Preoperative lymphocyte count as a prognostic factor in resected pancreatic ductal adenocarcinoma

Abstract

Background and aims. Recognized prognostic factors for resected pancreatic ductal adenocarcinoma (PDAC) include tumour size, differentiation, resection margin involvement and lymph node metastases. A further prognostic factor of less certain significance is lymphocyte count. The aim of this study was to investigate whether preoperative lymphocyte count is a prognostic indicator in patients with PDAC. Material and methods. Patients who had undergone a potentially curative pancreaticoduodenectomy (PD) for PDAC between 1998 and 2005 were analysed. Standard prognostic factors, preoperative lymphocyte count, preoperative neutrophil count and survival data were collected. Results. Of the 44 patients studied, univariate analysis identified predictors of a poor survival as lymph node status (node positive (+ve) 10.3 [5.4–20.9] months versus node negative (−ve) 14.2 [10.9–31.4] months; p=0.038), posterior resection margin invasion (margin +ve 7.0 [5.1–15.0] months versus margin −ve 13.1 [10.0–28.3] months; p=0.025) and lymphocyte count below the reference range (<1.5×10⁹/litre 8.8 [7.0–13.1] months versus ≥1.5×10⁹/litre 14.3 [7.0–28.3] months; p=0.029). Low preoperative lymphocyte count (p=0.027) and posterior margin invasion (p=0.023) retained significance on multivariate analysis. Preoperative neutrophil to lymphocyte ratio was not a significant prognostic factor. Conclusion. Preoperative lymphocyte count is a significant prognostic factor in patients with PDAC.

Introduction

Pancreatic ductal adenocarcinoma (PDAC) is a disease with a poor prognosis and a median survival of 12–18 months when resected with curative intent ¹,²,³,⁴,⁵,⁶,⁷,⁸,⁹,¹⁰,¹¹. However, there are few actual 5-year survivors, with even fewer patients truly cured of the disease ¹⁰. In a study of over 100,000 patients diagnosed with pancreatic cancer, only 9% were eligible for potentially curative resection ¹². The majority of pancreatic cancers are in the head of the gland, i.e. necessitating pancreaticoduodenectomy (PD). This is a major operative intervention normally associated with a high mortality and morbidity, although large series with no in-hospital or 30-day mortality have been reported from specialist centers ¹³.

Well-established prognostic factors include tumour size, differentiation, resection margin involvement and lymph node metastases ¹,³,⁸,⁹,¹⁰,¹¹,¹⁴,¹⁵. A further prognostic factor of less certain significance is lymphocyte count, which has previously been shown to be associated with shorter survival ¹⁶,¹⁷. Lymphocytopenia has been reported in various cancers, but is particularly marked in patients with PDAC ¹⁸,¹⁹,²⁰. It has been suggested that a low lymphocyte count indicates a state of immunosuppression, which is thought to be present at a systemic ²¹ and local level in patients with PDAC ²¹,²²,²³,²⁴,²⁵. In these studies, quantitative and functional deficiencies of lymphocytes were identified and it is therefore hypothesized that this may contribute to the poor prognosis of PDAC with a reduced host response against tumour cells.

The aim of this study was to investigate whether preoperative lymphocyte count is a prognostic indicator in patients with PDAC.

Methods

Patients who had undergone a potentially curative PD for pancreatic cancer between 1998 and 2005 were identified. Only those with PDAC confirmed on pathological examination were included in the analysis. Data were collected from a prospectively collected database and supplemented by retrospective case note review and cross-referenced against the laboratory computerized results system.

Standard histopathological prognostic factors including lymph node involvement, resection margin involvement, tumour size and differentiation were collected to ensure lymphocyte counts were independent of these. Demographic data including age at operation, sex, and survival (date of operation to date of death) were collected. In addition, lymphocyte and neutrophil counts on routine blood tests taken in the week prior to surgery were recorded. The median lymphocyte and neutrophil counts were calculated. Patients were grouped according to whether the lymphocyte count was above or below the lower limit of the normal reference range (1.5×10⁹/litre). Furthermore, the preoperative neutrophil to lymphocyte count ratio was calculated. Patients were grouped according to whether their neutrophil to lymphocyte ratio (NLR) was less than or greater than 5.

