented with a 10-day history of
weakness and ataxia as well as was vomiting for 3 days.
Post mortem examination showed a 3.5 cm-diameter
erosive transmural lesion on the antral mucosa of the
stomach. Histologically, the tumour was described as a
poorly differentiated NEC with high mitotic rate, multi-
focal necrosis and invasion of blood and lymphatic ves-
sels. Metastases were observed in liver, spleen, kidney,
lungs, lymph nodes and brain [9,10]. More recently, gas-
tric carcinoids were reported in the Norwegian Lunde-
hund, a breed often afflicted by chronic atrophic gastritis
(CAG) and gastric tumours, including gastric carcinoma
and NEC [11,12]. The Lundehund is thought to develop
hyperplasia of gastric endocrine cells in response to de-
creased acid secretion and hypergastrinaemia, related to
CAG [11]. Four of eight gastric tumour-bearing Lunde-
hund exhibited gastric carcinoids, with metastases into
regional lymph nodes. Three animals showed liver me-
tastases, and in one dog, lung metastases were demon-
strated. An association of chronic atrophic gastritis and
gastric tumours is also described in humans that develop
type 1 gastric NET as a result of increased gastrin pro-
duction [1] .
Male dogs seem predisposed to developing gastric tu-
mours, and the dog in the present study as well as three
of four affected Norwegian Lundehund were reported to
be male [6,11]. In humans, male predominance is re-
ported for sporadic (type 3) NET and undifferentiated
gastric carcinoma (type 4 NET) [1].
Immunohistochemically, NET cells stain positive for
chromogranin, synaptophysin, NCAM/CD56 and may be
positive for a variety of peptide hormones (e.g. ACTH,
calcitonin) and biogenic amines (e.g. serotonin) [1,3,13].
Likewise, the tumour in the present study was positive
for chromogranin A, synaptophysin and cytokeratin, and
the tumour of the female whippet, in contrast to the pre-
sent case, was additionally positive for NSE [9]. In the
Lundehund, gastric NET was confirmed by chromo-
granin A and synaptophysin immunohistochemistry [11].
Metastases were found in all reported cases. In the pre-
sent study only the biopsy specimen of the lymph node
showed metastases, however, due to the small size of
pancreatic and liver biopsies that were taken during
laparoscopy, we can not exclude distant metastases that
may have been overlooked. The invasive growth and
invasion of blood vessels however makes distant metas-
tases likely and argues for malignant behaviour. The mi-
totic index of the gastric NET identified in the present
report was fairly low (2 - 20 per 2 mm2), which is com-
parable to the mitotic index of gastric NET in the Lun-
dehund but sligh tly lower than that of the female whip pet
[9,11]. According to the human and veterinary diagnostic
criteria, the present case of a gastric NET would be des-
ignated as a well-differentiated intermediate-grade (G2)
maligna nt NET/NEC.
5. Acknowledgements
We thank Elisabeth Kemper and Karin Stingl for excel-
lent technical assistance
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