Hepatocellular Carcinoma In Non Cirrhotic Liver

Published Date: 02 Nov 2017

Abstract

HCCs arising in non-cirrhotic livers are unique and have characteristic demographic distribution and etiology. In contrast of its counterpart in cirrhotic liver; these HCCs do not show stepwise regenerative nodule-dysplastic nodule-HCC carcinogenesis, rather develop de-novo. In general there is lower prevalence of the three major risk factors for HCC (hepatitis B and C virus infections and alcohol abuse) in these patients. They are often detected in an otherwise healthy individual without a known liver disease or altered AFP. Interestingly, they are diagnosed at an advanced stage and have larger tumor burden but are often amenable to hepatic resection and have better overall and disease free survival.

Alterations in cell cycle regulators, oxidative stress and the presence of increased levels of pro-tumorigenic growth factors play key roles in the etiopathogenesis.

An early and timely diagnosis may play a critical role in the treatment and overall prognosis. The aim of this review article is to provide a comprehensive and contemporary review of genetics, pathology, imaging findings and natural history of HCC in non-cirrhotic liver.

Introduction

Hepatocellular carcinoma (HCC) is the most common (85%–90%) primary hepatic malignancy and 3rd most common cause of cancer mortality worldwide[1]. HCC usually (60-90%) arises on the background of cirrhotic liver due to hepatitis or alcoholism. However, approximately 10-20% HCCs may occur in non-cirrhotic liver; the actual prevalence may vary between 7%- 54% in varying with geographic location[2].

Compared to HCC in cirrhotic liver, the HCC arising in non-cirrhotic liver (NC-HCC) is a distinct clinical entity because it occurs in younger age group, demonstrates a lower male to female ratio, and most often presents as a large and solitary tumor. Despite the fact it is diagnosed with large tumor burden it remains amenable to hepatic resection. Genetically, instead of following a classical step wise carcinogenesis pattern, they exclusively illustrate de-novo carcinogenesis.

NC-HCC commonly occurs on a background of chronic hepatitis, metabolic syndromes, or variety of hereditary disorders. Alterations in cell cycle regulators, oxidative stress and the presence of increased levels of pro-tumorigenic growth factors play key roles in the etiopathogenesis of the NC-HCC.

Epidemiology

HCC is 5th most common cancer in men and the 8th most common cancer in women worldwide, and has been attributed as fastest growing cause of cancer-related deaths in the United States.

In general, the HCC shows some male predominance with a male to female ratio ranging from 3.2- 8.1 and affects elderly population with a unimodal age distribution, peaking at the 7th decade[3]. NC-HCC on the contrary shows a lower male predilection with a ratio of 1.3-2.1 and elucidates a bimodal age distribution with a peak at second and seventh decades of life[4, 5]. Interestingly, the first peak (adolescents and young adults) actually encompasses vast majority of fibrolamellar carcinoma (FL-HCC) and shows almost identical gender distribution. FL-HCC is a distinct variant of HCC and not associated with hepatitis or cirrhosis[6].Geographically, FL-HCCs demonstrate predilection for Europe and North America but uncommon in Asia and Africa.

Clinical Presentation

Most of the patients with NC-HCC are otherwise healthy or the status of the chronic liver disease is unknown. Unlike their counterpart in cirrhotic livers, the patients with NC-HCC do not undergo routine surveillance and the tumor is often detected at an advanced stage. Therefore, about 70% of the patients with NC-HCC have a symptomatic presentation [3, 7], which are attributed to the grown large sized tumor.

Clinical signs and symptoms are non-specific and common clinical symptoms in descending order include abdominal pain (52%) or distention (9%), weight loss (9%), anorexia (6%) and chest pain (6%)[8]. Other symptoms may include asthenia, malaise, and fever. However, the patients may be asymptomatic or may present with abnormal liver function tests; however, the frequency of jaundice is much lower. Rarely hemoperitoneum due to tumor rupture can be a life threatening presentation[9].

Pathology

The non-tumorous liver parenchyma in the patients with NC-HCC commonly demonstrate changes related to chronic hepatitis, varying degrees of fibrosis, steatosis, iron overload or other metabolic disorders. NC-HCCs are often solitary, large (~10cm), un-encapsulated, well circumscribed and softer in consistency, which is conflicting to classical HCC.

According to histological classification criteria of the World Health Organization (WHO), the trabecular type is the most common form (41–76%) in non-cirrhotic HCCs, as it is in cirrhotic subjects. The schirrous type and the mixed hepatocholangiocarcinoma are rarely found, but tend to be more frequent in a non-cirrhotic background, whilst FL-HCC is almost exclusively limited to non-cirrhotic livers (11% vs. 1.5%).

