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Pancreatic Gastrointestinal Stromal Tumor: Clinicopathologic Features and Prognosis

Liu, Zhen MM*; Tian, Yangzi MD; Xu, Guanghui MM*; Liu, Shushang MM*; Guo, Man BMed*; Lian, Xiao MStat*; Fan, Daiming PhD*; Zhang, Hongwei PhD*; Feng, Fan PhD*

Journal of Clinical Gastroenterology: October 2017 - Volume 51 - Issue 9 - p 850–856
doi: 10.1097/MCG.0000000000000719
LIVER, PANCREAS AND BILIARY TRACT: Original Articles

Goals: The present study aimed to investigate the clinicopathologic features and prognosis of pancreatic gastrointestinal stromal tumor (GIST).

Background: Reports on clinicopathologic features and prognosis of pancreatic GIST are limited due to the extremely rare incidence.

Study: One case of pancreatic GIST from our center and 44 cases reported in MEDLINE were enrolled in this study. Clinicopathologic features and prognosis of pancreatic GISTs were analyzed and compared with 297 gastric GISTs from our center.

Results: The most common location was head of pancreas (38.5%). The majority of pancreatic GISTs exceeded 5 cm (74.4%), displayed cystic or mixed imaging features (56.4%), and were high risk (85.7%). The 5-year disease-free survival (DFS) and disease-specific survival rates were 66.1% and 95.8%, respectively. Mitotic index was the only risk factor for DFS of pancreatic GISTs. The distribution of tumor size, histologic type and National Institutes of Health risk category were significantly different between pancreatic and gastric GISTs. The 5-year DFS rate of pancreatic GISTs was significantly lower than that of gastric GISTs. Multivariate analysis showed that location was an independent prognostic factor for DFS between pancreatic and gastric GISTs.

Conclusions: The most common location was head of pancreas. The majority of pancreatic GISTs were large and highly malignant. Pancreatic GISTs differed significantly from gastric GISTs in respect to clinicopathologic features. The DFS of pancreatic GISTs was worse than that of gastric GISTs.

*Division of Digestive Surgery, Xijing Hospital of Digestive Diseases

Department of Dermatology, Xijing Hospital, Fourth Military Medical University, Xi’an, Shaanxi, China

Z.L., Y.T., and G.X. contributed equally to this work.

This study was supported in part by grants from the National Natural Scientific Foundation of China (No. 31100643, 31570907, 81572306, 81502403, XJZT12Z03).

The authors declare that they have nothing to disclose.

Address correspondence to: Fan Feng, PhD, and Hongwei Zhang, PhD, Division of Digestive Surgery, Xijing Hospital of Digestive Diseases, Fourth Military Medical University, 127 West Changle Road, Xi’an 710032, Shaanxi, China (e-mails: surgeonfengfan@163.com; zhanghwfmmu@126.com).

This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal. http://creativecommons.org/licenses/by-nc-nd/4.0/

Received July 1, 2016

Accepted August 24, 2016

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal neoplasm of the alimentary tract and represents 1% to 2% of all gastrointestinal malignant tumors.1 GIST is considered to arise from the interstitial cells of Cajal (ICC), the pacemaker cells of the alimentary tract.2 In 1998, Hirota et al reported that GIST is associated with gain of function mutations in the KIT proto-oncogene.3 It has been established by immunohistochemical staining of GIST for CD117 and CD34.4 Histologically, most GISTs display spindle cell morphology (70%), whereas a minority is of epithelioid (20%) or mixed phenotypes (10%).5

GISTs occur anywhere along the gastrointestinal tract; they are most common in the stomach (50% to 60%) and the small intestine (30% to 35%) and less frequent in the colon and rectum (5%). GISTs that arise outside the gastrointestinal tract as primary tumor are designated as extragastrointestinal stromal tumors (EGISTs). The EGISTs are located in the mesentery, omentum, retroperitoneum, and pancreas, etc.6 Reports of pancreatic GIST are limited to individual case reports and case series of small numbers. Therefore, the present study was designed to evaluate the clinicopathologic features and prognosis of pancreatic GIST.

