https://doi.org/10.5812/ijcm.104861

Predictive Value of Lymph Node Ratio in Patients with Pancreatic Cancer Treated with Pancreatoduodenectomy

authors:

avatar Mahdi Attarian 1 , avatar Mohsen Aliakbarian ORCID 2 , * , avatar Ali Taghizadeh kermani ORCID 2 , avatar Fahimeh Attarian 3 , avatar Sakineh Amouian 4 , avatar Mona Najaf Najafi ORCID 5

Mashhad University of Medical Sciences, Mashhad, Iran
Surgical Oncology Research Center, Imam Reza Hospital, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran
School of Public Health, Iran University of Medical Sciences, Tehran, Iran
Departement of Pathology, Imam Reza Hospital, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran
Imam Reza Clinical Research Units, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran
International Journal of Cancer Management: Vol.14, issue 3; e104861
published online: March 30, 2021
article type: Research Article
received: May 12, 2020
revised: December 6, 2020
accepted: December 7, 2020

how to cite: Attarian M, Aliakbarian M, Taghizadeh kermani A, Attarian F , Amouian S , et al. Predictive Value of Lymph Node Ratio in Patients with Pancreatic Cancer Treated with Pancreatoduodenectomy. Int J Cancer Manag. 2021;14(3):e104861. https://doi.org/10.5812/ijcm.104861.

Abstract

Background:

Recently, the predictive value of lymph node ratio (LNR, the ratio of metastatic lymph nodes to total examined lymph nodes) has been evaluated in patients with gastrointestinal malignancies, including pancreatic cancer. However, there is not enough evidence about the prognostic value of this factor.

Objectives:

We aimed at determining the value of LNR in predicting the survival of patients who have undergone the Whipple procedure.

Methods:

This cohort study was performed on 96 patients with pancreatic cancer undergoing the Whipple procedure during 2014 - 2019. Demographic, clinical, and pathological data of the patients were extracted from their records and patients' survival status was determined through follow-up. LNR and its effect on survival was calculated using the Cox model.

Results:

Of the 96 eligible patients, 51 (53.13%) were men. The mean age of the patients was 57.1 ± 14.1 (range: 19 - 82) years. The median total lymph nodes examined was 7 (range: 1 - 27), and no metastatic lymph nodes were found in 57 (59.37%) patients. The median involved lymph nodes and LNR were 2 and 0.17, respectively. Patients with LNR > 0.20 had the lowest 1 and 3-year survival rates. Age (P = 0.04), surgical radial margin (P = 0.001), lymph node status (N0, N1) (P = 0.01), and LNR (P = 0.01) were the most important prognostic factors for survival.

Conclusions:

LNR is a valuable indicator that can be used in patients with lymph node involvement as a prognostic factor for poor survival after the Whipple procedure. The lowest 1, 3, and 5-year survival rates were seen in patients with LNR > 0.20.

1. Background

Pancreatic cancer is one of the deadliest malignancies and the seventh leading cause of cancer-related death worldwide (1) with a mortality rate of 97.7% (2). The 5-year survival rate is estimated to be 10% in all patients and 32% in patients without distant metastasis (3). Currently, surgery followed by adjuvant therapy is the most promising treatment, although surgery can only be performed in 20 to 30% of the patients (3-5) with only 10 to 20% chance of long-term survival (6, 7). Neoadjuvant treatments or postoperative adjuvant therapies are also associated with increased patient survival (8-10). Moreover, the experience of the surgical team and the age of the patients can also influence the mortality rate and patient survival (11, 12). Some pathological factors such as tumor size, lymph node status, surgical margin, and tumor grade are also considered as prognostic factors (8). Discovering prognostic factors that affect survival rate in patients with pancreatic adenocarcinoma can allow the physician to accurately select subsequent treatments and thus increase survival rates. One of the recently considered factors is lymph node ratio (LNR) which is the ratio of metastatic lymph nodes to total lymph nodes examined.

