2018, Volume 34, Number 3, Page(s) 207-214
Gastrointestinal Stromal Tumors: A Clinicopathological and Immunohistochemical Study of 65 Cases
Merih TEPEOĞLU1, Gonca ÖZGÜN1, M. Zeyneb TUNCA1, Tugan TEZCANER2, B. Handan ÖZDEMIR1
1Department of Pathology,Başkent University Faculty of Medicine, ANKARA, TURKEY
2Department of General Surgery, Başkent University Faculty of Medicine, ANKARA, TURKEY
Keywords: Gastrointestinal stromal tumors, Necrosis, Ki-67, CD-34
The clinical behavior of gastrointestinal stromal tumors is divergent. The aim of the present study was to define the clinicopathological
features that determine the patients outcome.
Material and Method: Sixty-five gastrointestinal stromal tumors were reviewed with their histological, immunohistochemical and clinical
features and compared with their clinical outcome statistically.
Results: Tumors were located in the stomach (n=39, 60%), small intestine (n=22, 33.8%) and large intestine (n=4, 6.2%). Immunohistochemically,
CD 117 positivity was found in 90.8%, whereas CD34, Smooth muscle actin, Desmin and S100 positivity was found in 73.3%, 61.7%, 11.7% and
28.3% of tumors respectively. All six CD 117-negative cases expressed DOG-1. The mean Ki-67 proliferation index was 8.69%±12.76. Liver
metastasis was detected in seven cases. A significant association was detected between decreased mean survival time and increased tumor size
(p<0.001), large bowel localization (p=0.047), mitosis (p<0.001), the presence of necrosis (p=0.001), metastasis (p=0.033), Ki-67 proliferation
index (p=0.002) and risk category (p<0.001). CD 34 positivity was mostly seen in the stomach (p=0.001), and CD 34 positive tumors had longer
overall survival (92.85.±5.77 months versus 67.21±13.68 months) (p=0.046). Higher Ki-67 proliferation index (≥6%) was also correlated with
the presence of metastases (p=0.015).
Conclusion: Our study indicates that in addition to well-known risk factors such as increased tumor size, high mitotic activity and metastasis;
higher Ki-67 proliferation index, the presence of necrosis, and CD34 negativity also correlate with shorter survival time.
Gastrointestinal stromal tumors (GISTs) are the most
common mesenchymal tumors of the digestive tract. GISTs
can occur at every level of the gastrointestinal tract, but most
commonly in the stomach (60-70%), and small intestine
(20-30%). Rarely, they can be seen in extragastrointestinal
locations, like the omentum, retroperitoneum, and
. GISTs occur by neoplastic transformation
of the interstitial cell of Cajal, the mesenchymal derived
intestinal pacemaker cells 1-4
. These cells specifically
express the tyrosine kinase receptor c-kit (CD 117).
Although several GISTs show strong histomorphological
similarities, they have different immunophenotypes
and biological behavior, and this diversity yields various
confusing data in the literature 1-7
. The purpose of this
study was to determine the clinicopathologic features of 65
GISTs and reveal the pathological factors that negatively
influence overall survival.
A total of 65 cases that were diagnosed as GIST at Baskent
University, Department of Pathology between January 2003 and April 2016 and having survival data were included in
the study. The study protocol was approved by the local
Ethics Committee of the University Hospital. Each case was
reviewed for tumor localization, tumor size, predominant
cell type, mitotic activity/50 high power fields (HPF), the
presence of coagulative necrosis, and Ki-67 proliferation
rate. Mitoses were counted in the most cellular areas. All
cases were immunohistochemically stained with CD 117,
Smooth muscle actin (SMA), Desmin, S100, and CD 34.
Additionally DOG1 (discovered on GIST-1) was used in
CD 117 negative cases. The staining pattern of CD 117 was
considered as diffuse if the number of positive cells was
≥50% and focal if <50%. The staining intensity was evaluated
as mild or intense. Clinical data and follow-up information
was obtained from medical records. The risk stratification
of GISTs classification was evaluated according to the
Armed Forces Institute of Pathology (AFIP) classification
(Miettinen and Lasota criteria) Accordingly, tumors were
classified as very low-risk, low-risk, intermediate risk or
high-risk, based on tumor localization (stomach/jejunum
or ileum/duodenum/rectum), mitotic rate (≤5 /50 HPF or
>5/50 HPF) and tumor size (≤2 cm, >2-≤5 cm, >5-≤10 cm
and >10 cm) (2-5).
Statistical analysis of the data was done with SPSS for
Windows 13.0 statistical package software. Demographic
variables were detected by descriptive statistics. Standard
error of mean was presented in parametric values while
standard deviation was used in non-parametric values.
