Non-invasive tests for the prediction of primary hepatocellular carcinoma

Giovanni Marasco, Antonio Colecchia, Giovanni Silva, Benedetta Rossini, Leonardo Henry Eusebi,Federico Ravaioli, Elton Dajti, Luigina Vanessa Alemanni, Luigi Colecchia, Matteo Renzulli, Rita Golfieri,Davide Festi

Abstract

Key words: Non-invasive test; Fibrosis-4 index; Hepatocellular carcinoma; Liver stiffness measurement; Spleen stiffness measurement; Albi

INTRODUCTION

Hepatocellular carcinoma (HCC) is the most common primary liver cancer,representing about 90% of the cases[1]. It is the fifth most common malignant tumor in the world and the third most frequent cause of cancer-related death globally, with more than 600000 deaths per year[2-5]. Liver cirrhosis represents a major risk factor for HCC; indeed, 90% of hepatocellular carcinomas are related to cirrhosis and one-third of cirrhotic patients develop HCC during their lifetime[2,5].

The major driver of the HCC development is the degree of liver fibrosis, historically assessed with a semi-quantitative histologic evaluation[6,7], even though sampling variability and underrepresentation of liver biopsy[8]hampers its robust determination[9]. Exceptions to this postulate are mainly represented by HCC arisen in hepatitis B[10]and non-alcoholic fatty liver disease[11], since their carcinogenetic mechanisms are less dependent on liver fibrosis. Nowadays liver biopsy, previously considered the diagnostic method of choice for evaluating liver fibrosis, is a procedure confined only to specific and limited diagnostic questions in complex liver diseases[12].Indeed, several limitations for its extensive use have been reported, besides the need for physician and pathologists with high expertise, it is a costly and invasive procedure[12].

Moreover, HCC develops more frequently in patients with cirrhosis complicated by portal hypertension (PH), since PH plays an important role in liver carcinogenesis.Currently, the measurement of the hepatic venous pressure gradient (HVPG)represents the gold standard method for predicting the progression of cirrhosis and the occurrence of its complications, including HCC[13,14]. Only two studies explored the predictive role of HVPG for primary HCC development; in the first by Ripollet al[14]the authors concluded that an HVPG ≥ 10 mmHg was able to predict primary HCC development; in parallel, Kimet al[15]in a cohort of alcoholic liver disease patients also concluded that HVPG can be used to predict the development of HCC. However,HVPG is an invasive and risky method and it is not available in all liver units. For these reasons, several research groups have proposed to use non-invasive tools (NITs)as an alternative to liver biopsy and HVPG for predicting the development of primary HCC. The increasing need for NITs in several scenarios of patients with liver cirrhosis has also been recently addressed by the guidelines of the European Society for the Study of the Liver[12]. The aim of this review is to summarize the available literature on the recent advances in the evaluation of the different non-invasive tests for predicting primary HCC occurrence.

BIOCHEMICAL-BASED NITs

Aspartate aminotransferase to platelet ratio index

The aspartate aminotransferase (AST) to platelet ratio index (APRI) is a biochemical score which has a potential utility in predicting the risk of primary HCC[16]. The APRI was introduced by a study by Waiet al[17]and can be calculated using the following formula: AST (UI/L) × [100/platelet count (103/mm3)]. In a meta-analysis on hepatitis C virus (HCV)-patients pooling data on APRI, an APRI value ＞ 1.5 had the greatest predictive value for diagnosing cirrhosis, whereas a value ＜ 0.5 for ruling-out the presence of cirrhosis[18]. Thus, this score was developed as a non-invasive predictor of the progression to fibrosis in patients with chronic viral hepatitis. Over the years,several studies validated its role as markers of hepatic fibrosis[19,20]and subsequently tested its ability in predicting HCC (Table 1)[16,20-39].

One of the first correlation between APRI and HCC development was assessed by Hannet al[34]among hepatitis B virus (HBV) patients; APRI was shown to be a good prospective predictor of HCC, especially in the multivariate analysis (Ptrend =0.008 in quartile analysis). In a later study by Kimet al[36]including 542 HBV patients, the authors reported an area under the receiver operative characteristic (AUROC) of 0.731 for APRI in predicting HCC, using a cut-off of 0.766.