One of the main prognostic factors in determining survival rate is the presence or absence of involved lymph nodes (LNs), which may be affected by the total number of resected LNs. Although the minimum accepted number of total resected LNs is controversial but it depends on the experience and skill of the surgeon, and the precise pathology examination (13-16).

2. Objectives

Most studies consider long-term survival after surgery in the absence of metastatic lymph nodes (13, 14, 17). Although lymph node involvement is a common condition in most patients undergoing surgery (14, 18), an increase in the number of metastatic lymph nodes can be a sign of poor survival (17). Ultimately, LNR evaluation has been suggested for predicting postoperative survival rate (19-23). There is no certainty about the value of this ratio and conflicting results have been reported (15, 17). Therefore, this study aimed at evaluating the value of LNR for predicting a 5-year survival rate in patients with pancreatic cancer undergoing the Whipple procedure.

3. Methods

This cohort study was performed on 96 patients with pancreatic cancer undergoing the Whipple procedure at Imam Reza Hospital, Mashhad, northeast Iran, during 2014 - 2019. Patients with pancreatic malignancy whose cancer could be resected based on clinical and radiological criteria were included. Patients with the unresectable or borderline resectable disease, presence of distant visceral metastasis, a pathological diagnosis other than adenocarcinoma, and history of receiving neoadjuvant treatments including radiotherapy or chemotherapy were excluded. All patients signed a written informed consent form before surgery. The ethics committee of Mashhad University of medical sciences approved the study. A pylorus-preserving Whipple procedure was performed for all patients and lymphadenectomy including LN stations no. 5, 6, 8a, 12b1, 12b2, 12c, 13a, 13b, 14a, 14b, 17a, and 17b.

Demographic and pathological information including age, sex, tumor differentiation, surgical margin, the total number of lymph nodes examined, and number of lymph nodes in patients with metastasis were recorded. The tumor stage was then determined for each patient based on TNM classification. According to the pathological report of the initial biopsy, the tumor differentiation was as follows: (1) differentiated G1, (2) moderately differentiated G2, and (3) poorly differentiated G3. The condition of the marginal radial tumor (positive/negative) was also defined. The LNR was determined based on the ratio of the number of lymph nodes involved (N1) to the total number of lymph nodes examined, and was divided into 3 levels based on survival sensitivity at different levels of the ratio. In this prospective study, patients were followed up by active phone calls. This study was approved by the Ethics Committee of Mashhad University of Medical Sciences.

All analyses in this study were performed using STATA software, version 12 (STATA Corporation, College Station, TX, USA, 2009). Firstly, all data from the observations were described by type. Descriptive statistics such as frequency (percentage), median, mean and standard deviation were used as appropriate. Survival was calculated using the Kaplan Meier method. Then the relationship between each demographic and pathological factor and survival was evaluated. To determine the accepted cut-off ratio of the lymph nodes, the survival chart was plotted for each of the possible cut-off points, and finally, in the multivariate model, the predictive value of the variables was reported by controlling other variables. P < 0.05 was considered as statistically significant.

4. Results

Of the 96 patients eligible for the study, 51 (53.13%) were men. The mean age of patients was 57.1 ± 14.1 (range: 19 - 82) years and 25 (26.04%) patients were over 65 years of age. The overall 1, 3 and 5-year survival rates for all the patients were 71, 53, and 34%, respectively. The median survival rate was 14.11 months, ranging from 18 days to 60 months.

The median total lymph nodes evaluated in the patients was 7 (range: 1 - 27), and no metastatic lymph nodes were found in 57 (59.37%) patients. In 39 patients with metastatic lymph nodes, 1 to 12 (median: 2) lymph nodes were involved. The median LNR was 0.17 in patients with metastatic lymph nodes. Radial tumor margin was negative in 80 (83.33%) patients and the disease stage was 2 or 3 in 52% of the patients. Moreover, tumor differentiation was moderate or poor in 72 (75%) patients (Table 1). The value of each of the independent clinicopathological factors was evaluated to determine its significance as a prognostic factor and survival was compared through the log-rank test (Table 2).

