14
Alimentary Tract (Esophagus, Stomach, Small Intestine, colon, Rectum, Anus, Biliary Tract)
Fig. 14.21 Gastrointestinal stromal tumor. (A, B) This aspiration of a GIST is composed of loose clusters of atypical spindled and cells. (C) Fragments of cell
block material from EUS-guided FNA contain interlacing fascicles of atypical spindled cells. (D) The tumor cells are stained strongly positive for C-Kit (CD117)
(Papanicolaou H&E and x HP).
Several problems exist with the cytologic diagnosis of gastric
stromal neoplasms in brushings. First, the tumor cells may not
even be present in the smears. The overlying mucosa must be
ulcerated for the tumor to be sampled. Even when neoplastic
elements are present, they may be difficult to distinguish from
reactive cells, e.g. the fibroblasts of granulation tissue associated
with a peptic ulcer. Most authors claim that the diagnostic sen-
sitivity of brushings for gastric stromal neoplasms is quite low.
Even when neoplastic cells can be recognized, their histogen-
esis may not be readily identified. Furthermore, the question of
benign versus malignant may be impossible to answer; however,
this is not unique to brushings but also exists for small endo-
scopic biopsies. The overall diagnostic yield may be improved
with a more widespread use of endoscopic fine-needle aspi-
rates.26
Fortunately, we almost never rely on brushings to render this
interpretation. With its excellent ability to access mural masses,
EUS-guided FNA is currently the most effective approach for
sampling GISTs.154-159 It is not uncommon to recover abundant
material sometimes with numerous viable tissue particles iden-
tified. Paraffin-embedded cell block material is extremely useful
for immunohistochemical analysis particularly with regard to
C-Kit and CD34. Analysis of the C-Kit gene by polymerase chain
reaction (PCR) can also be used to confirm the diagnosis of
GIST.157,159 Confirmation of C-Kit leads to therapy with Gleevac
to which many of these tumors respond. Distinction between
benign and malignant GIST is best reserved for histologic exami-
nation and extensive sampling of the resected specimen.
The differential diagnosis of GIST includes leiomyoma and
leiomyosarcoma. Leiomyomas usually involve the esophagus
and submucosa of the colorectum and yield scant material on
aspiration biopsy. Leiomyosarcomas tend to show more signifi-
cant nuclear pleomorphism with more frequent mitotic figures
and a less prominent vascular pattern than GISTs. Ultimately
a definitive diagnosis of GIST rests on immunohistochemical
reactivity for C-Kit (Table 14.6).
carcinoid tumor (endocrine tumors)
Neuroendocrine neoplasms occur with some frequency through-
out the entire GI tract, most often in the appendix. The majority
of these represent conventional carcinoid tumors. In the stom-
ach, many arise in a background of well-developed atrophic
gastritis with endocrine cell hyperplasia as an intermediate
morphologic step.
Almost all patients with gastric carcinoid tumors are adults
who may present with upper abdominal pain, GI bleeding, or
the carcinoid syndrome. Rarely, other manifestations of endo-
crine overactivity may predominate. The most characteristic
endoscopic and gross appearance is that of a small submucosal
393
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