In a study by Chenet al[35]the authors reported at multivariate analysis a prognostic role for APRI in both patients achieving or not sustained virologic response (SVR) in patients treated with peginterferon/ribavirin: In particular a post-treatment APRI ≥0.5 was associated with a hazard ratio (HR) of HCC development of 4.401 in SVR patients, whereas an APRI ≥ 1.5 with an HR of 10.905 in not SVR patients. Similarly, Jiet al[24]analyzed HCV patients who had achieved SVR after interferon-based antiviral treatment, showing that a post-treatment APRI ≥ 1.5 was associated with a higher incidence of HCC (P＜ 0.01). On the other hand, as new direct antiviral agents (DAA)are available, APRI index is lowered after the achievement of SVR[40], but still holds its predictive value in for HCC occurrence, even after SVR[29].

The prognostic value of APRI has been reported also in other settings beyond viral hepatitis. Kimet al[26]reported in a cohort of patients with alcoholic liver cirrhosis an AUROC of 0.61 for predicting HCC occurrence at 3 years. Cheunget al[22]also investigated the link between APRI and HCC development in patients with primary biliary cholangitis treated with ursodeoxycholic acid: An APRI at 1 year after treatment (APRI-r1) ＞ 0.54 resulted as an independent risk factor for HCC (HR = 3.94,P= 0.043) with an AUROC of 0.77. In conclusion, since APRI cut-offs for cirrhosis suffers of poor sensitivity it is very likely that also the predictive role for HCC development could be underestimated[41]. Several authors recommended APRI should be considered when liver stiffness measurement (LSM) is unavailable. On the other hand, in such conditions when a transaminase flare could be expected, the use of APRI is rather recommended[42]. However, we advise the use of this simple transaminase-based NIT which allows us to detect significant fibrosis and to stratify the risk of HCC only in resource-limited settings.

Fibrosis-4 index

The fibrosis-4 index (Fib-4) index was firstly proposed by Sterlinget al[43]in a human immunodeficiency virus (HIV)/HCV cohort to assess the degree of hepatic fibrosis and it is based on four factors, included in the following equation: [age (years) × AST(UI/L)]/[platelet count × ALT (UI/L)]. A Fib-4 ＞ 3.25 had a high specificity for rulingin cirrhosis, while a value ＜ 1.45 was the cut-off to rule-out cirrhosis.

As far as Fib-4 is concerned, various authors[44-48]have assessed its predictive value for primary HCC development (Table 2)[16,20,23,25-27,32,36,44-60].

Tsenget al[48]evaluated if Fib-4 was able to rule-out HBV patients at lower risk of HCC development; considering treatment-na?ve patients, those with a baseline Fib-4＜ 1.29 had a significantly lower HCC risk, compared to those with baseline Fib-4 values ≥ 1.29 (HR 5.56, 95%CI: 3.93-7.86). Among patients who received nucleoside analogues (NUC) treatments, none of 326 subjects with baseline Fib-4 ＜ 1.29, ALT ＜ 40 U/L, and HBsAg ＜ 1000IU/mL developed hepatocellular carcinoma. Therefore, a cutoff value of Fib-4 ＜ 1.29 showed a good prognostic performance.

Interesting results were also reported in two different studies by Suhet al[46,47]. The first one was conducted on chronic hepatitis B carriers[46]: It was observed that,compared to subjects with Fib-4 ＜ 1.25, subjects with Fib-4 between 1.7 and 2.4 had an adjusted HR of 4.57 (95%CI: 1.50-13.92), and subjects with Fib-4 ≥ 2.4 had an aHR of 21.34 (95%CI: 7.73-58.92) for HCC occurrence. In addition, Fib-4 was shown to have incremental predictive value to US-liver cirrhosis for HCC development (C-index:0.701vs0.831,P= 0.001). Fib-4 resulted also a better predictor of HCC incidence,compared to US-liver cirrhosis (C-index: 0.775vs0.701,P= 0.040).