Table 1.

Characteristics of Patients under Study (N = 96) a

VariablesValues
Sex
Female45 (46.88)
Male51 (53.13)
Age (y)
≤ 6571 (73.95)
> 6525 (26.04)
Radial margin
R080 (83.33)
R116 (16.67)
Adjuvant chemotherapy
Yes57 (59.38)
No39 (40.63)
Tumor differentiation
Well (G1)24 (25.56)
Moderate (G2)66 (68.75)
Poor (G3)6 (6.25)
Tumor stage
T08 (8.16)
T112 (12.50)
T255 (57.29)
T32 (21.88)
Node stage
N057 (59.37)
N139 (40.62)
Disease stage
08 (8.33)
IA, IB38 (39.58)
IIA, IIB, III50 (52.08)
Tumor size (cm), median (min, max)3 (1, 11)
Total examined lymph nodes, mean (min, max)8.11 (1, 27)
Metastatic lymph nodes, mean (min, max)1.18 (1, 12)

a Values are expressed as No. (%) unless otherwise indicated.

Table 2.

Distribution Some of Prognostic Factors Stratified by Lymph Node Ratio

Variable (N)LNR0LNR1LNR2P-Value
Tumor size (cm)0.75
≤ 21383
> 2391914
Gender0.660
Female26109
Male30147
Radial margin< 0.001
R052208
R1448
Age (y)0.10
≤ 65441413
> 6513102
Tumor stage0.161
0800
IA, IB3800
IIA, IIB, III102416

Abbreviations: N, number; LNR, lymph node ratio.

There was no association between sex, tumor size, tumor differentiation rate, disease stage, and the total number of metastatic lymph nodes and overall survival rate; although age (P = 0.04), surgical radial margin (P = 0.001), lymph node status (N0, N1) (P = 0.01) and LNR (P = 0.01) were the most important prognostic factors for survival in the patients.

Considering a cut-off point of 0.17, the overall survival of patients was significantly differed when they were divided into 3 groups based on LNR levels (LNR = 0, 0 < LNR ≤ 0.17, and LNR > 0.17) (P = 0.01) (Figure 1). However, this difference was also significant when the cut-off was 0.20 (P = 0.03) (Figure 2). By comparing the figures, we found that the best cut-off for the evaluated data could be 0.20. Ultimately, the results of multivariate analysis showed that in this sample only age of over 65 years was the most important prognostic factor for poor survival in patients (HR = 2.30, CI = 95%, 1.10, 4.78), while LNR more than 0.20 (HR = 2.62, P = 0.05) and positive radial margin (HR = 2.10, P = 0.05) can also predict poor patient survival.

The overall survival curves stratified by LNR considering a cut-off point of 0.17 (LNR: lymph node ratio).
The overall survival curves stratified by LNR considering a cut-off point of 0.17 (LNR: lymph node ratio).
Figure 1.

The overall survival curves stratified by LNR considering a cut-off point of 0.17 (LNR: lymph node ratio).

The overall survival curves stratified by LNR (cut-off point = 0.2), while LNR0, 1, 2 represents survival rate in patients with LNR 0, ≤ 0.2 and > 0.2, respectively.
The overall survival curves stratified by LNR (cut-off point = 0.2), while LNR0, 1, 2 represents survival rate in patients with LNR 0, ≤ 0.2 and > 0.2, respectively.
Figure 2.

The overall survival curves stratified by LNR (cut-off point = 0.2), while LNR0, 1, 2 represents survival rate in patients with LNR 0, ≤ 0.2 and > 0.2, respectively.

