Gastroenterology Research and Practice

Gastroenterology Research and Practice / 2020 / Article

Research Article | Open Access

Volume 2020 |Article ID 1946156 | https://doi.org/10.1155/2020/1946156

Zhe Wang, Feng Cao, Yupeng Zhang, Yu Fang, Fei Li, "Risk Factors of Lymph Node Metastasis in Patients with Pancreatic Neuroendocrine Tumors (PNETs)", Gastroenterology Research and Practice, vol. 2020, Article ID 1946156, 10 pages, 2020. https://doi.org/10.1155/2020/1946156

Risk Factors of Lymph Node Metastasis in Patients with Pancreatic Neuroendocrine Tumors (PNETs)

Academic Editor: Vincenzo Pilone
Received15 Mar 2020
Revised25 May 2020
Accepted29 Jun 2020
Published29 Sep 2020

Abstract

Background. The prognostic value of lymph node metastasis in patients with PNETs is controversial. Understanding the effect of lymph node metastasis on prognosis in pancreatic neuroendocrine tumors is helpful for surgery and follow-up. The purposes of this study are to identify predictors of lymph node metastasis among patients with PNETs and determine its prognostic associations. Methods. A retrospective analysis of the surveillance, epidemiology, and end results (SEER) database was performed. Patients with PNETs that underwent surgery and pathologic nodal staging were identified. Logistic regression and Cox regression were performed to identify independent predictors and prognostic factors, respectively. Results. Of 1956 patients (age: years, 53.3% males), 748 (38.2%) had lymph node metastasis. On multivariable analysis, tumor located in pancreas head, distant metastasis, and poorly differentiated, undifferentiated, and unknown differentiated histology grades were three independent risk factors of lymph node metastasis. In the entire cohort, lymph node metastasis indicated a worse overall survival (HR: 1.48, 95% CI: 1.17-1.88, ) and disease-specific survival (HR: 1.87, 95% CI: 1.41-2.48, ) on multivariable analysis. Lymph node metastasis was associated with worse overall (HR: 1.45, 95% CI: 1.08-1.93, ) and disease-specific survival (HR: 2.13, 95% CI: 1.48-3.05, ) in patients without distant metastasis on multivariate analysis. Lymph node metastasis was also independently associated with worse disease-specific survival among patients in well differentiation (HR: 2.16, 95% CI: 1.35-3.46, ) and moderately differentiation (HR: 2.67, 95% CI: 1.28-5.56, ) groups on multivariate analysis. Conclusions. Tumor located in pancreas head, distant metastasis, and poorly differentiated, undifferentiated, and unknown differentiated histology grades were three independent risk factors for lymph node metastasis. Lymph node metastasis was an independent prognostic factor of worse OS and DSS in patients with tumor located in pancreas head. Lymph node metastasis was an independent prognostic factor of worse OS and DSS in patients without distant metastasis. Lymph node metastasis was an independent prognostic factor of worse DSS in well differentiation and moderately differentiation groups.

1. Introduction

The neuroendocrine tumors (NETs) originate from neuroendocrine cells and may occur in many organs, including the lung, gastrointestinal tract, and pancreas. NETs occur in approximately 6/100,000 [1]. Among them, gastroenteropancreatic NETs (GEP-NETs) account for 65-75% of the whole body NETs. Pancreatic NETs (PNETs) comprise approximately half of the GEP-NETs [2] and account for approximately <3% of all pancreatic malignancies. As a rare pancreatic neoplasm with an annual incidence of 0.19/100,000-0.32/100,000 [3], the incidence of PNETs has been rising in the United States over the past several decades [4].

The natural history of PNETs is highly variable, with some tumors showing indolent behavior but others displaying an aggressive course, with local invasion and distant metastasis [5]. Several staging systems have been developed to better stratify prognosis in patients with PNETs. The World Health Organization staging system incorporates mitotic count and Ki-67 index to separate patients into three categories [6]. The eighth edition of the American Joint Committee on Cancer (AJCC) tumor–node–metastasis staging system includes primary tumor size, presence of lymph node metastasis on pathologic examination, and presence of distant metastases [7]. Lymph node status is particularly important in PNETs staging systems, because the presence of lymph node metastasis would render a patient stage III according to both the AJCC and European Neuroendocrine Tumor Society staging (ENETS) systems [8]. The prognostic significance of lymph node metastasis in PNETs is controversial. Some researchers have reported a significant association between lymph node metastasis and survival [915], while others showed no association [1619]. Lymph node metastasis is an important marker of malignancy and, as such, may influence the type and extent of PNETs surgical management. The purposes of this study are to identify predictors of lymph node metastasis among patients with PNETs and determine its prognostic associations.