FL-HCCs is characterized polygonal neoplastic cells with abundant eosinophilic cytoplasm arranged in sheets, cords or trabeculae, divided by parallel sheets of fibrous tissue into lobules. About 20-60% FL-HCCs demonstrate a dense central scar[6], which may show calcification in 35%–68% cases[10]. FL-HCC often show predilection for left hepatic lobe and measure up to 5-20 cm[11]. They exhibit an increased propensity to metastasize to the lymph nodes (70%) and peritoneum[10, 12].

Extrahepatic extension of HCC (invasion of surrounding structures and/or metastases) is more common in non-cirrhotic patients with respect to their cirrhotic counterpart (20.5% vs. 6.5%)[3]. Some authors reported poor cancer differentiation and early portal tree invasion, in non-cirrhotic HCC when compared to their cirrhotic counterpart. This could represent squeal of delayed diagnosis or greater biological aggressiveness. Hemorrhage and necrosis is grossly visible in 10% of cases but microscopically can be present in one third of the cases[13].

Hepato-carcinogenesis and Cytogenetic Pathways

Development of HCC is multifactorial; a complex interplay of environmental factors, genetic factors and lifestyle factors lead to the development of HCC.

Stepwise carcinogenesis from regenerating nodule to dysplastic nodule to low grade followed by high grade carcinoma has been demonstrated in classical HCC developing in cirrhotic liver. Major molecular alterations involved in the development of HCC include aneuploidy and chromosomal aberrations (40%), activation of proto-oncogenes (β-catenin, ras-MAPK pathway), and inactivation of tumor suppressor genes (Rb, IGF2R, p53, and p16 INK4 mutations or deletions)[10]. However, NC-HCCs demonstrate de-novo carcinogenesis, and the molecular pathway involved is altogether different.

A selective mutation in codon 249 [AGG to AGT, leading to an arginine-to-serine substitution] of the p53 gene has been identified as a "hotspot" mutation for HCC, this mutation is strongly associated with exposure to aflatoxin B1 in combination with a high level of chronic hepatitis B virus infection in the population[14]. In hepatitis B virus infection a functional inactivation of p53 has been shown. The X protein of the virus (HBx) can interact with p53 and may also affect a variety of signal transduction pathways within the cell favoring cell survival and probably initiates hepatocarcinogenesis. NC-HCC shows lower rate of p53 mutation; however, it could be of wild variety and therefore demonstrates dismal prognosis. Moreover, a higher prevalence of β-catenin mutation, p14 inactivation and global gene methylation is seen in NC-HCCs[15]. Recently a suggestion of microsatellite instability which predicts deficiency in DNA mismatch repair system has been linked with NC-HCCs[16].

FL-HCC shows increased levels of Y654-β-catenin levels indicating increased receptor tyrosine kinase signaling. Majority (75%) of FL-HCCs show overexpression of anterior gradient-2 oncogene. However, FL-HCCs lack CTNNB or p53 mutations[10].

Predominant cytogenetic alteration and molecular pathway responsible for hepatocarcinogenesis significantly varies with the underlying etiology. For example, vinyl chloride induced HCC are linked with KRAS mutations, whereas HRAS mutations are associated with methylene chloride induced hepatomas[10].

Viral Hepatitis

Hepatitis B virus (HBV) is a DNA virus which can induce hepatic carcinogenesis independently of the liver cirrhosis[17]. HBV induced HCCs exhibit distinct set of genomic alterations. HBV genome integrates into the host cells and results in modification of several growth controlling genes through either host DNA microdeletions, through production of genotoxic viral product like HBX protein or affecting genes regulating cell signaling, proliferation, and viability. One of the major oncologic signaling pathways involved in hepatocarcinogenesis CTNNB1/β-catenin activation (reported in up to 50%) is frequently absent in HCCs induced by HBV[10].

Uniquely, patients with low viral load and high alpha fetoprotein levels demonstrate over-expression of insulin-like growth factor–2 (IGF2) and AXIN1 mutations. On the other hand, patients with high viral load demonstrate PIK3CA (the gene encoding phosphatidylinositol 3–kinase) mutations and p53 inactivation[10]. It is noteworthy, that overexpression of IGF2 and PIK3CA mutations are linked with activation of AKT pathway, which postulated as a major pathway to elicit HBV induced carcinogenesis[18]. Therefore, accumulation of mutations in basal core promoter and high viral load titers (>104-5 copies/ml) are independent risk factors in NC-HCC[19, 20].

Hepatitis C virus (HCV) is a RNA virus and is thought to have a lower direct oncogenic potential when compared to HBV, the main mechanism leading to HCC development is in a background of cirrhosis[21]. However, several HCV gene products (core, NS3, NS4B and NS5A) have demonstrated transformation process in murine fibroblast culture[22], suggesting that HCV also has a direct hepatocarcinogenic potential[23]. Moreover, HCV induced increased level of hepatic transforming growth factor (TGF), β signaling to fibrogenesis, accelerating liver fibrosis are also implicated in pathogenesis of HCC. Approximately 46% hepatitis C–related HCCs exhibit CTNNB mutations[10].