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MATERIALS AND METHODS

Cases of pancreas GIST were from our center and in addition from the literature. From May 2010 to March 2015, only 1 case of pancreatic GIST was diagnosed and received treatment in our center. Literature search of MEDLINNE was performed for all articles in English published from 2001 through 2015. MEDLINNE search resulted in 38 case reports7–44 including 44 patients. Finally, a total of 45 pancreatic GIST patients were identified. In addition, the clinicopathologic features and prognosis of pancreatic GISTs were compared with 297 gastric GISTs from our center. This study was approved by the Ethics Committee of Xijing Hospital, and written informed consent was obtained from the patient in our center.

Clinicopathologic data including age, sex, accompanied tumor, symptoms, location, tumor size, imaging features, surgical intervention, histologic type, lymph node metastasis, mitotic index, immunohistochemical features, mutational status, National Institutes of Health (NIH) risk classification, adjuvant imatinib therapy, and survival data were recorded. The tumors were classified into very low, low, intermediate, and high risk groups according to the modified NIH risk classification criteria reported by Joensuu.45 For survival analysis, the exclusion criteria were listed as follows: (1) with other malignant tumors, (2) with distant metastasis, (3) with GISTs in other locations, (4) with neoadjuvant imatinib therapy, (5) with tumor rupture during operation, (6) not receive R0 resection, (7) without follow-up data. Because of data acquisition, completeness of data are limited.

Data were processed using SPSS 16.0 for Windows (SPSS Inc., Chicago, IL). Numerical variables were expressed as the mean±SD unless otherwise stated. Discrete variables were analyzed using the χ2 test or the Fisher exact test. Risk factors for survival were identified by univariate analysis and Cox proportional hazards regression model was used for multivariate analysis. Evaluation for disease-free survival (DFS) and disease-specific survival (DSS) were obtained by the Kaplan-Meier method and differences between curves were compared using log-rank test. The P-values were considered to be statistically significant at the 5% level.

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RESULTS

The clinicopathologic features were summarized in Table 1. A total of 45 cases of pancreatic GISTs were collected in our present study. The patient age ranged from 30 to 84 years (median, 55 y; mean, 56.5 y). The most common location was head of pancreas (15/39, 38.5%). The tumors ranged from 1.8 to 35 cm in maximum diameter (median, 9.0 cm; mean, 11.0 cm). The mitotic index of 17 patients exceeded 5 of 50 high power field (17/40, 42.5%). Seventeen tumors displayed solid mass (17/39, 43.6%), 14 tumors displayed cystic mass (14/39, 35.9%) and 8 tumors showed mixed mass (8/39, 20.5%). Twenty-six patients displayed spindle cell morphology (26/38, 68.4%), 3 patients displayed epithelioid morphology (3/38, 7.9%) and 9 patients displayed mixed morphology (9/38, 23.7%). Nine patients were analyzed for gene mutation status. Two patients carrying a mutation in exon 9 of KIT, 4 patients carrying a mutation in exon 11 of KIT, 1 patient carrying a mutation in exon 18 of PDGFRA, 1 patient carrying a DNA polymorphism in exon 18 of KIT, 1 patient was wild type. Thirty-six patients (36/42, 85.7%) were classified as high risk according to NIH risk classification.

The relationship between imaging features and clinicopathologic characteristics were analyzed and summarized in Table 2. The imaging features were correlated with tumor size and histologic type. The majority of tumors with diameter >5 cm displayed cystic or mixed features (P=0.039). The majority of solid tumors displayed spindle cell morphology, however, only half of the tumors with cystic or mixed features displayed spindle cell morphology (P=0.016). Although there was no significant difference between imaging features and NIH risk category, all the tumors with cystic or mixed features were classified as high risk category (P=0.056).