2. Methods

A retrospective analysis of the National Cancer Institute’s SEER database was performed for patient diagnosed between 2004 and 2016. The SEER database is a comprehensive database that collects information on several clinical and pathologic aspects of multiple cancers and is approximated to encompass 28% of the US population. Pancreatic neuroendocrine tumors were identified using their ICD-O-3 codes (8013/3, 8150/3, 8151/3, 8152/3, 8153/3, 8155/3, 8156/3, 8240/3, 8241/3, 8242/3, 8243/3, 8245/3, 8246/3, 8247/3, 8248/3, and 8249/3). Patients without positive histological diagnosis and those that did not undergo surgical resection were excluded. Patients without available information regarding their lymph node status were also excluded. Only patients that met criteria for pathologic nodal staging (PN staging) were included based on the SEER variable CS lymph Nodes Eval (CS Lymph Nodes Eval code 3 and code 6). In this way, patients without pathological nodal staging were excluded from the analysis. A flowchart demonstrating patient selection can be viewed in Figure 1. All tumors were primary tumors. The study was exempted from Institutional Review Board approval, due to SEER’s use of unidentifiable patient information.

3. Statistical Analysis

Univariate and multivariable logistic regressions were performed to ascertain the possible factors associated with the presence of lymph node metastasis. Univariate and multivariable analyses using the Cox proportional hazards model were performed to ascertain the prognostic role of nodal metastasis, with both overall survival (OS) and disease-specific survival (DSS) as endpoints. All statistical tests used two-tailed values, and 0.05 was set as the threshold for significance. Statistical analysis was performed using the IBM SPSS Statistics v.22.0.0 (IBM Corp, Armonk, NY).

4. Results

Overall, 1956 patients were identified, of which 748 patients (38.2%) had lymph node metastasis. The median number of lymph node examined was 10 (mean ), and the median number of metastatic lymph nodes was 2 (mean ). Most tumors were located in the body and tail of pancreas (1016 (51.9%)), followed by the head of pancreas (632 (32.3%)) and the overlapping lesion and other specified parts of pancreas (308 (15.7%)). Most patients were males (1043 (53.3%)) and 301 (15.4%) patients had synchronous distant metastasis at diagnosis. Patients were followed for a median period of 49.1 months (range 0-155 months). Detailed demographic, clinical, and pathologic features of the study cohort are listed in Table 1.


No. of patients
()
Patients with LN metastases
()

Age at diagnosis years years
Sex
 Male1043 (53.3%)401 (53.6%)
 Female913 (46.7%)347 (46.4%)
Race
 White1289 (65.9%)510 (68.2%)
 Black223 (11.4%)94 (12.6%)
 Hispanic249 (12.7%)85 (11.4%)
 Asian168 (8.6%)51 (6.8%)
 Other27 (1.4%)8 (1.1%)
Marital status
 Unmarried607 (31.0%)233 (31.1%)
 Married1251 (64.0%)482 (64.4%)
 Unknown98 (5.0%)33 (4.4%)
Insurance status
 Uninsured47 (2.4%)17 (2.3%)
 Insured1689 (86.3%)619 (82.8%)
 Unknown220 (11.2%)112 (15.0%)
Tumor location
 Head632 (32.3%)295 (39.4%)
 Body and tail1016 (51.9%)332 (44.4%)
 Overlapping111 (5.7%)46 (6.1%)
 Other197 (10.1%)75 (10.0%)
Tumor size
 <2 cm526 (26.9%)75 (10.0%)
 2 cm-4 cm708 (36.2%)283 (37.8%)
 >4 cm718 (36.7%)389 (52.0%)
 Unknown4 (0.2%)1 (0.1%)
M stage
 M01644 (84.0%)521 (69.7%)
 M1301 (15.4%)221 (29.5%)
 Mx11 (0.6%)6 (0.8%)
Histology gradea
 Well differentiated1234 (63.1%)401 (53.6%)
 Moderately differentiated319 (16.3%)127 (17.0%)
 Poorly differentiated109 (5.6%)84 (11.2%)
 Undifferentiated24 (1.2%)18 (2.4%)
 Unknown270 (13.8%)118 (15.8%)

aHistology grade was based on WHO classification of tumors 4th edition.
4.1. Risk Factors of Lymph Node Metastasis

