Primary liver cancer is the third leading cause of cancer-related deaths worldwide with more than 900,000 new cases annually (1). Hepatocellular carcinoma (HCC) is the major pathologic category of primary liver cancer (PLC) and accounts for ~90% of all pathological types. Although treatments for HCC have become increasingly diversified with the development of targeted therapy and immunotherapy (2), the prognosis remains poor (3). Hepatectomy and liver transplantation are the preferred therapies for HCC, according to the international guidelines. However, <30% of the patients receive surgical treatment. The study of Llovet et al. reported that the 5-year recurrence and metastasis rates were 40–70% after surgery (4). The 5-year recurrence rate after surgery is as high as 80% for tumors larger than 5 cm and 40–50% for tumors smaller than 5 cm (5). Early recurrence is a key factor affecting the overall survival (OS) in patients with HCC. Therefore, screening for early metastasis and predictors of recurrence is important.

Early recurrence is closely related to aggressive tumor cell growth. Microvascular invasion (MVI) is defined as the presence of tumor cells in the portal veins, large capsule vessels, or vascular spaces lined by endothelial cells (6), which can only be confirmed by postoperative histological examination. MVI can lead to the spread of tumor cells within the liver or distant metastasis. MVI is reportedly a negative factor that results in decreased long-term survival and early recurrence (7). The occurrence rate of MVI in patients with HCC ranges from 15 to 57% (8). For patients with HCC smaller than 5 cm, the disease-free survival (DFS) and OS rates are worse in patients with a high risk of MVI than in those with a low risk after radiofrequency ablation treatment (9). Different surgical resection methods and surgical margins also affect the prognosis of patients with HCC and MVI. Patients with surgical margins ≥1 cm have a lower postoperative recurrence rate and better long-term prognosis than those with a surgical margin <1 cm (10). According to a study by Ueno et al., anatomical segmentation is currently recommended as the standard surgical procedure for patients with HCC and MVI (11). However, the pathological detection rate of MVI in HCC and the impact on patient survival was depending on the tissue sampling protocol (12). The seven-point sampling protocol may not satisfy the detection of all the existing MVI. Therefore, precise identification of MVI is beneficial in choosing more suitable therapeutic decisions.

In our study, the clinicopathological data of patients with HCC with MVI were retrospectively analyzed. We explored the effect of MVI on the prognosis and identified the risk factors associated with MVI to provide clues identifying the HCC with a high risk of recurrence.

In HCC, MVI is a key risk factor for early recurrence after surgical resection (14). Our study found that the presence of MVI in HCC suggested a poor prognosis. Both DFS and OS times in MVI+ patients were worse than those in MVI– patients. The presence of MVI often influences the formulation of clinical treatment plans and postoperative efficacy. Surgical resection is the first choice for patients with HCC. Ideally, hepatectomy requires complete removal of the tumor while preserving adequate liver function. Using the Couinaud segmentation method, the surgeon can completely remove the tumors, the liver segment, and the micrometastases through the portal system. Previous studies have indicated that anatomical liver resection is the preferred option for patients with a high suspicion of MVI (15, 16). If patients have a low risk of MVI, local resection may be selected to reduce the risk of bleeding and infection, improving the short-term prognosis (17). Therefore, preoperative prediction, intraoperative management, and postoperative intervention for MVI have become research hotspots. However, the MVI detection rate relied on tissue sampling protocol which may fail to obtain the existing MVI (12). This study aimed to identify independent risk factors related to the occurrence of MVI, in order to provide clues identifying the patients with a high risk of recurrence. Our statistical analysis of 642 HCC patients revealed six independent predictive factors for MVI in HCC, particularly Edmondson-Steiner grade, capsule invasion, BDTT, AFP, tumor size, and NLR.