Alcohol

The alcohol has been implicated with pathogenesis of HCC in cirrhotic livers. However, alcohol can play a contributory or synergistic role in the etiopathogenesis of HCC in non-cirrhotic liver, especially on the background chronic hepatitis. The risk of HCC significantly (two to four times) increases in patients with hepatitis (B or C) who consume alcohol[24, 25]. The postulated mechanism of etiopathogenesis may include oxidative stress, DNA methylation, decreased immune surveillance, and genetic susceptibility.

Genotoxic Substances

A wide variety of genotoxins can influence the development of HCC in the non-cirrhotic liver.

Aflatoxin: Aspergillus flavus can contaminate cereals, nuts, figs, spices and dried fruits. The Aflatoxin B1 produced by this species of Aspergillus is known to be associated with a selective mutation in codon 249 (AGG to AGT, leading to an arginine-to-serine substitution) in p53 gene[26], which is identified as a hotspot mutation for HCC. Concomitant exposure to HBV infection leads to sixty fold increased risk in the HCC development[27]. This has been particularly reported from African and Asian countries.

Chemical and industrial carcinogens such as nitrosamines, azo-dyes, aromatic amines, vinyl chloride, organic solvents, pesticides and arsenic have been implicated in hepatic carcinogenesis in patients living in highly industrialized areas.

Radioactive elements such as thorotrast is a potential risk factor for development of HCC, although less frequently than angiosarcoma and cholangiocarcinoma[28].

Tissue iron overload may act as a genotoxic co-carcinogen factor, as would suggest the mild parenchymal iron accumulation found in the non-neoplastic liver parenchyma of most patients with NC-HCC[29].

Inherited diseases:

Inherited metabolic and congenital diseases or syndromes such as hereditary hemochromatosis, porphyria, alpha 1 antitrypsin deficiency, hypercitrullinemia, Wilson’s disease, type 1 glycogen storage disease, Alagille’s syndrome or congenital hepatic fibrosis may predispose to develop NC-HCC[2].

The postulated hypothesis suggest that accumulating mutant proteins or aggregation of substance within the hepatocytes activate a number of stress responses at genetic and cellular level, which in turn, induces proliferation and tumor formation[30]. Hemochromatosis induces cellular proliferation and direct damage to DNA resulting in inactivation of tumor suppressor genes (p53), formation of reactive oxygen species and lipid peroxidation, and acceleration of fibrogenesis, which all together lead to the formation of NC-HCC.

Metabolic syndrome (Combination of dyslipidemia, type 2 diabetes mellitus, hypertension, and obesity) is an important and emerging risk factor for HCC. The hypothesized carcinogens include insulin, lipid peroxidation, and oxidative stress induced by free radicals. Unopposed and persistent action of these carcinogens provokes cellular proliferation, activation of hepatic progenitor cells, and stimulates p53 mutations and epigenetic aberrations[31, 32].

Miscellaneous factors:

Hepatic adenoma: Overall, the risk of HCC development in hepatocellular adenoma is about 5-10%. In decreasing order of frequency, hepatic adenomas can be subdivided into three types, inflammatory, HNF-1alpha mutant adenoma and beta catenin mutant adenoma. The beta catenin mutant adenoma is more prone for malignant transformation to HCC[33]. Monoclonal mutations of both oncogenes and oncosuppressor genes leading to the mutation of β-catenin have been linked with development of HCC from adenoma.

Sex hormones: Anabolic C17-alkylated androgenic steroids and contraceptive steroids have been implicated as initiators or promoters of hepatic carcinogenesis, particularly after long term abuse[34].

Hepatic vascular pathology: Budd-chiari syndrome, nodular regenerative hyperplasia and hepatoportal sclerosis have been implicated as risk factors for HCC in the absence of cirrhosis[5, 35]. A quick reference of variegated etiological factors associated with NC-HCC has been described in box-1.

Diagnosis

Role of Serum Alpha Fetoprotein

Serum alpha-feto-protein (AFP) exceeding 20 ng/dl is seen in about 31-67% of non-cirrhotic HCC as compared to 59-84% in cirrhotic HCCs. Serum AFP levels exceeding 400 ng/dl is considered diagnostic for HCC both in the presence or absence of cirrhosis[3]. The serum α-fetoprotein level can be normal in FL-HCC.