Statview version 5.0.1 software was used for statistical analysis. Continuous data are presented as median (interquartile range). Actual survival was assessed by the Kaplan-Meier method and comparisons were made using the log rank test. Multivariate analysis was performed to determine the significance of prognostic variables using the Cox proportional hazards method. A p-value of <0.05 was considered significant.

Results

Forty-four patients with a median age of 65 (59–71) years were analysed. The median survival was 11.7 (6.4–17.0) months. Potential prognostic factors are given in Table I. On univariate analysis, lymph node status (node positive (+ve) 10.3 [5.4–20.9] months versus node negative (−ve) 14.2 [10.9–31.4] months; p=0.038), posterior resection margin involvement (margin +ve 7.0 [5.1–15.0] months versus margin −ve 13.1 [10.0–28.3] months; p=0.025) and lymphocyte count (<1.5×10⁹/litre 8.8 [5.3–13.3] months versus ≥1.5×10⁹/litre 15.0 [10.0–28.3] months; p=0.0087) were shown to be predictors of a poor survival. Low lymphocyte count (p=0.027) and posterior margin invasion (p=0.023) remained significant on multivariate analysis (Figures 1 and 2). Tumour size, resection margin involvement (any margin), differentiation and preoperative NLR were found not to be significant prognostic factors.

Table I. Prognostic factors in patients with PDAC.

Variable		n	Median survival (IQR) (months)	p-value univariate analysis	p-value multivariate analysis
Lymph nodes involved	+ve	34	10.3 (5.4–20.9)	p=0.038	p=0.20
	−ve	10	14.2 (10.9–31.4)
Posterior resection margin	+ve	16	7.0 (5.1–15.0)	p=0.025	p=0.023
	−ve	28	13.1 (10.0–28.3)
Resection margin	+ve	21	8.8 (5.4–15.0)	p=0.10	–
	−ve	23	14.3 (9.9–28.3)
Tumour size ≤2 cm	≤2 cm	6	20.9 (19.9–31.4)	p=0.18	–
	>2 cm	38	10.3 (7.0–19.6)
Poorly differentiated	Yes	20	8.7 (5.1–12.7)	p=0.44	–
	No	24	14.8 (8.8–27.9)
Neutrophil to lymphocyte ratio ≥5	Yes	4	8.9 (5.3–13.3)	p=0.16	–
	No	40	10.5 (7.1–21.2)
Lymphocyte count <1.5×109/litre	Yes	20	8.8 (5.3–13.3)	p=0.0087	p=0.027
	No	24	15.0 (10.0–28.3)

Figure 1. .

Effect of posterior margin invasion on survival *univariate analysis.

Figure 2. .

Effect of lymphocyte count on survival *univariate analysis.

Discussion

Pancreatic cancer is a disease with a poor prognosis. Of the prognostic variables analysed, low preoperative lymphocyte count and posterior resection margin were found to be significant on multivariate analysis (Figures 1 and 2).

Although invasion of the posterior resection margin was identified as a significant prognostic factor, involvement of the resection margin (any margin) was not a significant prognostic variable (p=0.10). Residual tumour is often found at the posterior resection margin with complete resection sometimes difficult due to the immediate proximity of major vascular structures. Invasion specifically of the posterior resection margin has previously been identified to be associated with an adverse prognosis ⁵,⁶,¹⁴,²⁶.

Preoperative lymphocyte count less than the lower limit of the reference range (1.5×10⁹/litre) was also found to be a predictor of shorter survival on multivariate analysis (p=0.027). Preoperative lymphocyte count has previously been shown to be predictive of survival in patients with potentially resectable PDAC ¹⁶,¹⁷; however, the numbers of subjects in these studies were small. The current study consisted only of patients who underwent pancreaticoduodenectomy for PDAC (as confirmed by pathological analysis) representing a very select group, removing the potentially confounding variable of tumour type but confirming the previous findings.