Kanwalet al[45]evaluated a cohort of subjects with HCV-related disease, previously treated with DAAs reaching SVR; the group with Fib-4 ＞ 3.25 showed an annual HCC incidence of 2.16%, against 0.45% among those with Fib-4 ranging from 1.45 to 3.25,and 0.3% of those with Fib-4 ≤ 1.45. Similar results came from a very large study from North America[56]exploring Fib-4 variations after SVR: a decrease in Fib-4 scores from≥ 3.25 pre-SVR to ＜ 3.25 post-SVR halved the risk of HCC. Interestingly, in thisstudy[56]even in patients without cirrhosis and with a low risk of HCC, a pre-SVR Fib-4 score ≥ 3.25 (HCC risk 1.22%/year) and post-SVR Fib-4 scores ≥ 3.25 (HCC risk 2.39%/year) were associated with a high risk of HCC up to 10 years after SVR.

Table 1 Studies reporting the role of aspartate aminotransferase to platelet ratio index in predicting hepatocellular carcinoma

The same cut-off values used by Kanwalet al[45]were applied in a study by Parket al[44]which studied patients with HIV infection, most of whom had also HBV/HCV infection or history of alcohol abuse; in this cohort, the elevation of Fib-4 proved to be a strong predictive factor for HCC development (HR 3.6 for Fib-4 1.45- 3.25; HR 9.6 for Fib-4 ＞ 3.25;P＜ 0.0001).

The second study of the aforementioned by Suhet al[47]was conducted on alcohol drinkers: compared to patients with Fib-4 values ＜ 1.00, patients with Fib-4 values ≥1.75 and ＜ 2.10 and patients with Fib-4 values ≥ 2.10 showed an aHRs of 5.18 (95%CI:1.12-24) and 13.63 (95%CI: 3.77-49.33), respectively, for HCC development. Similarly,Fib-4 was a better predictive tool for HCC development if compared to US-assessed liver cirrhosis (C-index, 0.665vs0.527,P= 0.044).

As non-alcoholic fatty liver disease (NAFLD) is concerned, a study[57]from four European primary care databases representing the UK, the Netherlands, Italy and Spain, including 18 million adults, found that patients with NAFLD and non-alcoholic steatohepatitis (NASH) with high Fib-4 (＞2.67) score had an increased risk for HCC development compared to those with low Fib-4 (HR 25.2).

From a critical point of view, similarly to other serologic markers used in the evaluation of liver fibrosis, Fib-4 has some limitations, mainly because the index is influenced by age, race and could underestimate the presence of fibrosis inNAFLD[61,62]. Nevertheless, since it seems to be the most widely validated score for predicting cirrhosis and HCC, we still support its use as general and simple screening for the risk of HCC during the everyday clinical practice in the main settings of the liver cirrhosis as HBV, HCV and NAFLD/NASH patients.

Table 2 Studies reporting the role of fibrosis-4 index in predicting hepatocellular carcinoma

APRI and Fib-4 comparative studies

Several research groups performed comparative studies on the ability of APRI and Fib-4 in predicting HCC; most of them have reported that both Fib-4 and APRI may be used together as predictors of HCC development to improve their predictive accuracy and to overcome the above-mentioned limitations of each score. For example, Paiket al[16]stratified more than 1000 HBV patients into three groups: those with both APRI and Fib-4 above the proposed cut-off values, 0.5 and 1.45 respectively(Group 1), those with only one index above cut-offs (Group 2), and those with both indexes below (Group 3): They showed that hepatocellular carcinoma had highly different incidence rates in the 3 groups (13.9% in Group 1, 1.4% in Group 2, 1.2% in Group 3,P＜ 0.001); similarly, in the non-cirrhotic population the rates were 11.4% for Group 1, 1.5% for Group 2 and 0.4% for Group 3 (P＜ 0.001). This research suggested that the combined use of APRI and Fib-4 can be effective in stratifying the HCC risk and it may be preferred to the use of a single test[16]. Besides, Naet al[20]identified both APRI and Fib-4 as independent predictive tools for HCC in patients with chronic hepatitis C responsive to Interferon therapy. Indeed, the annual incidence of carcinoma was significantly higher in those patients with a post-treatment APRI 0.5(1.67%vs0.07%,P＜ 0.0001), as well as in those with a post-treatment Fib-4 ≥ 2.5 (1.49vs0.01,P= 0.0003). As regards to the HCV and the DAA setting, although a previous study[29]on a small cohort of patients did not find at multivariate analysis a predictive role for Fib-4 and APRI, a recent larger evaluation in the above-mentioned study by Kanwalet al[45]found that persistently high Fib-4 and APRI after HCV-eradication in both patients with and without cirrhosis was associated with an increased risk of HCC development.

