This is the first study of serum uPA levels in HCC patients. We found that HCC patients with high pre-operative uPA (serum uPA ≥1 ng/ml) exhibited lower OS rates after curative hepatic resection surgery. Furthermore, the combination of serum uPA and AFP could also be important in determining postoperative outcomes in response to the surgical procedure. These results may not only assist surgeons in predicting HCC patient survival but remind clinical physicians to perform timely adjuvant treatments to improve the prognosis of patients with high preoperative serum levels of uPA.
Many studies have investigated the clinical impact of the expression of members of the uPA system and their correlation with prognosis in a wide variety of cancers []. However, only one study has been conducted for HCC patients so far []. In 2000, Zheng et al. found that increasing uPA protein levels in HCC tissue was associated with increased invasion and metastasis in 22 HCC patients []. Nevertheless, commercially available tests are not extensively used because they require a great amount of fresh-frozen tissue or formalin-fixed paraffin-embedded samples.
Aside from detection in the tissue, uPA can be shed by stromal cells or tumor cells into the bloodstream and measured in serum or plasma. Many studies have indicated that serum uPA can be used to predict the outcomes of cancer patients, although conflicting results have been reported, and none of the studies have been conducted with HCC patients [[14-18]]. In the current study, we found that elevated serum uPA levels were related to poorer OS in HCC patients undergoing resection, regardless of whether it is evaluated dichotomously (p = 0.002) or continuously (p = 0.005).
The multivariate Cox regression analysis indicated that elevated serum uPA was an independent prognostic factor for OS in HCC patients (p = 0.006). These results are consistent with those obtained with other cancers, including prostate cancer [] and gastrointestinal cancer []. Recently, Wei et al. showed that SPINK13, a suppressor of the proliferation of HCC cells, directly interacted with uPA, inhibited the cleavage of MMP9 by uPA, and achieved antitumor activity on HCC cells []. Future clinical studies are required to verify whether high serum uPA might be useful for identifying HCC patients who are most likely to benefit from SPINK13, and trials for adjuvant treatment after resection are being planned.
AFP is the most useful and cost-effect serum biomarker to evaluate the prognosis of AFP-positive HCC patients in clinical practice. However, in the present study, AFP was not an independent predictive factor for OS. To consider the impact of serum AFP on OS as much as possible, serum uPA and AFP were considered together. We found that the OS rates were significantly poorer in those with high uPA and AFP than in other groups. This demonstrated that the combination of serum uPA and AFP had more capacity to predict patients’ outcomes. Importantly, in subgroups with low or high AFP levels, serum uPA still had the ability to discriminate HCC patients undergoing curative resection with good prognoses from those with poor OS. More studies are required to validate the clinical role in different types of management, such as radiofrequency ablation (RFA) or transcatheter arterial chemoembolization (TACE).
We found that serum uPA was significantly elevated in HCC patients with liver cirrhosis, hypoalbuminemia, and thrombocytopenia, which provides additional evidence that elevated serum uPA may play a role in the prediction of liver fibrosis severity. Hepatic fibrosis is characterized by the progressive deposition of extracellular matrix (ECM) in patients with chronic liver injury. Hepatic stellate cells (HSCs) are the major source of ECM in the liver. They are also the primary cellular mediator of hepatic fibrosis through their transdifferentiation, or activation from a vitamin A-storing cell to a contractile, matrix-producing myofibroblast in response to liver injury and inflammation [[22, 23]]. TGF-β triggers the uPA pathway, which activates quiescent HSCs and causes ECM deposition []. Hence, uPA is considered to be involved in liver fibrosis through the regulation of HSCs.
Serum uPA was associated with the fibrosis stage in this study (p<0.001, Figure S1). Recently, Liu et al. indicated that the stage of hepatic fibrosis in HCV-infected patients could be accurately assessed using BioFibroScore, a novel serological panel including uPA, matrix metalloproteinase-9, and beta-2 microglobulin []. This prompted us to combine other serum fibrotic markers to investigate the prognostic value of serum uPA in the prediction of the fibrotic stage in HCC patients in future studies.
Aside from uPA, our univariate analyses showed that the AFP level, tumor size, vascular invasion, and pathology stage were also significant prognostic factors associated with the OS of HCC patients undergoing curative resection. However, the multivariate analysis demonstrated that only vascular invasion and the pathology stage were independent prognostic factors for OS. This is consistent with the results of previous studies in which tumor-related factors (vascular invasion and histological stage) determined the outcomes of HCC patients undergoing resection [].
Our study had three main limitations. First, only HCC patients undergoing resection were enrolled. Second, this is a retrospective study, and some patients were lost to follow-up after operation. Third, all patients in this cohort were treated at a tertiary medical center, which means that referral bias could not be completely avoided. These data should be validated externally in other regions of the world. Finally, more information from patients with chronic liver disease without HCC, as well as healthy individuals, should be collected for further investigation together, which will be included in our future work.
In summary, we have presented for the first time that the serum uPA level is a clinically relevant biomarker in HCC patients receiving curative resection, with higher expression of uPA being associated with higher mortality. This also highlights the potential utility of uPA as a therapeutic target for improved treatment strategies. A recent study on a uPA inhibitor, SPINK13, provided exciting and promising evidence of an antitumor effect in a mouse model of HCC. Thus, future research should aim at clarifying whether elevated serum uPA may be useful for identifying patients that are likely to derive clinical benefit from a targeted strategy.