The occurrence of MVI is closely related to the tumor size (18). Pawlik et al. (9) found that tumor diameter was positively correlated with the incidence of MVI. This is consistent with the results of our study. Shi et al. (19) analyzed the pathological specimens of 113 cases of single HCC and found that the incidence of MVI significantly increased when the tumor diameter was >3 cm. In general, a larger tumor size often indicates a higher risk of MVI (20, 21). To prevent excessive loss of information, tumor size was treated as a continuous variable in our study. Regarding the relationship between tumor differentiation and MVI, some scholars believe that tumor differentiation is negatively correlated with the incidence of MVI (22). Our study concluded that Edmondson-Steiner grade and liver capsule invasion were independent risk factors for MVI in HCC. Tumor differentiation can only be determined by postoperative pathology, while tumor size and liver capsule invasion can be preliminarily assessed by imaging examination before surgery. Therefore, tumor size and liver capsule invasion may have a higher practical value in the preoperative diagnosis of MVI than the degree of tumor differentiation.

Currently, serum AFP level testing is one of the most common clinical laboratory procedures for the diagnosis of HCC. We chose AFP levels above 400 ng/ml as an important predictor of MVI, as revealed by previous research (23), and found that the MVI+ group had higher AFP levels than the MVI– group. Some studies have also shown that an AFP level over 100 ng/ml is an important indicator for predicting MVI (24). AFP levels are now widely regarded as a predictor of MVI, while the threshold of the AFP level used to predict MVI is still controversial.

According to previous reports, inflammation plays an important role in the occurrence, development, invasion, and metastasis of tumors (25). Many inflammatory markers in laboratory tests have been confirmed to have predictive value for the development of MVI (18, 25). The NLR was independently related to MVI, and this has been confirmed in a number of nomograms that calculated the predictive probability of preoperative MVI in HCC patients (26, 27). In our study, there was a significant difference in NLR levels between HCC patients with and without MVI. This is consistent with the results of previous studies. However, most of the inflammatory cell indicators in our cases were within the normal range, and these kinds of variables with a small range of numerical fluctuations depend on a large sample size to obtain more accurate results. The relationship between inflammatory response and the occurrence of MVI needs to be further investigated.

HCC with BDTT is rarely seen clinically, and the incidence of BDTT accounts for 1.2–9% of HCC (28). HCC with BDTT has aggressive characteristics, and its long-term prognosis is extremely dismal (29). A study reported that HCC patients with BDTT tended to have a higher probability of having MVI (30). We also found that BDTT is an important factor in predicting MVI. Due to the small sample size of patients with BDTT in this study, its value in predicting MVI needs further investigation.

In contrast with other studies, our study included patients from two centers and was constructed based on routine laboratory parameters that are more accessible and easily interpreted. However, our study has limitations as a retrospective study. First, although some individual factors such as Edmondson-Steiner grade were statistically significant, they can only be confirmed through postoperative pathology. This greatly limits the guidance significance of preoperative prediction models for treatment. Second, ~80% of patients were complicated with hepatitis virus infection in our study. Whether this model can be extended to other patients with HCC in Western countries is still unknown. It is still necessary to carry out multicenter, large-sample, prospective studies to achieve an accurate diagnosis of MVI and further explore its clinical significance.

In conclusion, we found that MVI influenced the prognosis in HCC and we analyzed independent risk factors for the occurrence of MVI. We hope that the results of this study will provide clues identifying the patients with a high risk of recurrence other than MVI alone.

The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding authors.

The studies involving human participants were reviewed and approved by the Ethics Committee of the Affiliated Hospital of Qingdao University and the Ethics Committee of the Beijing Tsinghua Changgung Hospital. Written informed consent for participation was not required for this study in accordance with the national legislation and the institutional requirements.

WY and ZC designed the study, analyzed the results, and wrote the manuscript. SC and WM provided strategic guidance. LL, LH, DY, SN, and LF collected the data. All authors commented on the manuscript, contributed to the article, and approved the submitted version.

This work was supported by the Shandong Higher Education Young Science and Technology Support Program (Grant Number 2020KJL005).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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