On univariate analysis, race (), tumor location (), tumor size (), M stage of the disease (), and histology grade () were associated with the presence of lymph node metastasis. These variables were then included in multivariable analysis. Finally, patients with tumor located in pancreas head, distant metastasis, and poorly differentiated, undifferentiated, and unknown differentiated histology grades were three independent risk factors associated with the diagnosis of the patient lymph node metastasis (Table 2).


UnivariateMultivariable
OR
(95% CI)
valueAdjusted OR
(95% CI)
value

Agea0.99 (0.98-1.01)0.163
Sex0.867
 MaleReference
 Female1.02 (0.83-1.25)
Race0.0340.058
 WhiteReferenceReference
 Black1.24 (0.91-1.70)1.28 (0.92-1.78)0.144
 Hispanic0.80 (0.59-1.10)0.75 (0.55-1.04)0.081
 Asian0.64 (0.44-0.94)0.63 (0.42-0.92)0.018
 Other0.67 (0.28-1.62)0.80 (0.32-2.00)0.629
Marital status0.420
 UnmarriedReference
 Married1.06 (0.85-1.33)
 Unknown0.78 (0.48-1.28)
Insurance status0.165
 UninsuredReference
 Insured1.33 (0.68-2.57)
 Unknown1.74 (0.85-3.58)
Tumor location<0.001<0.001
 HeadReferenceReference
 Body and tail0.54 (0.43-0.67)0.54 (0.43-0.68)<0.001
 Overlapping0.69 (0.43-1.08)0.70 (0.44-1.13)0.144
 Other0.68 (0.48-0.97)0.69 (0.48-0.99)0.045
Tumor sizea1.01 (1.00-1.05)0.0081.03 (1.00-1.06)0.347
M stage<0.001<0.001
 M0ReferenceReference
 M15.15 (3.85-6.90)4.09 (3.04-5.51)<0.001
 Mx2.77 (0.80-9.59)2.31 (0.65-8.25)0.197
Histology grade<0.001<0.001
 Well differentiatedReferenceReference
 Moderately differentiated1.11 (0.84-1.46)0.95 (0.72-1.26)0.728
 Poorly differentiated5.12 (3.14-8.35)3.90 (2.39-6.36)<0.001
 Undifferentiated3.84 (1.43-10.33)4.18 (1.51-11.57)0.006
 Unknown1.33 (0.98-1.79)1.38 (1.01-1.87)0.041

aContinuous variables.
4.2. Prognostic Value of Lymph Node Metastasis

Seven hundred and forty-eight patients with lymph node metastasis had a median overall survival of 45 months, while median overall survival was 41 months in patients without lymph node metastasis. Excluding 301 (15.4%) patients with distant metastasis, the median overall survival time for remaining 1655 (84.6%) patients with lymph node metastasis was 42 months, and the median overall survival of patients without lymph node metastasis was 40 months.

On univariate analysis, lymph node metastasis ( vs. months, ), older age (<40 years: months, 40-59 years, months, 60-79 years: months, and ≥80 years: months, ), male ( vs. months, ), unmarried (unmarried months, married: months, ), uninsured (uninsured: months, insured: months, ), tumor located in the pancreas head (head: months, body and tail: months, and overlapping: months, ), large tumor size (<2 cm: months, 2-4 cm: months, and >4 cm: months, ), distant metastasis ( vs. months, ), and lower levels of differentiation (well differentiated: months, moderately differentiated: months, poorly differentiated: months, and undifferentiated: months, ) were associated with worse OS. While, on multivariable analysis lymph node metastasis was still an independent factor indicated worse OS (HR: 1.48, 95% CI: 1.17-1.88, ) (Table 3).