Finally, a study by Peleget al[55]in NAFLD patients explored the accuracy of APRI and Fib-4 in predicting the development of various malignancies (including HCC):The results showed that, with adjustments for gender, age, hypertension and type 2 diabetes, an APRI score ＞ 1.5 (HR 4.94, 95%CI: 1.92-12.82,P= 0.0009) and a Fib-4 score ＞ 2.67 (HR 6.12, 95%CI: 2.31-16.17,P= 0.0003) were associated with the occurrence of malignancies. Thus, according to recent publications, both APRI and Fib-4 can have a potential utility in predicting primary HCC development, with increased accuracy when combined. However, further research should be carried out to confirm these data in all the different liver disease aetiologies and to better explore the role of APRI and to define its best cut-off values, even though in most of the above-mentioned studies the predictive accuracy remained rather low. On the other hand, stronger data are available for the use of Fib-4 in the setting of HBV also during NUC therapy, in NAFLD as general screening of HCC risk and in HCV before and after eradication for a predictor of the risk to select patients that require long term surveillance.

Forns index

The index developed by Fornset al[63]in 2002, before the introduction of transient elastography techniques was first proposed as a non-invasive tool for the detection of patients with non-significant liver fibrosis. It is calculated using four variables (age,gamma glutamyl transferase levels, total cholesterol levels and platelet count), with the following formula: 7.811 - 3.131 × ln [platelet count (109/L)] + 0.781 × ln [gamma glutamyl transferase (IU/L)] + 3.467 × ln [age (years)] - 0.014 × [cholesterol (mg/dL)].The first studies on Forns index (FI) highlighted its accuracy in identifying patients with different stages of fibrosis and cirrhosis[63,64]. In recent years, some authors have also tried to evaluate the usefulness of this score for HCC prediction. A study by Toyodaet al[21], conducted on HCV patients responsive to antiviral therapy, evaluated the efficacy of various fibrosis markers (FI, APRI and Fib-4) to detect patients with low risk of developing HCC after SVR. All three scores performed well, but pretreatment FI seemed to be the most accurate one; patients with a FI ＜ 5.34 had a significantly lower HCC incidence compared to those with values above 5.34 (P=0.0012). Besides, no subjects with low FI developed HCC after SVR, whereas HCC occurred both in patients with low APRI (9 cases) and patients with low Fib-4 (5 cases). These results showed that baseline FI (calculated before antiviral therapy) may be used to detect patients who can end the HCC surveillance program after the eradication of HCV.

Other significant findings were reported by D'Ambrosioet al[65], who carried out a prospective study on patients who achieved SVR after interferon therapy (n= 38); the univariate analysis showed that FI ＞ 6.9 resulted as a risk factor for HCC development(HR 12.8, 95%CI: 1.14-143.9;P= 0.039).

FI has shown promising results, but its value needs to be confirmed by further studies, with a higher number of HCC cases and in other aetiologies than HCV.However, the overall feeling is that FI is still mainly used for fibrosis assessment and has not easily entered clinical practice perhaps because of its complexity since it includes the evaluation of serum cholesterol which is not routinely performed in all centers.