5. Discussion

In this study, which lasted 5 years, 96 patients with pancreatic cancer who underwent the Whipple procedure were followed up to identify prognostic factors affecting their survival rate. Lymph node involvement and positive margin were prognostic factors for poor survival in patients with pancreatic cancer in this study which is in line with previous studies (14, 21, 22).

Recent evidence has shown the value of the number of metastatic LNs and LNR to predict postoperative survival (23). Some studies have found a significant relationship between the number of metastatic lymph nodes and survival rate (17). However, the number of lymph nodes involved is more dependent on the number of lymph nodes resected and examined so that this number could increase as the number of resected and examined lymph nodes increase (15, 24, 25). In some studies, the value of the lymph nodes involved is accepted as a weak predictor of survival only when the total number of lymph nodes examined is more than 10; and some studies have stated a median of 7 to 17 to be suitable as the total number of examined lymph nodes (13, 19). In contrast, some studies did not show any significant prognostic value for the number of examined lymph nodes in patients (26, 27).

Using lymph node ratio can control these challenges and provide a better indicator of the total number of lymph nodes and lymph nodes involved (13). Therefore, our focus has been on determining the predictive value of lymph node ratio for patient survival. This study showed LNR can be used as a prognostic factor for survival in patients undergoing Whipple procedure, which is consistent with previous studies (18, 19, 21, 23, 28, 29). LNR was first proposed in 2004 as a predictor for survival in patients with pancreatic cancer in a study evaluating the survival rate in 128 patients undergoing pancreatectomy (13). Subsequently, in a second study on data obtained from 4005 patients with pancreatic cancer (SEER database from 1998 to 2003), LNR was reported as a prognostic factor for survival in patients (30). If this ratio is zero in patients, the highest survival rate of 1, 3, and 5 years would be expected (15, 31). Subsequent reports suggested that if this ratio was greater than zero, the mortality rate may even follow a linear pattern and increase with the increased LNR (14). However, researchers tend to categorize this ratio and determine a cut-off for it (19).

In the present study, the greatest difference in survival rate was seen at a cut-off point of 0.20, so that patients with 0 < LNR ≤ 0.2 had a higher 1, 3, and 5-year survival rate compared with those with an LNR > 0.2 and the lowest 1-year (62%) and three-year (25%) survival rate was seen in patients with LNR > 0.2 (although in this cohort no patient had an LNR greater than 0.20 and followed for up to 5 years). In general, determining the appropriate cut-off point is challenging when using any continuous quantitative ratio, because the cut-off must be able to separate statistically significant levels. In some previous studies, the median of this ratio was used as the cut-off point (25), but in the present study, we considered the median and the cut-off most studies reported as suitable (21).

We evaluated the survival rate of patients at the 2 cut-off points of 0.20 and 0.17. House et al. evaluated data from 696 patients with pancreatic cancer and found the highest difference in survival rate when a cut-off point of 0.18 was considered and patients with LNR > 0.18 had the weakest survival rate (28). Berger et al. also selected a cut-point of 0.15 in evaluating the data of 124 patients (13). In general, researchers have selected cut-off points of 0.15 to 0.2. Many previous studies on patients with gastrointestinal malignancies including pancreatic cancer have reported a significant association between lymph node status and patient survival, and lymph node involvement has been suggested as a prognostic factor for poor survival (13, 14, 17, 19, 29, 31). The results of this study also showed that lymph node involvement could be a prognostic factor for pancreatic cancer in patients with metastatic lymph node (N1), in whom lower 1, 3, and 5-year survival rates were seen compared to patients without lymph node involvement (N0).

The major limitation of the study was the sample size. Although the cut-off point of 0.2 would predict patient survival, it should be taken into consideration that 60 patients were N0 and few patients (16 cases) had LNR ≥ 0.2. As well, the small sample size in each different stage may affect the survival distinction between the groups and so we did not find any significant relationship between cancer stage and survival rate. Therefore, the results of this study should be confirmed by subsequent larger or multicenter studies. Another limitation was few examined lymph nodes in some cases which is related to the suboptimal examination of lymph nodes.

