Hepatocellular carcinoma (HCC) is the leading malignant tumor from the liver, which is the seventh most common, and has the second highest death rate (in all 36 tumors) (1). It has already been reported in the article that the risk factor for poor prognosis is the lack of diagnosis of extrahepatic metastasis (EHM) (2). Therefore, an accurate evaluation of HCC metastases is critical for improved prognosis.

HCC is a kind of cancer that develops as a result of a secondary liver illness [such as viral hepatitis (HBV or HCV), alcoholic or fatty liver disease]. Liver function indices are intimately linked to the occurrence and development of HCC (3, 4). Besides, studies have reported that primary tumor progression characteristics (such as vascular invasion, tumor size and number, etc.) are independent risk factors for EHM (5, 6). The above parameters can be risk factors for metastatic HCC and will be included in this study as observational information. Since patients with HCC usually receive antitumor treatment during the clinical course, it may give a confounding effect on the analysis of metastatic factors. As a result, we evaluated the clinical features and risk factors of patients with HCC and EHM who did not receive anti-tumor therapy, and we created an effective EHM diagnostic nomogram.

The incidence of HCC has increased in many countries in recent years. The primary risk factors for HCC worldwide include chronic hepatitis B virus (HBV) or hepatitis C virus (HCV) and the consumption of aflatoxin-contaminated food. The prevalence of HCC caused by metabolic syndrome, obesity, diabetes, excessive alcohol consumption, and non-alcoholic fatty liver disease (NAFLD) is gradually increasing (8). Thus, as the etiology of the disease has changed, the risk factors for EHM of HCC may also be changed, and further research is required.

For patients with HCC with EHM, most previous studies examined only the relationship between clinicopathological characteristics and the prognosis of patients with HCC (5, 9–11). However, the common shortcoming was that the patients enrolled previously received anti-tumor treatment, and the lab results were incidentally altered (to exhibit low white blood cell counts, low platelet counts, poor liver or kidney function, and so on) (9), which may bring inevitable interference to the analysis of metastases. Therefore, this study investigated the clinical characteristics and risk factors of patients with HCC with EHM who did not receive anti-tumor treatment, and established an effective diagnostic nomogram for EHM. In our study, 28% (170) of all 607 HCC patients included had extrahepatic metastases, consistent with previous study results (9, 12). In the initially diagnosed patients, the metastatic sites included the lymph node (122, 71.8%), lung (104, 61.2%), bone (12, 7.1%), diaphragm (7, 4.1%), peritoneum (4, 2.3%), spleen (3, 1.8%), pancreas (2, 1.2%), adrenal gland (2, 1.2%), and stomach (1, 0.6%). The lung may be the most common site of EHM from HCC speciously, but in our study, the proportion of lymph node metastases was the highest (122, 71.8%). Additionally, a similar finding was obtained by another Chinese study (13). In that research study, among the 132 patients with extrahepatic metastases from hepatocellular carcinoma diagnosed by whole-body PET/CT, 72 (54.5%) had metastases in the lymph node, 32 (24.2%) had metastases in the bones, and 28 (21.2%) had metastases in the lungs. This may due to the main symptom of patients with simple lymph node metastases rarely present with clinical symptoms, and only a small proportion of patients are noted when the enlarged lymph nodes caused a compression effect, for example, the jaundice caused by bile duct compression. As a result, the rate of missed lymph node metastases was high and easily ignored in a relatively earlier stage of metastasis.

According to the univariate and multivariate analysis of EHM in our research ( Table 2 and Figure 2 ), there may be a potential relation between HCC patients with EHM and the tumor number. This relationship was also mentioned in another report which showed that the number of tumors >2 can be easier found in patients with EHM (14). They therefore concluded that the number of tumors could be associated with aggressive biological features. Coincidentally, in our research, the tumor counts are independent predictors for EHM ( Figure 2 ). Similar findings for HCC metastasis were noted previously, which revealed that a multiple tumor number was a risk factor for EHM in HCC (15, 16).

A close relationship between HCC size and EHM seems to exist according to our results ( Figure 2 ). One possible explanation is that the lager lesion contains more tumor stem cells, which are frequently identified as the source of malignant phenotypes such as aggressive growth, portal vein thrombosis, or metastasis. Another explanation is that the tumor biology changes beyond a certain mass, just as tumors in general cannot grow beyond a critical small size (9, 17, 18).

In this study, we also demonstrated that an elevated neutrophil was a significant independent predictor for EHM of HCC. Neutrophil is one of the most simple and effective markers of inflammation and is associated with poor prognosis in various cancers (11, 19, 20). Therefore, the immanent reason may be that the high neutrophil count is a symbol of an adequate environment for tumor progression, which has been shown to promote tumor growth and metastasis by secreting chemokines, vascular endothelial growth factor, and matrix metalloproteinase-9, which are involved in the development of local inflammation and angiogenesis (21–23).

Currently, angiopoietin-2 (Ang-2), microRNAs (miRNAs), and lncRNA BACE1-AS are available as a test for the evaluation of EHM in HCC (24–27). However, the above parameters are mainly laboratory-based and are not available in most hospitals. Therefore, our results identified the risk factors for EHM of HCC which are based on noninvasively clinically readily available data and developed a nomogram with some predictive ability. We constructed a predictive model of EHM of HCC by taking the above independent risk factors as variables. It is used to predict the initial probability of patient EHM, and validated internally and externally, confirming its certain predictive capacity for EHM. The calibration curves were drawn and showed that the nomogram predictions overlapped well with the actual clinical situation, with good agreement and credible prediction results.

In previous studies (9, 12, 14, 28), most researchers focused on the observation of the patient’s prognosis. Therefore, only a preliminary analysis of the reference indicators associated with EHM was performed. This study further explored the independent risk factors for EHM and developed a nomogram with some predictive ability, building on the previous work. It has a role to play in reducing missed EHM and designing optimal therapies for those patients. This study is a single-center study only and the model could be further improved with a larger sample size and multi-center data.

The original contributions presented in the study are included in the article/supplementary material. Further inquiries can be directed to the corresponding authors.

The study was censored on October 19,2020 and was approved by the Ethics Committee of The Affiliated Hospital of Qinghai University. All subjects signed an informed consent form. The patients/participants provided their written informed consent to participate in this study.

LZ is responsible for writing, LR, MQ, WW and XS are responsible for document of patients data. FY, MD and HW are responsible for document. following up, ZW, HF are responsible for guiding research and revising papers. All authors contributed to the article and approved the submitted version.

This study was supported by the National Natural Science Foundation of China (No. 82160466) and Research team for minimally invasive diagnosis and treatment of biliary and pancreatic diseases (The Affiliated Hospital of Qinghai University).

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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