Lok index

The Lok index is a non-invasive tool introduced by an American research group[66]as a predictor of cirrhosis development in patients with chronic hepatitis C. This index is based on simple laboratory parameters and it is calculated with the following formula: Log odds (predicting cirrhosis) 5.56 - 0.0089 × platelet count (103/mm3) +1.26 × AST/ALT ratio + 5.27 × INR. Recently, a potential role of Lok Index in predicting HCC development has been explored. A retrospective study by an Egyptian group[67]analyzed the performances of eight different biochemical scores(King score, Fibro Q, AST-ALT ratio, APRI, Lok index, Goteborg University Cirrhosis Index, Fibro Alpha, and Biotechnology Research Center). The results showed a quite significant correlation between an increased Lok index (≥ 2.4) and HCC development(sensibility = 57.1%, specificity = 65.7%, with an AUROC = 0.66); however, the prognostic accuracy of this score proved to be worse than other indexes, especially the Fibro Alpha and the Biotechnology Research Center (AUROC 0.91 and 0.93 respectively), and not sufficient to propose it as a valid predictive tool. Interesting results were also reported in the previously mentioned study by D'Ambrosioet al[65],conducted on subjects who achieved SVR for HCV; the analysis showed that a post-SVR Lok index ＞ 0.5 was correlated with an increased risk of developing HCC (HR 6.24, 95%CI: 1.03-37.6;P= 0.046); in the HCC population, 3 out of 5 patients had Lok index ＞ 0.5, whereas in the not-HCC cohort, only 5 out of 33 patients had Lok scores ＞0.5 (P= 0.05). This study demonstrated that, in a subset of cirrhotic patients, the HCC risk remains high even after SVR, and this aspect may be detected using the Lok index, as well as the FI. Despite some promising results, at present the Lok score is predominantly used for the prediction of cirrhosis; further trials with larger cohorts are needed to deeper explore its role as an HCC predictor in the different liver disease cohorts beyond HCV.

Albumin-bilirubin and platelet count-albumin-bilirubin scores

Another biochemical index used in clinical practice is the albumin-bilirubin (ALBI)score, introduced by Johnsonet al[68]to evaluate liver function in patients with hepatocellular carcinoma. It was initially proposed as an alternative to the Child-Pugh score to overcome some of the known limitations, such as the inclusion of nonobjective parameters (ascites, encephalopathy). The ALBI score is based on serum levels of albumin and total bilirubin and can be calculated with the following formula:(log10 bilirubin [μmol/L] × 0.66) + (albumin [g/L] × -0.0852). Johnson and colleagues also proposed to stratify ALBI values into three grades (ALBI ≤ -2.60: Grade 1; ALBI ＞-2.60 and ≤ -1.39: Grade 2, ALBI ＞ -1.39 : Grade 3), that were associated to different outcomes[68]. Subsequently, other studies highlighted the accuracy of the ALBI score in assessing the liver function in subjects with HCC undergoing resection or other treatments (transarterial chemoembolization, transarterial radioembolization, thermic ablation)[69-72]. This score proved to be effective in predicting the patient's clinical outcome, especially in terms of hepatic decompensation (HD) and post-treatment survival. More recently, an Italian research group[73]observed that, in a cohort of HCV patients treated with DAA therapy, an elevated ALBI score before DAA treatment was strongly correlated with the occurrence of HCC (HR: 2.35, 95%CI: 1.05-5.25,P=0.038). According to Johnson's cut-offs[68], subjects with ALBI grade 2 or 3 showed a significantly higher risk of developing HCC than those with ALBI grade 1 (HR 2.71,95%CI: 1.08-6.83,P= 0.01).

A more recent study by Fujitaet al[74]evaluated the HCC-risk of 125 prospectively collected HCV patients, identifying 3 categories with different HCC-risk according to ALBI percentile distribution, which are from that at lower to higher risk: Q1 with ALBI score below -2.773, Q2 with ALBI score between -2.773 and -2.215 and Q3 with ALBI score above -2.215 at baseline (P＜ 0.05). More importantly, low ALBI scores at baseline inversely correlated with the HCC-free survival of the patient. Another model, the platelet count-albumin-bilirubin (PALBI) score, has been developed by integrating the platelet count, which acts as a surrogate for the degree of portal hypertension, into the ALBI score. This marker has proved to be a valid predictor of the overall survival among patients with HCC undergoing various treatments, such as resection, ablation or radiotherapy[75-77]. Other authors[78,79]have also reported that the PALBI score can be used to predict the outcome of both patients with decompensated cirrhosis and subjects with liver-related complications. However, at present, there is no available data about the application of the PALBI score in predicting the development of primary HCC. In conclusion, to date only a few studies evaluated the predictive role of ALBI score for HCC development and its use is limited as prognostic markers after HCC treatment; this could be due to the fact that this score provides an objective estimation of the hepatic reserve estimation not completely taking into account the carcinogenetic mechanisms related to advanced cirrhosis and portal hypertension. Moreover, ALBI scores variations are more likely in advanced stages of liver cirrhosis, when HCC is already expected.