5.1. Conclusion

LNR is a valuable indicator that can be used in patients with lymph node involvement as a prognostic factor for poor survival after the Whipple procedure. The lowest 1, 3, and 5-year survival rates were seen in patients with LNR > 0.20.

Acknowledgements

References

  • 1.

    Siegel RL, Miller KD, Jemal A. Cancer statistics, 2018. CA Cancer J Clin. 2018;68(1):7-30. [PubMed ID: 29313949]. https://doi.org/10.3322/caac.21442.

  • 2.

    Yeo CJ, Sohn TA, Cameron JL, Hruban RH, Lillemoe KD, Pitt HA. Periampullary adenocarcinoma: Analysis of 5-year survivors. Ann Surg. 1998;227(6):821-31. [PubMed ID: 9637545]. [PubMed Central ID: PMC1191384]. https://doi.org/10.1097/00000658-199806000-00005.

  • 3.

    Kawarada Y, Yokoi H, Isaji S, Naganuma T, Tabata M, Machishi H, et al. Modified standard pancreaticoduodenectomy for the treatment of pancreatic head cancer. Digestion. 1999;60(Suppl 1):120-5. [PubMed ID: 10026445]. https://doi.org/10.1159/000051467.

  • 4.

    Birkmeyer JD, Sun Y, Wong SL, Stukel TA. Hospital volume and late survival after cancer surgery. Ann Surg. 2007;245(5):777-83. [PubMed ID: 17457171]. [PubMed Central ID: PMC1877074]. https://doi.org/10.1097/01.sla.0000252402.33814.dd.

  • 5.

    Fong Y, Gonen M, Rubin D, Radzyner M, Brennan MF. Long-term survival is superior after resection for cancer in high-volume centers. Ann Surg. 2005;242(4):540-7. [PubMed ID: 16192814]. [PubMed Central ID: PMC1402350]. https://doi.org/10.1097/01.sla.0000184190.20289.4b.

  • 6.

    Luo J, Xiao L, Wu C, Zheng Y, Zhao N. The incidence and survival rate of population-based pancreatic cancer patients: Shanghai cancer registry 2004-2009. PLoS One. 2013;8(10). e76052. [PubMed ID: 24130758]. [PubMed Central ID: PMC3794034]. https://doi.org/10.1371/journal.pone.0076052.

  • 7.

    Stewart BW, Wild CP. World cancer report 2014. Lyon, France: The International Agency for Research on Cancer; 2014.

  • 8.

    Yamamoto Y, Shimada K, Takeuchi Y, Sofue K, Shibamoto K, Nara S, et al. Assessment of the interface between retroperitoneal fat infiltration of pancreatic ductal carcinoma and the major artery by multidetector-row computed tomography: Surgical outcomes and correlation with histopathological extension. World J Surg. 2012;36(9):2192-201. [PubMed ID: 22562451]. https://doi.org/10.1007/s00268-012-1618-9.

  • 9.

    Rodriguez Santiago JM, Munoz E, Marti M, Quintana S, Veloso E, Marco C. Metastatic lymph node ratio as a prognostic factor in gastric cancer. Eur J Surg Oncol. 2005;31(1):59-66. [PubMed ID: 15642427]. https://doi.org/10.1016/j.ejso.2004.09.013.

  • 10.

    John BJ, Naik P, Ironside A, Davidson BR, Fusai G, Gillmore R, et al. Redefining the R1 resection for pancreatic ductal adenocarcinoma: Tumour lymph nodal burden and lymph node ratio are the only prognostic factors associated with survival. HPB (Oxford). 2013;15(9):674-80. [PubMed ID: 23458477]. [PubMed Central ID: PMC3948534]. https://doi.org/10.1111/hpb.12019.

  • 11.

