Analysis of 100 consecutive cases of resectable pancreatic neuroendocrine neoplasms: clinicopathological characteristics and long-term outcomes

Abstract

The incidence rate of pancreatic neuroendocrine neoplasms (pNENs) has increased rapidly in recent years. However, the clinicopathological characteristics of pNENs are poorly understood. Medical records of patients who underwent surgery and were confirmed as pNENs by pathological examination from January 2003 to February 2015 in Qilu Hospital were reviewed retrospectively. A total of 100 patients, 36 males and 64 females, were included with a mean operation age of 46.26±13.41 years. Among the 100 cases, 76 had insulinomas and 24 had non-functional pNENs. Tumor size ranged from 0.5 cm to 9 cm, and the mean size was 2.20±1.40 cm. The percentages of TNM stages I, II, III, and IV tumors were 89.0%, 8.0%, 0.0%, and 3.0%, respectively. Based on the WHO classification, pNENs were classified into three grades: G1, G2, and G3. G1, G2, and G3 tumors were confirmed in 72.9%, 23.7%, and 3.4% patients, respectively. The positive rates of CgA and Syn immunohistochemical staining were 94.5% (69/73) and 100% (74/74), respectively. Compared with insulinoma, non-functional pNENs have larger tumor sizes, more advanced TNM staging, a higher Ki-67 index, and a higher rate of liver metastasis (P<0.05). In conclusion, pNENs are heterogeneous tumors with varying clinical manifestations, diverse tumor biological characteristics, and different prognoses. Non-functional pNENs present a more aggressive behavioral model and have poorer prognosis than functional pNENs.

Keywords

pancreatic neuroendocrine neoplasms / clinicopathological characteristic / Ki-67 / liver metastasis / outcomes

Introduction

Pancreatic neuroendocrine neoplasms (pNENs) are a group of heterogeneous neoplasms that are presumed to originate from enterochromaffin-like cells, also known as islets of Langerhans [ 1, 2]. The incidence rate of pNENs is quite low, making them rare tumors, and they account for only 1%–4% of all pancreatic neoplasms. Nevertheless, their incidence rate has increased rapidly in recent years to about 1/100 000 per year [ 3– 5]. This phenomenon may be partially explained by the improved radiographic techniques and physicians’ increased knowledge about pNENs [ 6, 7]. As heterogeneous tumors, pNENs can be divided into two groups based on the ability to secrete functionally active hormones: functional pNENs and non-functional pNENs. These two different groups of tumors have significant differences in clinical manifestations, biological behavior, and prognosis [ 8– 10]. Data available on the clinicopathological characteristics and prognosis of pNENs are limited because of its low incidence rate, especially in the Asian population. In this retrospective study, we collected and analyzed the clinicopathological data of 100 consecutive patients who underwent pNENs resection. The study aimed to illustrate the clinicopathological characteristics and prognosis of these “rare” tumors.

Patients and methods

Patients included in this retrospective study underwent surgery at the Department of General Surgery, Qilu Hospital from January 2003 to February 2015, and were confirmed as pNENs by pathological examination.

This 12-year retrospective study was conducted in Qilu Hospital of Shandong University. This study was approved by the authors’ institutional review board and performed in accordance with the ethical standards and the Declaration of Helsinki. Written informed consent was obtained from all subjects. The diagnosis for pNENs was based on the pathological morphological results and immunohistochemical (IHC) results of surgical resected specimens or intraoperative biopsy by experienced pathologists. Medical records were reviewed independently by two authors (Y.G. Cheng and H.X. Zhan). Demographic data, clinicopathological characteristics, surgical approaches, and histopathological reports were collected and analyzed. Follow-up data were acquired from hospital records and supplemented with information collected from telephone interview with patients. According to their clinical manifestations and symptoms of hormonal excess, patients were divided into two groups: functional pNENs (functional group) and non-functional pNENs (non-functional group). pNENs were classified into three grades according to the WHO classification standard: G1 (mitotic count<2/10 high power fields [HPF] and Ki-67 index<3%), G2 (mitotic count= 2/10–20/10 HPF and/or Ki-67 index of 3%–20%), and G3 (mitotic count>20/10 HPF and/or a Ki-67 index>20%)[ 11].

Statistical analysis was conducted using SPSS v.16.0 software (SPSS Inc., Chicago, IL, USA). The mean value and median reflected central tendency of data, as well as the quantitative normally distributed data, were expressed as mean value±standard deviation (SD). The median was used to express non-normally distributed data. “Listwise Deletion” method was used to handle missing data in the analysis. Student’s t-test and ANOVA were used to compare quantitative variables. Chi-square test and Fisher’s exact test were adopted to compare categorical variables. P<0.05 was considered as statistically significant.