Indocyanine green retention test

The indocyanine green retention test (ICG R15) is a widely-used method for the evaluation of hepatic function[80,81]. This test is based on the intravenous injection of a contrast agent, the ICG, which is eliminated by the bilious system. Fifteen minutes after the injection, the agent's clearance is assessed: In subjects with preserved liver function, the retention rate of ICG is normally lower than 10%; a retention value above 10% indicates a reduced hepatic function. At present, this test plays a central role in the pre-operative assessment of HCC patients undergoing resection and helps surgeons plan the extent of hepatectomy.

Several studies[82,83]highlighted that ICG R15 could be used to detect, among patients with compensated cirrhosis, those at higher risk of developing portal hypertension and esophageal varices. Therefore, this test was proposed as a noninvasive tool to identify patients who need endoscopic surveillance. The study by Lisottiet al[84]underlined the correlation between high ICG R15 values and the occurrence of HD in subjects with cirrhosis and PH. It is worth mentioning that patients with an ICG R15 ＞ 23% showed an HD incidence of 70% in the first 3 years after the evaluation; furthermore, 18 out of 134 patients developed an HCC during the follow-up period, while twelve of them had previously experienced at least one episode of HD.

Another study by Songet al[85]showed that ICG R15 ＞ 10% is an independent risk factor for HCC recurrence in patients who underwent resection; in fact, subjects with ICG R15 ＞ 10% had lower recurrence-free survival rates than the rest of the population. However, in literature there is no experimental data focused on the performance of ICG R15 in predicting primary HCC even if promising data have been highlighted in the setting of HCC recurrence. However, multiple confounding factors are involved in ICG flow and metabolism[86], and in addition, if compared to other available NITs it seems to be more inquiring, thus, we do not advise its routine use in HCC-risk assessment.

ULTRASOUND BASED NITs

Liver stiffness measurement

In recent years, the measurement of liver stiffness using transient elastography(FibroScan?; Echosens, Paris, France) has been used to assess the degree of hepatic fibrosis and thus to evaluate the risk of related complications[87-89]. In the last decade,research was also focused on the correlation between LSM and HCC development.Studies reporting this correlation are reported in Table 3[49,60,89-120]. Several crosssectional trials[89,110,117]demonstrated that the median values of liver stiffness in patients with HCC are significantly higher than in those without HCC.

One of these large prospective trial by Poynardet al[96](n= 3927) on chronic hepatitis C patients found that LSM was predictive of severe liver-related complications (AUROC 0.77;P＜ 0.0001), including primary HCC (AUROC 0.86;P＜0.0001). Other authors tried to quantify with LSM the risk of developing primary HCC after DAAs therapy. Rinaldiet al[111]found that an LSM cut-off value of 27.8 kPa at baseline before treatment identified patients at high risk of HCC after DAA, whereas Corma-Gómezet al[121]found in an HIV/HCV cohort treated with DAA that also Fib-4 in addition to LSM was associated with HCC occurrence. Another recent study[60]carried out in patients undergoing DAA therapy found that baseline LSM ＞ 30 kPa independently predicted de novo HCC, with a 3-year estimated incidence of 20% in these patients versus 5% in patients with LSM ≤ 30 kPa. In the same study, in a model without LSM but including LSM-spleen to platelet ratio score and Fib-4, the latter was found to be independently associated with de novo HCC occurrence.