    Ghaneh P, Kleeff J, Halloran CM, Raraty M, Jackson R, Melling J, et al. The impact of positive resection margins on survival and recurrence following resection and adjuvant chemotherapy for pancreatic ductal adenocarcinoma. Ann Surg. 2019;269(3):520-9. [PubMed ID: 29068800]. https://doi.org/10.1097/SLA.0000000000002557.

  • 12.

    Elshaer M, Gravante G, Kosmin M, Riaz A, Al-Bahrani A. A systematic review of the prognostic value of lymph node ratio, number of positive nodes and total nodes examined in pancreatic ductal adenocarcinoma. Ann R Coll Surg Engl. 2017;99(2):101-6. [PubMed ID: 27869496]. [PubMed Central ID: PMC5392844]. https://doi.org/10.1308/rcsann.2016.0340.

  • 13.

    Berger AC, Watson JC, Ross EA, Hoffman JP. The metastatic/examined lymph node ratio is an important prognostic factor after pancreaticoduodenectomy for pancreatic adenocarcinoma. Am Surg. 2004;70(3):235-40. [PubMed ID: 15055847].

  • 14.

    Sierzega M, Popiela T, Kulig J, Nowak K. The ratio of metastatic/resected lymph nodes is an independent prognostic factor in patients with node-positive pancreatic head cancer. Pancreas. 2006;33(3):240-5. [PubMed ID: 17003644]. https://doi.org/10.1097/01.mpa.0000235306.96486.2a.

  • 15.

    Slidell MB, Chang DC, Cameron JL, Wolfgang C, Herman JM, Schulick RD, et al. Impact of total lymph node count and lymph node ratio on staging and survival after pancreatectomy for pancreatic adenocarcinoma: A large, population-based analysis. Ann Surg Oncol. 2008;15(1):165-74. [PubMed ID: 17896141]. https://doi.org/10.1245/s10434-007-9587-1.

  • 16.

    Williams JL, Nguyen AH, Rochefort M, Muthusamy VR, Wainberg ZA, Dawson DW, et al. Pancreatic cancer patients with lymph node involvement by direct tumor extension have similar survival to those with node-negative disease. J Surg Oncol. 2015;112(4):396-402. [PubMed ID: 26303811]. https://doi.org/10.1002/jso.24011.

  • 17.

    Morales-Oyarvide V, Rubinson DA, Dunne RF, Kozak MM, Bui JL, Yuan C, et al. Lymph node metastases in resected pancreatic ductal adenocarcinoma: Predictors of disease recurrence and survival. Br J Cancer. 2017;117(12):1874-82. [PubMed ID: 28982112]. [PubMed Central ID: PMC5729468]. https://doi.org/10.1038/bjc.2017.349.

  • 18.

    Kang MJ, Jang JY, Chang YR, Kwon W, Jung W, Kim SW. Revisiting the concept of lymph node metastases of pancreatic head cancer: Number of metastatic lymph nodes and lymph node ratio according to N stage. Ann Surg Oncol. 2014;21(5):1545-51. [PubMed ID: 24419758]. https://doi.org/10.1245/s10434-013-3473-9.

  • 19.

    International Union Against Cancer (UICC). TNM classification of malignant tumours (UICC). 6th ed. New York, USA: Wiley-Liss; 2002. p. 93-6.

  • 20.

    He C, Zhang Y, Cai Z, Lin X, Li S. Overall survival and cancer-specific survival in patients with surgically resected pancreatic head adenocarcinoma: A competing risk nomogram analysis. J Cancer. 2018;9(17):3156-67. [PubMed ID: 30210639]. [PubMed Central ID: PMC6134825]. https://doi.org/10.7150/jca.25494.

  • 21.