UnivariateMultivariable
HR
(95% CI)
valueAdjusted HR
(95% CI)
value

Age<0.001<0.001
 <40ReferenceReference
 40-591.42 (0.94-2.15)0.0421.37 (0.90-2.08)0.014
 60-791.84 (1.22-2.77)0.0032.06 (1.36-3.12)0.001
 ≥803.48 (1.92-6.33)<0.0013.30 (1.79-6.06)<0.001
Sex0.0060.003
 MaleReferenceReference
 Female0.74 (0.60-0.92)0.0060.71 (0.57-0.89)0.003
Race0.451
 WhiteReference
 Black0.92 (0.65-1.30)0.634
 Hispanic0.90 (0.64-1.26)0.523
 Asian0.68 (0.43-1.06)0.086
 Other0.65 (0.21-2.03)0.456
Marital status0.0220.050
 UnmarriedReferenceReference
 Married0.86 (0.68-1.07)0.0170.76 (0.60-0.96)0.022
 Unknown0.66 (0.37-1.17)0.0160.65 (0.37-1.17)0.149
Insurance status<0.0010.005
 UninsuredReferenceReference
 Insured0.53 (0.30-0.95)0.0330.51 (0.28-0.92)0.026
 Unknown0.92 (0.50-1.70)0.0800.73 (0.39-1.36)0.318
Tumor location0.0060.034
 HeadReferenceReference
 Body and tail0.67 (0.53-0.84)0.0010.71 (0.56-0.90)0.005
 Overlapping0.95 (0.61-1.49)0.8240.78 (0.49-1.23)0.284
 Other0.81 (0.57-1.15)0.2340.97 (0.68-1.39)0.871
Tumor size<0.0010.005
 <2 cmReferenceReference
 2 cm-4 cm2.38 (1.63-3.47)<0.0011.72 (1.16-2.53)0.007
 >4 cm3.61 (2.52-5.17)<0.0012.01 (1.37-2.96)<0.001
 Unknown0.9990.941
M stage<0.001<0.001
 M0ReferenceReference
 M13.58 (2.86-4.45)<0.0012.61 (2.06-3.31)<0.001
 Mx0.98 (0.24-3.96)0.9790.87 (0.21-3.55)0.849
Histology grade<0.001<0.001
 Well differentiatedReferenceReference
 Moderately differentiated1.41 (1.01-1.95)0.4011.13 (0.81-1.57)0.474
 Poorly differentiated6.07 (4.51-8.16)<0.0013.56 (2.62-4.84)<0.001
 Undifferentiated7.81 (4.42-13.81)<0.0015.80 (3.22-10.45)<0.001
 Unknown1.78 (1.35-2.35)<0.0011.46 (1.10-1.95)0.010
Lymph node metastasis<0.001<0.001
 No metastasisReferenceReference
 Metastasis2.55 (2.05-3.17)<0.0011.48 (1.17-1.88)0.001

On univariate analysis, lymph node metastasis ( vs. months, ), older age (<40 years: months, 40-59 years, months, 60-79 years: months, and ≥80 years: months, ), male ( vs. months, ), unmarried (unmarried months, married: months, ), uninsured (uninsured: months, insured: months, ), tumor located in the pancreas head (head: months, body and tail: months, and overlapping: months, ), large tumor size (<2 cm: months, 2-4 cm: months, and >4 cm: months, ), distant metastasis ( vs. months, ), and lower levels of differentiation (well differentiated: months, moderately differentiated: months, poorly differentiated: months, and undifferentiated: months, ) were associated with worse DSS. However, on multivariable analysis, lymph node metastasis was also an independent factor indicated worse DSS (HR: 1.87, 95% CI: 1.41-2.48, ) (Table 4; Figure 2).