Although lymphocyte count was a significant prognostic factor, the NLR was not. In the present study, patients were grouped according to whether their NLR was less than or greater then 5, as previous studies have shown that a preoperative NLR of >5 has a prognostic significance in patients undergoing resection of colorectal cancer and colorectal cancer liver metastases ²⁸,²⁹. In the present study, only 4 patients had a neutrophil to lymphocyte count >5, and therefore the results of the present study are difficult to interpret with respect to the prognostic value of the NLR. However, given that the majority of patients in this study had a normal neutrophil count, the observed lymphocytopenia of patients included in this study is less likely to be due to biliary sepsis, which would be associated with an increased neutrophil count and reduced lymphocyte count ²⁷.

The prognostic value of lymphocyte count in irresectable PDAC has not been reported in the litreature. However, leukocytosis has previously been shown to be associated with poor prognosis in patients with irresectable PDAC ³⁰. It was suggested that this may be explained by the significant morbidity and mortality associated with cholangitis with which a high white cell count would be expected.

Lymphocytopenia is present in many types of cancers and is thought to reflect a generalized state of depressed immune function ¹⁸. Depressed immune function may influence survival adversely due to reduced host response to the tumour cells. A study comparing patients with pancreatic, gastric and colorectal carcinoma found that patients with PDAC had more marked lymphocytopenia preoperatively and postoperatively ²⁰.

In patients with PDAC, increasing T-stage has been shown to correlate with decreasing CD3-, CD4- and CD8- lymphocyte counts ¹⁸. Furthermore, part of the host defence against PDAC is thought to involve local tumour infiltration with lymphocytes ²¹,²²,²³. It has been shown that tumour infiltration with a large number of CD4+ and CD8+ lymphocytes in PDAC is associated with improved prognosis ²².

Immunological tumour escape mechanisms involving lymphocytes have also been identified in PDAC, which may potentially adversely influence survival. The Fas system, which comprises the Fas receptor and its ligand, Fas ligand (FasL), is a central mediator of apoptosis under physiological and pathological conditions ³¹. Abnormal expression of functional FasL has been shown to occur in PDAC cells and is thought to induce apoptosis of tumour infiltrating lymphocytes which have high expression of the Fas receptor ²⁴,²⁵. Impairment of T cell function is also thought to occur in PDAC due to high circulating levels of the inhibitory cytokines interleukin-10 and transforming growth factor-β1/2 with inactivation of these cells being reflected by loss of the CD3κ chain ²¹. In the majority of PDAC specimens, lymphocytes are “trapped” in fibrous peritumoral tissue and prevented from infiltrating the cancer, a further possible tumour escape mechanism ²¹.

Another simple blood test, which has been identified to have prognostic significance in patients with PDAC, is C-reactive protein (CRP) ³²,³³,³⁴,³⁵,³⁶,³⁷. This has been shown to correlate inversely with survival and was used in these studies as an index measurement of the systemic inflammatory response which is thought to exist in PDAC patients. A raised CRP level has also been shown to be related to the degree of cancer cachexia ³²,³³,³⁸. Furthermore, encouraging results have been achieved using combined adjuvant chemoradiotherapy and immunotherapy with a reported 5-year survival of 55% ³⁹. Taken together, these findings suggest that there may be an immunological basis to this disease.

The well-established prognostic variables in resected PDAC are pathological features, but few discriminating preoperative variables have been identified as having prognostic significance in patients with potentially resectable PDAC. The results of this study suggest that lymphocyte count may be useful in determining prognosis in patients with PDAC. This study also adds to the body of evidence suggesting that immunological mechanisms may contribute to the poor prognosis of PDAC. If the results of this study are borne out in a larger study, preoperative lymphocyte count could potentially be included in a prognostic nomogram for PDAC similar to that previously constructed by Brennan et al. ¹¹.