    Pawlik TM, Gleisner AL, Cameron JL, Winter JM, Assumpcao L, Lillemoe KD, et al. Prognostic relevance of lymph node ratio following pancreaticoduodenectomy for pancreatic cancer. Surgery. 2007;141(5):610-8. [PubMed ID: 17462460]. https://doi.org/10.1016/j.surg.2006.12.013.

  • 22.

    Riediger H, Keck T, Wellner U, zur Hausen A, Adam U, Hopt UT, et al. The lymph node ratio is the strongest prognostic factor after resection of pancreatic cancer. J Gastrointest Surg. 2009;13(7):1337-44. [PubMed ID: 19418101]. https://doi.org/10.1007/s11605-009-0919-2.

  • 23.

    Cho DH, Bae SY, You JY, Kim HK, Chang YW, Choi YJ, et al. Lymph node ratio as an alternative to pN staging for predicting prognosis after neoadjuvant chemotherapy in breast cancer. Kaohsiung J Med Sci. 2018;34(6):341-7. [PubMed ID: 29747778]. https://doi.org/10.1016/j.kjms.2017.12.015.

  • 24.

    Tol JA, Brosens LA, van Dieren S, van Gulik TM, Busch OR, Besselink MG, et al. Impact of lymph node ratio on survival in patients with pancreatic and periampullary cancer. Br J Surg. 2015;102(3):237-45. [PubMed ID: 25529117]. https://doi.org/10.1002/bjs.9709.

  • 25.

    Yamamoto Y, Ikoma H, Morimura R, Konishi H, Murayama Y, Komatsu S, et al. The clinical impact of the lymph node ratio as a prognostic factor after resection of pancreatic cancer. Anticancer Res. 2014;34(5):2389-94. [PubMed ID: 24778048].

  • 26.

    Pu N, Li J, Xu Y, Lee W, Fang Y, Han X, et al. Comparison of prognostic prediction between nomogram based on lymph node ratio and AJCC 8th staging system for patients with resected pancreatic head carcinoma: A SEER analysis. Cancer Manag Res. 2018;10:227-38. [PubMed ID: 29440932]. [PubMed Central ID: PMC5804271]. https://doi.org/10.2147/CMAR.S157940.

  • 27.

    Roland CL, Katz MH, Gonzalez GM, Pisters PW, Vauthey JN, Wolff RA, et al. A high positive lymph node ratio is associated with distant recurrence after surgical resection of ampullary carcinoma. J Gastrointest Surg. 2012;16(11):2056-63. [PubMed ID: 22914983]. [PubMed Central ID: PMC5131719]. https://doi.org/10.1007/s11605-012-2015-2.

  • 28.

    House MG, Gonen M, Jarnagin WR, D'Angelica M, DeMatteo RP, Fong Y, et al. Prognostic significance of pathologic nodal status in patients with resected pancreatic cancer. J Gastrointest Surg. 2007;11(11):1549-55. [PubMed ID: 17786531]. https://doi.org/10.1007/s11605-007-0243-7.

  • 29.

    Schwarz RE, Smith DD. Extent of lymph node retrieval and pancreatic cancer survival: Information from a large US population database. Ann Surg Oncol. 2006;13(9):1189-200. [PubMed ID: 16955385]. https://doi.org/10.1245/s10434-006-9016-x.

  • 30.

    Hellan M, Sun CL, Artinyan A, Mojica-Manosa P, Bhatia S, Ellenhorn JD, et al. The impact of lymph node number on survival in patients with lymph node-negative pancreatic cancer. Pancreas. 2008;37(1):19-24. [PubMed ID: 18580439]. https://doi.org/10.1097/MPA.0b013e31816074c9.

  • 31.

    Ashfaq A, Pockaj BA, Gray RJ, Halfdanarson TR, Wasif N. Nodal counts and lymph node ratio impact survival after distal pancreatectomy for pancreatic adenocarcinoma. J Gastrointest Surg. 2014;18(11):1929-35. [PubMed ID: 24916590]. https://doi.org/10.1007/s11605-014-2566-5.