UnivariateMultivariable
HR
(95% CI)
valueAdjusted HR
(95% CI)
value

Age0.0460.012
 <40ReferenceReference
 40-591.31 (0.85-2.03)0.2261.27 (0.81-1.99)0.303
 60-791.54 (0.99-2.38)0.0561.76 (1.12-2.75)0.013
 ≥802.38 (1.16-4.85)0.0182.16 (1.04-4.48)0.038
Sex0.0140.009
 MaleReferenceReference
 Female0.74 (0.58-0.94)0.0140.69 (0.54-0.89)0.004
Race0.584
 WhiteReference
 Black0.99 (0.68-1.44)0.962
 Hispanic0.81 (0.54-1.21)0.306
 Asian0.70 (0.43-1.15)0.162
 Other0.84 (0.27-2.61)0.757
Marital status0.0160.040
 UnmarriedReferenceReference
 Married0.81 (0.63-1.04)0.0100.72 (0.55-0.94)0.016
 Unknown0.63 (0.33-1.20)0.0160.62 (0.32-1.21)0.163
Insurance status<0.0010.007
 UninsuredReferenceReference
 Insured0.54 (0.28-1.06)0.0750.52 (0.26-1.04)0.065
 Unknown1.08 (0.54-2.16)0.8360.80 (0.39-1.63)0.533
Tumor location0.0110.064
 HeadReferenceReference
 Body and tail0.69 (0.50-0.84)0.0010.71 (0.54-0.93)0.012
 Overlapping0.98 (0.59-1.61)0.9250.81 (0.49-1.36)0.429
 Other0.79 (0.53-1.18)0.2541.01 (0.67-1.53)0.951
Tumor size<0.0010.014
 <2 cmReferenceReference
 2 cm-4 cm3.05 (1.90-4.90)<0.0011.90 (1.17-3.11)0.010
 >4 cm5.02 (3.18-7.91)<0.0012.23 (1.37-3.62)0.001
 Unknown0.9480.940
M stage<0.001<0.001
 M0ReferenceReference
 M14.89 (3.85-6.21)<0.0013.21 (2.47-4.16)<0.001
 Mx1.44 (0.36-5.81)0.6111.21 (0.30-4.95)0.792
Histology grade<0.001<0.001
 Well differentiatedReferenceReference
 Moderately differentiated1.73 (1.20-2.50)0.0641.32 (0.91-1.92)0.144
 Poorly differentiated8.45 (6.11-11.68)<0.0014.64 (3.31-6.49)<0.001
 Undifferentiated10.61 (5.81-19.39)<0.0017.65 (4.10-14.27)<0.001
 Unknown2.15 (1.56-2.95)<0.0011.69 (1.21-2.36)0.002
Lymph node metastasis<0.001<0.001
 No metastasisReferenceReference
 Metastasis3.63 (2.80-4.72)<0.0011.87 (1.41-2.48)<0.001

Among patients with lymph node metastasis, a higher number of positive lymph nodes was related to worse OS (HR 1.01, 95% CI: 1.00-1.02, ) and DSS (HR 1.01, 95% CI: 0.99-1.02, ) on univariate analysis.

4.3. Subgroup Analysis of Tumor Location, Distant Metastasis, and Histology Grade

Subgroup analysis of tumor location, distant metastasis, and histology grade were executed to ascertain whether the diagnosis of lymph node metastasis was independent prognostic factor in these groups of patients.

According to the tumor location, 632 (32.3%) patients have their tumor located in the pancreas head. Among this subgroup, 295 (46.7%) patients had lymph node metastasis. On univariate analysis, lymph node metastasis was related to both worse OS (HR: 2.46, 95% CI: 1.73-3.51, ) and DSS (HR: 2.91, 95% CI: 1.93-4.40, ). Also, the result was worse OS (HR: 1.83, 95% CI: 1.23-2.70, ) and DSS (HR: 2.03, 95% CI: 1.29-3.22, ) on multivariate analysis. Among the 1324 (67.7%) patients whose tumor is located in the pancreas body, tail, overlapping, and other parts, lymph node metastasis was related to worse OS (HR: 2.48, 95% CI: 1.88-3.28, ) and DSS (HR: 3.97, 95% CI: 2.83-5.55, ) on univariate analysis. And, the result was worse OS (HR: 1.36, 95% CI: 0.99-1.87, ) and DSS (HR: 1.92, 95% CI: 1.32-2.80, ) on multivariate analysis.

In the subgroup analysis of 301 (15.4%) patients with distant metastasis, lymph node metastasis was related to worse OS (HR: 1.52, 95% CI: 0.99-2.33, ) but did not include worse DSS (HR: 1.41, 95% CI: 0.92-2.16, ) on univariate analysis. The result of OS (HR: 1.54, 95% CI: 0.98-2.41, ) and DSS (HR: 1.42, 95% CI: 0.90-2.24, ) on multivariate analysis was not statistically significant. Among 1644 (84.0%) patients without distant metastasis and 11 (0.6%) patients with unknown metastasis status, lymph node metastasis was related to both worse OS (HR: 2.15, 95% CI: 1.65-2.81, ) and DSS (HR: 3.52, 95% CI: 2.52-4.92, ) on univariate analysis. And the result was worse OS (HR: 1.45, 95% CI: 1.08-1.93, ) and DSS (HR: 2.13, 95% CI: 1.48-3.05, ) on multivariate analysis.

