In this study, we showed that the PNI is associated with poor prognosis after surgical resection in patients with BTC, consistent with a previous report [7]. Tumor-related factors, including lymph node metastasis and tumor differentiation, were also found to be independent prognostic factors in multivariate analysis. Based on these findings, we developed a novel inflammation-based prognostic scoring system combining the PNI and pathological findings, which proved to be more effective than either marker alone.
A meta-analysis [16] showed that the PNI could be used as an independent prognostic marker for patients with BTC. Moreover, elevated neutrophil-to-lymphocyte and platelet-to-lymphocyte ratios may be unfavorable prognostic factors for clinical outcomes in patients with BTC [17].
The PNI, which is calculated using serum albumin concentration and total lymphocyte count, reflects the nutritional and immunological status of patients with cancer, and is a potential prognostic factor for survival. The mechanisms underlying the prognostic significance of the PNI in patients with BTC are discussed below.
Systemic inflammation has been shown to play an important role in cancer growth, invasion, and metastasis [18]. Total lymphocyte count is a component of the PNI. CD4 + and CD8 + T lymphocytes are major components of the immune microenvironment [19]. Tumor-infiltrating CD4 + and CD8 + T lymphocytes induce apoptosis and inhibit cancer cell proliferation [20]. Hence, lymphocytes play a critical role in cell-mediated antitumor immunity and immune surveillance [21]. Low lymphocyte counts lead to an insufficient immunological response in the tumor microenvironment, promoting cancer progression.
Malnutrition is common in patients with cancer [22], and has a negative impact on survival and recovery. Serum albumin concentration in the PNI reflects the nutritional status of patients with cancer. A low serum albumin concentration is associated with malnutrition and weight loss [23]. Hypoalbuminemia is not only a syndrome of poor nutritional status, but is also associated with a weakened host immune system [24]. Thus, a low serum albumin concentration usually predicts poor prognosis in patients with cancer. A low PNI may be predictive of an unfavorable prognosis in patients with BTC due to the aforementioned reason.
As discussed above, a low PNI may reflect systemic inflammation and progressive nutritional decline, resulting in poor survival. Perioperative nutritional support is recommended to improve the nutritional status of patients with hepatobiliary pancreatic carcinoma who have a high prevalence of malnutrition [25]. Preoperative immunonutrition has been reported to suppress the perioperative inflammatory response [26]. Further studies evaluating the relationship between immunonutrition and this inflammation-based prognostic score are required to improve the management of patients with BTC with a low PNI.
It is well known that clinicopathological characteristics, such as lymph node metastasis and tumor differentiation, significantly affect the prognosis of patients with cancer. Independent prognostic factors in this study included lymph node metastasis and tumor differentiation. Previous studies [27, 28] have shown that tumor differentiation is a predictor of survival after curative resection of BTC. In this study, patients with well-differentiated tumors had significantly longer survival times than those with other histologies. This was further confirmed by multivariate analysis. These findings suggest that tumor differentiation is a predictor of long-term survival. Patients with poorly differentiated tumors should be carefully monitored during postoperative follow-up to detect recurrence early.
Clinicopathological predictors have proven to be suboptimal for identifying high-risk patients. Recent evidence has underscored the discriminatory power of a combined prognostic index. Pinato et al. [29] proposed a new prognostic score for hepatocellular carcinoma based on a combination of the modified Glasgow prognostic score and the Cancer of the Liver Italian Program score. They reported that the predictive accuracy of the combined score was superior to that of the Cancer of the Liver Italian Program score alone. Lin et al. [30] combined the lymphocyte-to-monocyte ratio and pathological TNM stage to establish the inflammation-based pathological stage. They showed that the inflammation-based pathological stage was superior to either the pathological TNM stage or inflammation-based index alone. There are few established staging systems for BTC. In this study, we showed that the prognostic power of a combined scoring system may be more effective than the PNI alone. Our combined scoring system accurately predicted prognosis and can be applied as a novel prognostic indicator for patients with BTC.
The PNI was associated with several clinicopathological factors in this study. A low PNI was associated with lymph node metastasis and a longer operation time, suggesting that patients with a low PNI are at high risk of advanced disease.
This study has several limitations related to its single-center retrospective design and small sample size. The sample size limited the statistical power of multivariate and subgroup analyses. The study population was heterogeneous in terms of diagnosis and type of resection. The OS rates differed for each type of BTC (ICC, GBC, extrahepatic cholangiocarcinoma, etc.), although not statistically significant. Most patients underwent radical resection. However, in patients with early-stage GBC, less invasive resections, such as cholecystectomy and liver bed resection, were more commonly performed. Future prospective multicenter studies with larger sample sizes are needed to validate our findings.