Categorical data were examined using the Chi-square test.
Pearsons Chi-square and Fishers exact tests were used to
assess the association between categorical variables. The
statistical comparison of the median values of groups was
done by the Mann-Whitney U and Kruskal-Wallis tests.
The KaplanMeier method was used to determine the
disease-free survival rate. Survival curves between two
categories were compared using a Log-rank test. A p value
<0.05 was required for statistical significance.
The patient group included 34 women (52.3%) and 31
men (47.7%) whose ages ranged from 24 to 93 years (mean, 61.75±15.77 years). The most common symptom
was abdominal pain (68.4%), followed by abdominal
mass (22.2%). Among 65 patients, 26 (40%) underwent
complete surgical resection and 39 (60%) underwent
segmental resection or excision. After surgery, 30 (46.1%)
patients had imatinib therapy. Thirty-nine (60%) tumors
were localized in the stomach, while 22 (33.8%) were in the
small and 4 (6.2%) were in the large intestine. The size of
tumor ranged between 0.5 cm and 37 cm, with a mean of
6.5±5.7 cm. The mean number of mitoses were 4.21± 7.06
(Minimum: 0-maximum: 50/50 HPF). Metastasis was seen
in 7 (8.6%) patients with the metastatic site being the liver
in each case. Clinicopathological parameters of all 65 cases
are shown in Table I
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|Table I: Clinicopathological characteristics with mean survival months of 65 cases with GISTs.
Morphologically, 44 cases (67.7%) had pure spindle cell
morphology, while 2 (3.1%) had pure epithelioid cell and 19
(29.2%) had mixed morphology. Immunohistochemically, CD117 positivity was detected in 59 (90.8%) of 65. The
staining pattern was diffuse in 43 patients (66.2%), while
it was focal in 16 patients (24.6%). Density of staining
was intense in 38 patients (58.5%) and mild in 21 patients
(32.3%). No statistical significance was found between the
CD 117 staining pattern or density with tumor localization
or the other clinicopathological parameters. All of the
six CD 117 negative cases showed DOG1 positivity and
4 of them were also positive for CD 34 and SMA. The
distribution of expression of immunohistochemical
findings according to localizations is shown in Table II.
A statistically significant association was found in CD 34
expression between stomach and non-stomach tumors. CD
34 positivity was mostly seen in stomach tumors (p=0.001);
however, there were no statistically significant associations
between CD 117, SMA, desmin and S100 expression and localization (p>0.05). The mean Ki-67 proliferation
index was 8.69±12.76% (Range: 1% to 65%). The cases
of intestinal and gastric GISTs with morphological and
immunohistochemical findings are shown in Figure 1A-E
and Figure 2A-E respectively.
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|Table II: The expression of immunohistochemical markers according to localizations.
Click Here to Zoom
|Figure 1: A) A case of intestinal stromal tumor, that is localized in submucosa (H&E; x40). B) Diffuse CD 117 positivity in this case (IHC;
x40). C) GIST with epithelioid morphology in the small intestine (H&E; x40). D) CD 117 is negative in this case. Note that the infiltrating
mast cells are positive with CD 117 (IHC; x100). E) Tumor cells show diffuse membranous and cytoplasmic positivity for DOG1 (IHC;
Click Here to Zoom
|Figure 2: A) A case of gastric GIST with spindle cell morphology is seen (H&E; x40). B) CD 34 positivity is seen in this case (IHC; x100).
C) A case of gastric GIST with epithelioid cell morphology is shown (H&E; x40). D) Tumor cells are negative for CD 34, whereas vascular
channels as internal control are positive for CD 34 (IHC; x100). E) Tumor cells show diffuse membranous and cytoplasmic positivity for
DOG1 (IHC; x100).
Statistically significant associations were also detected
between risk category and, the presence of necrosis
(p=0.001), Ki-67 proliferation index (p=0.002) and
the presence of metastasis (p=0.005). With increasing
risk category, the presence of necrosis and metastasis,
were found to increase. Ki-67 proliferation was also
found to be highest in the high-risk category (p=0.002).
However no statistically significant association was
observed between risk category and tumor cell type
(p=0.24), expression of CD 117 (p=0.89), SMA (p=0.49),
Desmin (p=0.82), CD 34 (p=0.09) and S 100 (p=0.90).