Nevertheless, all these studies only highlighted this “static” phenomenon, without analyzing the “dynamic” correlation between the progression or regression of hepatic fibrosis and the risk of developing HCC. Because of this limitation, several longitudinal prospective studies have been recently conducted. The first one,published by a Japanese group on a large cohort of 866 subjects with chronic C hepatitis[115], proved that an LSM value ＞ 10 kPa is an accurate predictor of increased HCC risk (LSM values 10.1-15 kPa, HR 16.7; LSM 15.1-20, HR 20.9; LSM 20.1-25, HR 25.6; LSM ＞ 25 kPa, HR 45.5; all withP＜ 0.001). In another prospective study carried out by Junget al[90]on HBV patients it was noticed that subjects with LSM ＞ 8 kPa had an increased HCC risk, and that the incidence of HCC was directly proportional to LSM values: for LSM 8.1-13 kPa, HR 3.07 (P= 0.047); for LSM 13.1-18 kPa, HR 4.68 (P= 0.012); for LSM 18.1-23 kPa, HR 5.55 (P= 0.009); for LSM ＞ 23 kPa, HR 6.60 (P=0.004). After a median follow-up of 18 mo, a second LSM was made to evaluate if changes over time were related to a variation in HCC risk: Patients with baseline LSM≤ 13 kPa and follow-up LSM ＞ 13 kPa had a significantly higher incidence of HCCthan those with both values ≤ 13 kPa (P＜ 0.001); on the contrary, subjects with baseline LSM ＞ 13 kPa who experienced regression of LSM below 13 kPa during follow-up had a significantly lower incidence of HCC than those who maintained an LSM value ＞ 13 kPa (P＜ 0.001). Therefore, this study demonstrated that LSM can be also used as a “dynamic” predictor of HCC risk, since its changes over time cause variations in the probability of developing HCC. This dynamic aspect has also been studied by our research group, which evaluated liver stiffness in HCV patients before and after DAAs therapy[122]. The results of our study showed that subjects who developed HCC had a lower reduction of LSM (ΔLS) than the rest of the cohort (-18.0%vs-28.9%,P= 0.005); a ΔLS ＜ 30% resulted as an independent risk factor for HCC development at multivariate analysis. Another recent study on this topic,recently published by Ponset al[113], found that LSM ＜ 10 kPa (HR 0.33; 95%CI: 0.11-0.96) and albumin levels (HR 0.08; 95%CI: 0.02-0.25), both evaluated during follow-up,were independently associated with the risk of HCC; moreover, the group with a combination of these two predictors led to an HCC incidence ratio ≥ 1.9/100 patient years.

Table 3 Studies reporting the role of transient elastography in predicting hepatocellular carcinoma

LSM has also been compared with other NITs. Chonet al[49]compared the performance of LSM in predicting HCC with other indexes, such as LSPS, APRI and Fib-4; among all, LSM proved to be the most accurate model (AUROC 0.789).

Since the epidemiology of the liver disease is rapidly changing in the last decade due to the outbreak of new antiviral therapies and changing in the general population lifestyle, increased attention has been addressed to the evaluation of the prognostic significance of NITs in non-alcoholic fatty liver disease/steatohepatitis. A Japanese study[112]including cACLD patients with different aetiologies found that in NAFLD patients the incidence of HCC development was significantly higher among those with LSM≥ 5.4 kPa and CAP ≤ 265 dB/m than among others (HR 8.91, 95%CI: 1.47-67.97,P=0.0192). A further study[123]on NAFLD patients was not able to find a cut-off value for HCC prediction, even though the authors reported an increased incidence of HCC with increasing LSM (＜ 12 kPa: 0.32%; 12-18 kPa: 0.58%; 18-38 kPa 9.26% and ＞38 kPa: 13.3%).

In conclusion, LSM is a good prognostic test, better than other liver fibrosis NITs,for HCC development prediction in chronic liver disease due to different aetiologies.Notably, a repeated assessment over time of LSM in cirrhotic patients could be more accurate than a single evaluation in monitoring the risk of HCC, even after viral eradication.