Consider the histology grade, there were 1234 (63.1%) patients with well-differentiated, 319 (16.3%) patients with moderately differentiated, 109 (5.6%) patients with poorly differentiated, and 24 (1.2%) patients with undifferentiated histology grades. In the well-differentiated group and moderately differentiated group, lymph node metastasis was related to both worse OS (well-differentiated group HR: 1.96, 95% CI: 1.41-2.73, ; moderately differentiated group HR: 2.13, 95% CI: 1.19-3.83, ) and DSS (well-differentiated group HR: 3.46, 95% CI: 2.27-5.29, ; moderately differentiated group HR: 2.92, 95% CI: 1.49-5.69, ) on univariate analysis. However, in poorly differentiated group and undifferentiated group, the OS (poorly differentiated group HR: 1.74, 95% CI: 0.91-3.36, ; undifferentiated group HR: 1.72, 95% CI: 0.46-6.46, ) and DSS (poorly differentiated group HR: 2.04, 95% CI: 1.00-4.16, ; undifferentiated group HR: 2.22, 95% CI: 0.48-10.19, ) were not statistically significant. On multivariate analysis, there was no statistically significant difference in OS (well-differentiated group HR: 1.33, 95% CI: 0.92-1.91, ; moderately differentiated group HR: 1.75, 95% CI: 0.93-3.31, ; poorly differentiated group HR: 1.93, 95% CI: 0.91-4.09, ; and undifferentiated group HR: 0.89, 95% CI: 0.01-7.46, ) in each differentiated subgroup. In addition, lymph node metastasis was related to worse DSS in the well-differentiated group (HR: 2.16, 95% CI: 1.35-3.46, ) and moderately differentiated group (HR: 2.67, 95% CI: 1.28-5.56, ) on multivariate analysis. Whereas, the DSS in poorly differentiated group (HR: 2.30, 95% CI: 1.01-5.23, ) and undifferentiated group (HR: 0.09, 95% CI: 0.01-7.48, ) did not achieve statistical significance on multivariate analysis.

5. Discussion

This study demonstrated that tumor located in pancreas head, distant metastasis, and poorly differentiated, undifferentiated, and unknown differentiated histology grades were three independent risk factors associated with the diagnosis of lymph node metastasis in patients with PNETs, suggesting that a high degree of suspicion for lymph node metastasis should be present in these patients. Lymph node metastasis was also identified as an independent predictor of worse overall and disease-specific survival and in patients with PNETs. And lymph node metastasis was an independent prognostic factor of worse overall survival and disease-specific survival in patients without distant metastasis. Furthermore, lymph node metastasis was an independent prognostic factor of worse disease-specific survival in patients with the well-differentiated and moderately differentiated groups.

Data concerning the incidence of lymph node metastasis in patients with PNETs is multifold. Hill and colleagues retrospectively analyzed 728 patients with PNETs and identified lymph node metastasis in only 24.9% using the SEER database [20]. The rate of lymph node metastasis that was identified in our study was 38.7%, which is in line with previously published data by Hashim and colleagues, who reported a rate of 37.6% [5]. Moreover, a 33.3% rate of lymph node metastasis was reported by the PET/CT screening imaging [21]. However, our rate of 38.7% may be an overestimation of the true incidence of lymph node metastasis due to the exclusion of low-risk patients that did not undergo nodal sampling due to a low degree of suspicion.

This study identified tumor located in pancreas head, distant metastasis, and poorly differentiated, undifferentiated, and unknown differentiated histology grades as three independent predictors of lymph node metastasis in patients with PNETs. As is well known, pancreatic resections are associated with significant morbidity, and there is interest in minimizing the impact of surgery [22]. Hence, enucleation and central pancreatectomy in selected patients, especially in those with small tumor size and tumor not close to the main pancreatic duct, could be considered as alternative management strategies to radical surgery. For instance, Tsutsumi and colleagues suggested that regional lymphadenectomy should be performed for all [23], while Jiang and colleagues suggested that regional lymphadenectomy in is not necessary [24]. Curran and colleagues found there was no lymph node metastasis in patients with in low tumor grade, so they suggested regional lymphadenectomy is unnecessary in these patients [25].