With increasing tumor size, the presence of metastasis was
also increased (p=0.011). Both high mitotic index values
(>5/50 HPF) and high Ki-67 proliferation index (≥6%)
were correlated with the presence of metastases (p=0.08,
The mean follow-up time for the 65 patients was 88.05±41.5
months (range 1 to 152 months). Throughout the followup
period, 15 of 65 patients (23.1%) died at a mean time of
57.83±42.1 months (range 1 to 121 months). Cause of death
in all of these patients was related to disease recurrence with
10 (66.7%) having a tumor located in the stomach, 3 (20%)
in the small intestine and 2 (13.3%) in the large intestine.
The remaining 50 patients (76.9%) were living without
recurrence for a mean period of 95.76.±38.1 months. The
relationship between the clinicopathological findings of 65
patients and their prognoses is given in Table I.
Univariate analysis demonstrated that large bowel
localization in the gastrointestinal site (p=0.047), tumor size
larger than 5 cm (p<0.001), mitotic count higher than 5/50
HPF (p<0.001), Ki-67 proliferation index equal to or higher
than 6% (p=0.002), the presence of necrosis (p=0.001), and
the presence of metastasis (p=0.033) indicated shorter
overall survival than their corresponding groups.
No significant correlation was seen between overall
survival and gender (p=0.739), and tumor cell type
(p=0.355), although patients whose tumors included an
epithelioid cell type had shorter mean survival time than
patients who did not (Table I). No significant correlation
was found between mean survival and CD 117, SMA,
Desmin and S100 immunoreactivity (p=0.909, 0.661, 0.791,
0.561 respectively). However, a significant association was
detected between CD 34 expression and survival (p=0.046),
in that patients with CD 34 positive tumors had longer
overall survival than those with CD 34 negative tumors
(survival time was 92.85±5.77 months in CD 34 positive
tumors versus 67.21±13.68 months in CD 34 negative
Kaplan-Meier analysis revealed that 3, 5 and 10-year
overall survival rates were respectively 90%, 80%, and 78%
in our patients. 10-year overall survival was 86% in patients
with <5 cm tumor size and 61% in those with ≥5 cm tumor
size (p=0.017). While 10-year overall survival in patients
who had ≤5 mitoses per 50 HPF was 80.8%, it was 69% in
those who had >5 mitoses/50 HPF (p=0.332). As for Ki-67
proliferation, 10-year overall survival was 84% for patients
rated <6% and 65% for those rated ≥6% (p=0.064). Kaplan-
Meier plots are given in Figure 3A-C.
Click Here to Zoom
|Figure 3: Kaplan-Meier plots of overall survival for GISTs
grouped according to mitosis (A), Ki-67 proliferation index (B)
and tumor size (C).
GISTs have a broad and divergent spectrum of biological
behavior ranging from a benign to a malignant disease
course. For many years, a variety of prognostic factors
have been searched to predict these tumors outcome.
Fletcher et al. published the first risk classification system
for GIST in 2002, which is currently named the National
Institutes of Health (NIH) classification. Based on size and
mitotic count in 50 high power fields (HPF), a four grade
scale (very low risk, low risk, intermediate risk and high
risk) to predict biological behavior was proposed 5
classification system was employed in several studies 7-9
In 2006, Miettinen and Lasota proposed a new classification
based on the evaluation of 1765 GISTs of the stomach and
906 GISTs of the small intestine, which is also known as the
Armed Forces Institute of Pathology (AFIP) classification
. In this classification system, the anatomic site of
the primary tumor was introduced as additional criteria
in risk assessment 2-4
. Several researchers evaluated
NIH consensus criteria and proposed a revision of the
AFIP criteria 9-11
. Thereafter, in 2010, the first TNM
classification of GIST was published, based on three major
prognostic factors; site, size, and mitotic rate 12
then, numerous studies have been published about both
the use of this risk category and additional prognostic
parameters, predicting the clinical course of these tumors.
Tumor size and mitotic rate have been regarded as the most
reliable parameters for determining prognosis by many
authors 7-16. DeMatteo et al. mentioned that tumor size
was a significant factor for an adverse outcome in their
report involving 200 GISTs 14. Similarly, Miettinnen et
al. have mentioned that tumors smaller than 2 cm have
lower risk of progression in all locations, and tumors
larger than 5 cm in the small intestine and greater than 10
cm at gastric sites were reported to be more aggressive in
behavior 3,7. However, they also emphasized that tumor
size could not predict the prognosis by itself after detecting
that tumors which were bigger than 10 cm concurrently
with low mitotic activity have relatively better prognosis
than same size tumors with high mitotic activity, in their
report involving 1765 gastric GISTs 3. Likewise, in 2008,
DeMatteo et al. emphasized that more than 5 mitoses per
50 HPF and tumor size greater than 10 cm were the two
significant independent factors that negatively influence
disease-free survival 15. Similar to the literature, larger
tumor size (≥ 5 cm) and higher mitotic index (>5/50 HPF)
were correlated with poor overall survival in our study.