Survival data of 29 patients were eventually selected for analysis using exclusion criteria described in the materials and methods (Table 3). The follow-up time ranged from 1 to 92 months (mean, 27.8 mo; median, 24 mo). Seven patients showed recurrence or metastasis, 1 patient suffered from GISTs related deaths. The 5-year DFS and DSS rates were 66.1% and 95.8%, respectively. The DFS and DSS of pancreatic GISTs were analyzed using the Kaplan-Meier survival analyses and shown in Figure 1.

Prognostic factors for DFS of pancreatic GISTs according to univariate analysis were summarized in Table 4. The results showed that only mitotic index was associated with prognosis of pancreatic GISTs. The DFS of pancreatic GISTs according to mitotic index was shown in Figure 2.

The clinicopathologic features of 45 pancreatic GISTs including age, sex, tumor size, histologic type, mitotic index, and NIH risk category were compared with 297 gastric GISTs from our center (Table 5). The results showed that the distribution of histologic type, tumor size, and NIH risk classification were significantly different between pancreatic and gastric GISTs (all P<0.001).

To explore the prognosis of GISTs, survivals of 29 pancreatic GIST patients and 217 gastric GIST patients with follow-up data were analyzed. As showed in Figure 3, the 5-year DFS rate of pancreatic GISTs was significantly lower than that of gastric GISTs (66.1% vs. 93.5%, P<0.001), while the 5-year DSS rate was comparable between the 2 groups (95.8% vs. 89.9%, P=0.653). The multivariate analysis showed that location (pancreas vs. stomach) was an independent prognostic factor for DFS (P<0.001) between pancreatic and gastric GISTs, but not for DSS (Table 6).

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DISCUSSION

This study represented the largest cases of pancreatic GIST so far. The clinicopathologic features and prognosis of pancreatic GISTs were analyzed and further compared with gastric GISTs from our center. We found pancreatic GISTs were larger in size and more malignant than gastric GISTs.

The most common location of the pancreatic GISTs was the head of pancreas, followed by the tail of pancreas. The location spectrum was similar to the largest series reported by Akbulut et al.42 It is well known that GISTs are considered to arise from ICC, the pacemaker cells of the alimentary tract. Yamaura et al39 have shown the presence of c-KIT positive interstitial cells surrounding the intercalated ducts and acinus in the pancreas. Popescu et al46 reported the existence of ICCs in the human exocrine pancreas which have a phenotype similar to the enteric ICCs. Wang et al47 have demonstrated that the c-Kit positive ICCs were mainly around the main duct as a function of pacemaker cells for the spontaneous rhythmic pancreatic duct contractions, and ICCs around the large blood vessels most likely affected vessel wall rhythmicity. Although the exact function of these cells is not clear, the discovery of pancreatic ICC supports the diagnosis of an EGIST arising solely from the pancreas. Although the above studies have demonstrated the existence of ICCs in the pancreas, they did not reveal the different distribution of ICCs among the different locations of pancreas. Thus, the different distribution of pancreatic GISTs in respect to locations remains further investigations.

In our present study, 14 tumors displayed cystic mass (35.9%) and 8 tumors showed mixed mass (20.5%). It is well known that cystic lesions of the pancreas are usually pseudocysts, related to chronic pancreatitis. Cystic tumors of the pancreas most commonly corresponds to serous microcystic adenoma, mucinous cystic tumor, intraductal mucinous tumor, and solid pseudopapillary tumor, while less commonly to cystic endocrine tumors, cystic teratomas, cystic metastasis, and lymphagiomas.48 Although very rare in the pancreas, GISTs should be considered in the differential diagnosis of cystic pancreatic masses. Correct diagnosis of cystic pancreatic GISTs is very difficult before operation. Computed tomography (CT) and endoscopic ultrasound guided fine needle aspiration (EUS-FNA) are usually used to confirm the diagnosis of pancreatic lesions. The accuracy of CT to predict malignant versus benign cystic lesion of the pancreas ranges between 76% and 82%, and the accuracy of CT determination of the histopathologic diagnosis of a pancreatic cystic lesion is <50%.49 EUS-FNA may be helpful for the diagnosis of pancreatic lesions.50 However, the accuracy of EUS-FNA of a cystic lesion is much lower than that of solid mass, because successful diagnosis of GIST using FNA depends on the adequacy of the specimen.