However, assessing lymph node status preoperatively by radiological examination or endoscopy cannot be accurate and facile; preoperative determination of the risk of lymph node metastases attains critical importance. Therefore, patients without known lymph node status but fulfilling these factors should be considered for pancreatectomy with regional lymphadenectomy instead of tumor enucleation or central pancreatectomy without nodal staging.

The results of this study also demonstrated that lymph node metastasis was correlated with worse OS and DSS on multivariate analysis. Moreover, the number of more lymph nodes metastasis has a certain influence on OS and DSS, which suggests that standard regional lymphadenectomy may guide accurate staging, thus having a good influence on the prognosis.

The subgroup analysis results of multivariate analysis by tumor location grouping were also worse OS and DSS. The OS and DSS were statistically significant only in PNETs patients without distant metastasis, in either univariate or multivariate analyses. This suggested that lymphadenectomy is not necessary in PNETs patients with distant metastasis. On multivariate analysis based on the grouping of tumor differentiation grade, there was no significant difference in OS among each subgroup. However, OSS only showed significant difference between the well differentiation group and the moderately differentiation group. The effect of lymph node metastasis to prognosis is controversial in patients with PNETs. Some reports have associated lymph node metastasis with a shorter OS and DSS [915]. However, several other studies have reported that lymph node metastasis has no effect on survival [1619]. It is difficult to interpret the real reasons of the contradictory results reported by different institutions. The inconsistency may be in part due to inadequate lymph node sampling rates during pancreatic resections and various measured outcome (OS, 5-year OS, DFS, DSS, etc.). Therefore, we interpreted this data to recommend that regional lymphadenectomy may be a safer choice for even low-grade patients. Meanwhile, lymph node metastasis is related to pathological features such as lymphatic, vascular, and neural invasion [26]. So, it is possible that with the extension of follow-up time, patients with high-grade PNETs will recurrence and die, so OS and DSS will become statistically significant.

There were certain several limitations for this study. The design of the study was retrospective. Large databases contain patients from different institutions and time periods. This can lead to patient selection bias, coding ,errors and missing information. Other variables, such as performance status, comorbidities, mitotic count, Ki-67 index, and surgical information (duration, blood loss, and postoperative complication), were not captured in the SEER database. In addition, there was no information on whether adjuvant therapies (chemotherapy, targeted therapy, and endocrine therapy) were given to patients with PNETs, which may have contributed to a better analysis. Despite these limitations, large database like SEER is the best database available today. We are in agreement of prospective study to better understand the risk factors of lymph node metastasis in PNETs and their effects on prognosis through the inclusion of more impact factors.

6. Conclusion

In conclusion, this study was performed on PNETs patients who underwent surgical treatment in the SEER database. The research results confirmed that tumor located in pancreas head, distant metastasis, and poorly differentiated, undifferentiated, and unknown differentiated histology grades were three independent risk factors for lymph node metastasis. This suggested that regional lymphadenectomy should be carefully considered when choosing surgical treatment for these patients. In addition, lymph node metastasis is an independent prognostic factor of worse OS and DSS in patients with tumor located in the pancreas head. Lymph node metastasis was an independent prognostic factor of worse OS and DSS in patients without distant metastasis. However, lymph node metastasis was an independent prognostic factor for worse DSS in well differentiation and moderately differentiation groups. Prospective studies are required to more comprehensively understand the risk factors of lymph node metastasis and determine criteria in performing regional lymphadenectomy in patients with PNETs.

Data Availability

The data used to support the findings of the study “Risk factors of lymph node metastasis in patients with pancreatic neuroendocrine tumors (PNETs)” have been deposited in the SEER database. The method of obtaining data has been described in detail in the manuscript.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Authors’ Contributions

Study concept and design were done by Zhe Wang. Data acquisition, analysis, and interpretation were done by all authors. Drafting of the manuscript was done by Zhe Wang, Yupeng Zhang, and Yu Fang. Critical revision of the manuscript was done by all authors. Final approval of the manuscript was done by all authors.

Acknowledgments

This study is funded by the “Capital Medical University Clinical Medical High-Grade Discipline Construction” project (project number 1192070312).

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Copyright © 2020 Zhe Wang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


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