As suggested by Miettinen, tumor localization is an
important prognostic predictor in addition to tumor size and mitotic rate in GISTs 3,15-19. Emory et al. reported
that survival rates were worst for patients with small
bowel GIST tumors and best for those with esophageal
ones 19. Miettinnen 3 and Güler et al. 13 found that
small intestine tumors had more aggressive behavior than
tumors located in the stomach. DeMatteo et al. found that
patients with large bowel GIST experienced a high rate of
recurrence and only 20% were free of recurrence 15. In
our study, similar to DeMatteo, large bowel location had
the worst prognosis of all gastrointestinal localizations.
The Ki-67 proliferation index also appears to be another
very important prognostic factor in GIST. In some
reports, Ki-67 was considered as a good indicator of the
risk of metastasis 9,19,20. However there is controversy
regarding the cut-off values for Ki-67 levels, methods of
determination and its prognostic utility above the mitotic
rate. Nilsson et al. identified maximum Ki-67 proliferative
index (≥ 5%) as one of two independent risk factors
together with tumor size and they even proposed a two-tier
risk scoring system based on both maximum tumor size
and Ki-67 score 8. Nilsson et al. suggested that the Ki-67
proliferative index determined in hot spots has a stronger
predictive value than the mitotic rate 8. Similarly, due to
the difficulty of evaluating the mitotic count for quality of
slides and differences in interpretation, other authors as
Suster and Panizo-Santos et al. also suggested that the Ki-
67 index was a stronger prognostic indicator and superior
to using the mitotic rate 20,21. However, there are also
studies of Rudolph et al. in which the mitotic index was
seen as better predictive factor of prognosis 22. Similarly,
Şahin et al. showed a direct association between higher
mitotic count and low overall survival, but not with the
Ki-67 proliferation index 23. In our study, a statistically
significant association was found between mean survival
and the Ki-67 proliferation index. The patients whose
Ki-67 proliferation index was higher than 6% had shorter
overall survival than patients whose proliferation index
was lower than 6%. We did not find any superiority of the
mitotic rate and Ki-67 indexes to each other. However, we
noted the significant relationship between both indexes in
terms of survival.
Other prognostic parameters in patients with GISTs that
are reported to influence overall survival negatively are
male sex 9,16, epithelioid cell component 16 and the
presence of necrosis 13,24-26. Some authors did not
find any relationship between either histological subtype
and gender with survival 17. In our study, we noted the
significant association between the presence of necrosis
and overall survival. Although tumors with epithelioid cell morphology were found to be related with a lower
mean survival ratio, this was not found to be statistically
significant. The gender of patients also did not have any
prognostic impact on survival in our study group.
The histopathological diagnosis of GIST requires
immunohistochemical confirmation of CD 117 expression,
with either a diffuse or membranous staining pattern. CD
117 protein reactivity is reported between 72-100% in
different series 3,16,25. CD 117 positivity was detected
in 90.8% of our cases. The other immunohistochemical
markers that are used for diagnosis and differential
diagnosis of GISTs are SMA, desmin, CD 34 and S100.
The frequency of SMA, desmin, CD 34 and S100 have
been reported as 27-74%, 3-53%, 56-82% and 1-28%
respectively in the literature 3,16,25-27, and our results
were similar. The frequency of CD 34 and SMA expression
in GISTs varied depending on the site of occurrence 3,7.
While most esophageal and rectal GISTs are positive for
CD 34, small intestinal tumors are often positive for SMA
2,3,7. In our study, a statistically significant association
was found for CD 34 expression between stomach and
non-stomach tumors but CD 34 positivity was detected
mostly in the stomach. However there were no statistically
significant associations for CD 117, SMA, desmin and
S100 expression between localizations. Fujimoto et al.
considered positive S100 protein immunoreactivity to be
significantly associated with a poor prognosis in GISTs
16. While Miettinen et al. reported that SMA and desmin
positivity were prognostically favorable factors 7. In our
study, CD 34 positivity was found to be related with higher
overall survival but no significant association was found
between overall survival and CD 117, SMA, desmin and
In conclusion, the prediction of the clinical outcome
of GISTs is often difficult. Therefore it is important to
determine the pathological parameters that have an impact
on prognosis. In this study, the Ki-67 proliferation index,
the presence of necrosis, and the presence of metastasis
were found to be related with poor prognosis in GISTs in
addition to well-known predictive factors such as increasing
tumor size and high mitotic activity.
CONFLICT of INTEREST
The authors declare no conflict of interest.
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