Results

General information

From January 2003 to February 2015, a total of 100 patients underwent surgery and were diagnosed as pNENs at the Department of General Surgery, Qilu Hospital (Fig. 1). Among the patients, 36 were males and 64 were females (1:1.77) (Table 1), and their mean operation age was 46.26±13.41 years (range: 14–77) (Fig. 2). The median duration of disease before diagnosis was 15.0 months (range: 0.1–192 months, 24.0 months for functional pNENs and 3.0 months for non-functional pNENs). Abdominal ultrasonography, computed tomography (CT), magnetic resonance imaging (MRI), and endoscopic ultrasonography (EUS) were the most commonly used imaging methods for preoperative localization of tumor. EUS provided the best sensitivity (100%, 21/21) (Table 2).

Clinicopathological characteristics

Among the 100 patients, 76 had functional pNENs (all of which were insulinomas), and 24 had non-functional pNENs. Single lesion was confirmed in 95 cases (95%), and 4 functional pNENs patients and 1 non-functional pNEN patient had multiple lesions (2–8 tumors). Average tumor size was 2.20±1.40 cm. Non-functional pNENs were much larger than functional pNENs (3.60 cm vs. 1.70 cm, P<0.001) (Table 3). Table 4 shows the location of these tumors: 10 cases were located in the head of the pancreas (10%), 24 in the uncinate process (24%), 12 in the neck (12%), 25 in the body (25%), 13 in the body–tail junction (13%), and 11 in the tail of the pancreas (11%). Five cases had multiple lesions. Lesions distributed in any part of the pancreas were confirmed in 2 cases.

According to the American Joint Committee on Cancer (AJCC) staging criteria [ 12], the percentages of patients staged as TNM IA, IB, IIA, IIB, IIIA, IIIB, and IV tumors were 63.0%, 26.0%, 8.0%, 0.0%, 0.0%, and 3.0%, respectively. All insulinoma patients were at stage TNM I. Three non-functional pNENs patients had liver metastasis and were at stage TNM IV. The non-functional group had greater incidence of later-stage pNENs than the functional group (P<0.001) both according to the AJCC TNM and ENETS TNM staging systems [ 13] (Table 5). For IHC staining, 96.2% surgical resected specimens (51/53) were CgA-positive, and all patients were positive for Syn protein expression (53/53) (Table 6, Fig. 3).

Data on Ki-67 proliferative index and mitotic count were available in 59 patients. Based on the WHO classification, the percentages of G1, G2, and G3 tumors were 72.9% (43/59), 23.7% (14/59), and 3.4% (2/59). Compared with functional tumors, more non-functional tumors were classified in the G2 and G3 groups (35.0% vs. 23.1%, P = 0.021). Ki-67 index was much higher in non-functional than in functional pNENs (4.3% vs. 2.1%, P = 0.043) (Table 5).

Surgical procedures and postoperative recovery

All 100 patients received surgical treatment by intact removal of tumors and liver metastasis discovered during pre-surgery and surgery. Surgical procedures included pancreatic tumor enucleation (67.0%, 67/100), distal pancreatectomy, and spleen-preserved (19.0%, 19/100), distal pancreatectomy plus spleen resection (5.0%, 5/100), central pancreatectomy plus distal pancreas–jejunum anastomosis (6.0%, 6/100), and pancreatoduodenectomy (3.0%, 3/100). Among the patients, 26 patients received laparoscopic surgical procedures (Table 7).

All patients survived during the perioperative period, and the average postoperative hospitalization time was 17.39±13.99 days (6–110 days). Postoperative complication included pancreatic leakage (36.0%, 36/100), intra-abdominal hemorrhage (3.0%, 3/100), intra-abdominal infection (4.0%, 4/100), incomplete intestinal obstruction (3.0%, 3/100), high platelet levels (3.0%, 3/100), and pancreatic pseudocyst (1.0%, 1/100). According to the pancreatic fistula grading standard of the International Study Group on Pancreatic Fistula (ISGPF), the percentages of A, B, and C grade were 36.1% (13/36), 58.3% (21/36), and 5.6% (2/36), respectively. All patients were successfully discharged after appropriate treatment.

Follow-up and survival

The median follow-up period was 38 months (range: 3–126 months). During this period, 19 patients were lost to follow-up, so that the follow-up rate was 81.0%. At the last follow-up, 2 patients (2.5%) died of liver metastasis after surgery. The overall survival rates over 1, 3, and 5 years were 100%, 97.7%, and 96.8%, respectively (Fig. 4). Tumor recurrence occurred in 4 cases (9, 12, 48, and 78 months after first operation); reoperations were performed on these cases. Liver metastasis after surgery was discovered in 4 patients, 2 of whom died from it. A third patient suffered from liver metastasis 9 months after surgery, underwent radiofrequency ablation, and was free of metastasis in the follow-up period. The last patient underwent two courses of transcatheter arterial chemoembolization, after which no liver metastasis was detected in the follow-up period of about 17 months.