LSM-spleen to platelet ratio score

The LSM-spleen to platelet ratio score (LSPS) is a biochemical index obtained using the following formula: LSM (kPa) × spleen diameter (mm)/platelet count. This score was firstly proposed as a predictive tool for high-risk oesophageal varices in patients with HBV-related cirrhosis[124], and thus also as a surrogate marker of portal hypertension. Subsequently, various authors[49,125,126]have highlighted the relationship between an elevated LSPS and an increased risk of developing primary HCC. In a study by Shinet al[125]on 227 subjects with chronic HBV infection, the 18 patients who developed HCC averagely had higher LSM values, a longer spleen diameter and a lower platelet count than the rest of the study population (allP＜ 0.05). In addition, a LSPS of 1.1-2.5 was associated with a HR of 2.0 (P= 0.032) for HCC and a LSPS ＞ 2.5 implied an HR of 8.7 (P= 0.002)[125]. Other important results have been reported by Marzanoet al[126], who enrolled HBV patients responsive to nucleot(s)ide analogues:Subjects with a post-therapy LSPS ＜ 0.62 showed a significantly lower incidence of HCC compared to those with values ≥ 0.62 (7%vs36%,P= 0.001)[126]. Antiviral therapies generally lead to the regression of cirrhosis and to a lower incidence of complications in this kind of patients[127]. The study also showed that low LSPS values at the end of the therapy were related to a lower risk of HCC occurrence, as well as to more significant regression of portal hypertension. In the previously mentioned study by Chonet al[49], various scores were evaluated as HCC predictors in patients with chronic hepatitis B: LSM and LSPS (AUROC = 0.789 and 0.788, respectively) showed better predictive performances than APRI, age-spleen-to-platelet ratio index, P2/MS,and Fib-4 (AUROC = 0.729, 0.756, 0.696, and 0.744, respectively). However, at multivariate analysis, LSM resulted as the only independent predictor of HCC (HR =1.040,P= 0.006), whereas LSPS was not significant (HR 1.002,P＜ 0.05). Therefore,these good results on LSPS could be explained by the ability of both LSM and spleen to platelet score to evaluate either the degree liver fibrosis and the additional carcinogenetic mechanisms added by portal hypertension in advanced chronic liver disease. However, further validation studies of these scores are still needed.

Spleen stiffness measurement

During the last decade, the use of transient elastography has been extended to the measurement of spleen stiffness. This organ, differently from the liver, is involved in the hemodynamic modifications due to PH even at higher values of portal pressure.The level of spleen stiffness (SS) is, therefore strictly related to the degree of PH even for HVPG values above 10-12 mmHg[128,129]. Several studies highlighted an excellent correlation between SS measurement (SSM) and the degree of PH assessed by HVPG[130,131]. Several reasons could explain this phenomenon. Firstly, the position of the organ allows a downstream of the portal circle, the elevation of portal pressure causes a blood reflow through the splenic vein, which leads to spleen's congestion;secondly, the abnormal portal pressure induces structural modifications of the spleen(such as hypertrophy of the red pulp) as well as the development of a hyperdynamic circulation, both factors that play a role in the increase of spleen stiffness[132-134]. Recent studies[135-137]have shown the excellent performance of SSM in predicting the presence of oesophageal varices[138-142]and the risk of cirrhosis-related complications. Colecchiaet al[135]conducted a prospective study including patients with compensated cirrhosis finding that SSM ＞ 54 kPa was able to predict the development of HD during followup, including ascites, variceal bleeding, encephalopathy and HCC. In the HCC setting, the same group[143]found that an SSM ＞ 70 kPa was the only independent predictor of late HCC recurrence (more than 24 mo) after resection of primary HCC.The correlation between increased SSM and the development of HCC is probably based on the role of portal hypertension. Indeed, it has been demonstrated that PH causes alterations in the portal circle, such as intrahepatic shunts, veno-occlusive thrombotic lesions and sinusoidal capillarization, which lead to lower sinusoidal perfusion[144]. This local ischaemic condition may cause the production of HIF(hypoxia-induced factor) and other cytokines, which stimulate neo-angiogenesis and fibrogenesis in dysplastic nodules[145]; the proliferation of new blood vessels and the progression of fibrosis favour the carcinogenesis process. Thus, SSM can be considered a promising method, with better performances than LSM in assessing the PH degree. However, to date, no studies directly evaluated the role of SSM in predicting primary HCC.

CONCLUSION

Several prognostic models based on NITs have recently been proposed as HCC predictors in experimental trials. However, the evidence that non-invasive tests can easily and accurately predict the risk of developing hepatocellular carcinoma in clinical practice is still scarce.

The most reliable data is available on LSM which accurately reflects the severity of the liver disease. LSM is able to evaluate either liver fibrosis degree, inflammation and portal hypertension, which are the main pathogenetic players of HCC development and risk. Furthermore, LSM can be used dynamically for monitoring HCC risk over time in cirrhotic patients. However, more studies are needed to validate LSM results on different aetiologies, such as NAFLD, and to determine specific optimal cut-off,able to assess HCC risk for each etiology. Moreover, the predictive role of other NITs should be further investigated. Despite these limitations, NITs represent valid tools helping clinicians in their daily practice, and they soon may also play a role in implementing surveillance strategies for HCC.