It is important to differentiate between pancreatic and duodenal GISTs adjacent to the pancreas immediately. The proximity of the C-loop of the duodenum to the pancreatic head may make it difficult to distinguish the origin of the GISTs by imaging examination alone. Given its ability to distinguish the different layers of the gastrointestinal tract with high accuracy, EUS is the most successful method at differentiating GISTs origin between the duodenum and head of pancreas.32,35

In our present study, nearly 60% of the pancreatic GISTs displayed cystic or mixed imaging features. Thus, we investigated the correlation between imaging features and clinicopathologic features. We found that the imaging features were correlated with tumor size and histologic type. All the pancreatic GISTs with cystic or mixed imaging features were classified as high risk category in our present study. This may due to the positive correlation between the cystic changes and tumor size. Interestingly, most of the solid pancreatic GISTs displayed spindle cell morphology. However, only half of the tumors with cystic or mixed features displayed spindle cell morphology. Whether there is a direct correlation between epithelioid cell morphology and cystic change needs further investigations.

It is reported that tumor size and mitotic index are the best prognostic indicators for determining the malignant potential of GISTs.51 In our present study, mitotic index was the only risk factor for the prognosis of pancreatic GISTs by univariate analysis. As a result, the multivariate analysis of independent risk factor for prognosis was not necessary in our present study. This may attribute to the limited sample size of pancreatic GISTs.

Complete surgical resection with negative microscopic margins is the standard treatment used to address GISTs.52 It is well known that extended resection, including lymphadenectomy is unnecessary, because lymph node metastases are rare (prevalence is about 1%)53 and skip metastases have never been reported. Although variety of surgical procedures have been reported in the literature, surgical resections depends upon the location of pancreatic GISTs. GISTs of the pancreaticoduodenal complex present many technical challenges because of the anatomy of the region. In this situation, pancreaticoduodenectomy (Whipple procedure) is demonstrated to be feasible.15 Duodenum preserving pancreatic head resection or simple tumor excision can also be applied, if the tumor is small with clear boundary or the patient cannot tolerate pancreaticoduodenectomy.13 Pancreatic body and tail resection with splenectomy or partial resection of the pancreas could be performed if the tumor is located in the body or tail of pancreas. Gastrectomy, segmental bowel resection and hemicolectomy could also be performed depending on the location of pancreatic GISTs.42

Besides tumor size and mitotic index, tumor location is also one of the recurrent risk factors for GISTs after radical resection.54 However, the modified NIH risk classification system distinguishes only gastric from nongastric tumors,45 and the prognostic characteristics of pancreatic GISTs are not discussed. Thus, the prognosis of pancreatic and gastric GISTs were compared in our study. We found that the DFS of pancreatic GISTs was significantly worse than that of gastric GISTs, while the DSS was comparable between the 2 groups. Multivariate analysis showed that location was an independent prognostic factor for DFS between pancreatic and gastric GISTs, but not for DSS.

There are some limitations in our present study. First, it is a retrospective analysis. Therefore, completeness of the data is limited. Second, the sample size of pancreatic GISTs was not large enough, which will result in sampling error. Third, due to the limited sample size of duodenal, small intestinal and rectal GISTs in our center, we could not compare the clinicopathologic features and prognosis of pancreatic with nongastric GISTs.

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CONCLUSIONS

The most common location was head of pancreas. The majority of pancreatic GISTs exceeded 5 cm in diameter, displayed cystic or mixed imaging features, and were high risk. The imaging features were correlated with tumor size and histologic type. Mitotic index was the only risk factor for DFS of pancreatic GISTs. Pancreatic GISTs differed significantly from gastric GISTs in respect to clinicopathologic features. The DFS of pancreatic GISTs was worse than that of gastric GISTs.

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Keywords:

gastrointestinal stromal tumor; pancreas; feature; prognosis

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