Discussion

Our knowledge of the molecular characteristics, diagnosis, and treatment of pNENs increased greatly in the last decade. Various guidelines [ 14– 20] from different academic organizations, such as ENETS, NANETS, NCCN, and WHO, have been applied in clinical practice. Diagnosis, classification, pathological staging, surgical management, and systematic treatment of pNENs have been standardized, thus resulting in the development of diagnosis and surgical treatment. However, because of the heterogeneity and distinct origin of pNENs, no ideal biomarker is able to distinguish the malignant pNENs from benign ones.

The WHO 2010 classification has been widely used for evaluating the level of differentiation and malignancy of pNENs. This classification is based on the concept that all NETs have malignant potential, thus abandoning the division of benign NETs, malignant NETs, and tumors of uncertain malignant potential [ 18]. It classifies tumors according to grade and stage. Ki-67 index and mitotic count are two important parameters of this classification system. In this retrospective study, functional pNENs patients had lower Ki-67 index and mitotic count than non-functional pNENs, and thus the percentages of G2 and G3 were much higher in non-functional pNENs. This result is consistent with the different biological behaviors of insulinomas and non-functional pNENs. Non-functional pNENs usually have a larger tumor size, higher proliferation capacity, more aggressive behavior, and more advanced TNM stage than the functional ones. Our findings agree with the heterogeneous behavior of pNENs. Although Ki-67 index is considered important in describing tumor behavior and assessing the risk of recurrence of the disease, setting a cut-off value for Ki-67 to grade pNENs remains controversial. Some researchers showed differences in Ki-67 value with cut-offs at 2% and 20% between G3 and (G1+ G2) but failed to demonstrate any difference in survival between G1 and G2 patients, whereas Scarpa et al. demonstrated that Ki-67 value with cut-offs at 5% and 20% had much better prognostic value and could discern prognosis among pNENs at the same stage [ 21]. Therefore, further studies are needed to explore new biomarkers to grade and discern the tumor behavior and prognosis of pNENs. Genomics and proteome studies may be helpful for screening new biomarkers.

In the present study, many TNM staging systems for pNENs were applied to evaluate prognosis and mortality risk and to provide important information on treatment after operation. ENETS TNM system and UICC/AJCC/WHO 2010 TNM system are the most frequently used in clinical practice. These two staging systems differ from each other in several aspects [ 22, 23], which have been validated by multiple previous studies [ 21– 25]. The largest study that compared these two staging systems included 1072 patients, and it concluded that the UICC/AJCC/WHO 2010 TNM staging system showed a large 95% confidence intervals for each stage, thus indicating inaccurate predictive ability. Conversely, the ENETS TNM staging system was more accurate than and superior to the UICC/AJCC/WHO 2010 TNM staging system. Our results support the superiority of the ENETS TNM staging system.

The measurement of the secretory products of pNENs is helpful for initial diagnosis, assessment of treatment efficacy, and evaluation of prognosis. Moreover, specific hormones related to functional pNENs, such as insulin, gastrin, glucagon, and other circulating secretory products, are also applied to pNENs diagnosis. CgA, Syn, NSE, and pancreatic polypeptide offer high sensitivity in pNEN diagnosis, especially in non-functional pNENs [ 18– 20, 26– 28]. In addition to circulating serum markers, IHC staining of proteins in surgically removed samples is also helpful for discriminating pNENs from other pancreatic neoplasms (e.g., pancreatic acinar carcinoma and solid pseudopapillary neoplasm of pancreas). In our study, IHC staining of CgA and Syn had positivity rates of 96.2% and 100% among surgically resected samples, thus proving its high sensitivity. These proteins are suggested for use in the IHC stain testing of surgically resected samples.

We acknowledge some limitations in our study. The major limitation is that selection bias is inevitable because of the retrospective nature of the study. Functional pNENs accounted for 76% of all patients, whereas non-functional pNENs accounted for only 24%, thus the results may not reflect the comprehensive natural biological behavior of pNENs. Moreover, some important data were not recorded and could not be analyzed because of the long study period and the update in the classification system (e.g., WHO classification). Studies with larger sample sizes and multi-center data collection may be helpful to further elucidate the clinicopathological characteristics of pNENs.

In conclusion, pNENs are heterogeneous tumors with diverse clinical manifestations, tumor biological characteristics, and prognoses. Non-functional pNENs present a more aggressive behavioral model and have poorer prognosis than functional pNENs. As pNENs have a much better prognosis than pancreatic ductal adenocarcinoma, treatment strategies should be more aggressive to improve long-term survival in patients with pNENs.

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