Cross sectional imaging

Cross sectional imaging commonly demonstrates a large solitary mass or less commonly a dominant mass with satellite lesions[36]. Multiple masses without a dominant lesion are rare. The size of the mass can range from 2-23 cm (average size 10-12 cm). The right lobe appears to be commonly involved when compared to the left lobe with the exception of FL-HCC, which is commoner in left lobe.

Calcifications (peripheral or central), necrosis, hemorrhage or micro or macroscopic fatty metamorphosis is not uncommon. Occasionally, a focal intrahepatic biliary dilation could be seen, which might be related to mass effect rather than the ductal invasion. Tumor thrombus can be seen in portal or hepatic veins but less common (15%)[36]. An associated upper abdominal lymphadenopathy can be seen in up to 21% of the cases[8].

Computed Tomography

On unenhanced CT, the mass tends to be hypodense when compared to the surrounding liver parenchyma. Calcifications or hemorrhage in the tumor can appear as areas of hyperattenuation. On contrast enhanced CT the tumor demonstrate late arterial phase hyperenhancement and on portal venous phase the mass tends to be iso to hypodense with washout on equilibrium phase when compared to the surrounding liver parenchyma. Enhancing pseudocapsule can be seen on equilibrium phase.

FL-HCC is low-attenuating compared with the surrounding liver on non-contrast CT and may show intra-tumoral calcification in 68% cases[6]. On dynamic contrast-enhanced CT, it may show predominant heterogeneous enhancement, presence of a central scar (20-60%), and a pseudocapsule (35%)[37]. The central scar does not enhance in the equilibrium phase.

Magnetic Resonance Imaging

MRI is a very useful imaging modality in characterizing the focal liver lesions both in presence or absence of cirrhosis by virtue of its better soft tissue resolution. HCCs could be iso-hypo (most often) or hyperintense to the parenchyma on unenhanced T1 images. Presence of hemorrhage, fat, glycogen, high protein or copper in the lesion can result in T1 hyperintensity[38]. Fat is seen in approximately 10% of HCC, which is a sign of better prognosis [39]. Interestingly internal fat deposition in HCC is frequently (36%) seen in well-differentiated HCCs[38].

Comparisons of in- and opposed-phase images help identify the microscopic fat within the HCC. Areas of HCC containing microscopic fat are low signal intensity on opposed-phase images as compared to in-phase images. Low signal intensity in liver parenchyma on in-phase imaging suggests iron deposition which can be seen in cases of hemochromatosis.

On T2 weighted fast spin echo images the HCC demonstrates increased or intermediate signal intensity but the well-differentiated HCC can be iso to hypointense as compared to the surrounding normal liver parenchyma. Signal intensity of the HCC on T2 weighted images appears to correlate with the grade of malignancy; higher the intensity on T2W images, higher the grade HCC will show.

HCC can show restricted diffusion on diffusion weighted imaging with higher b-value, and also demonstrate low ADC values.

A central scar has been described in up to 50% NC-HCCs[36] and which may pose diagnostic difficulty; presence of central scar has also been described in fibrolamellar HCC or FNH .

Fat saturated post gadolinium T1W images can show hyperenhancement on the arterial phase imaging due to its predominant blood supply from the hepatic arterial feeders. The HCC tends to be iso to hypo intense on portal venous phase and show washout on the equilibrium phase. The surrounding fibrous capsule (pseudocapsule) is seen in approximately 80% of the cases, and is more conspicuous in this equilibrium phase. NC-HCC can invade veins lower in 15% cases[36].

Fibrolamellar HCC (FL-HCC) shows low signal intense on T1-weighted images, increased signal intensity on T2-weighted and heterogeneous enhancement on post-gadolinium images relative to surrounding liver parenchyma. However, the central scar shows hypointensity on T2W images. It is noteworthy, that FL-HCC with central necrosis or increased vascularity could demonstrate T2W hyperintense central scar[11]. The central scar does not show enhancement in equilibrium phase.

Differential diagnosis:

Hepatocellular adenoma:

Hepatocellular adenomas (HCA) commonly occur in women in the reproductive age group (M:F of 1:10). An increased incidence has been shown in patients on steroid therapy (i.e., estrogen or androgen containing steroids) and also in the setting of type I glycogen storage disorder. Up to 75% of adenomas occur in right lobe of liver.

Cross sectional imaging demonstrate variegated appearance of the tumor due to the presence of fat, necrosis or hemorrhage. The tumor tends to be hypoattenuating on unenhanced CT images, however, in the setting of diffuse fatty liver they tumor may appear hyperattenuating when compared to the adjacent liver parenchyma. Post contrast images demonstrate arterial hyperenhancement and variable washout on portal venous and equilibrium phase. MR promptly identifies presence of fat and hemorrhage.

Focal nodular hyperplasia:

Focal nodular hyperplasia (FNH) is second most common benign tumor and commonly occur in women in the reproductive age group (M:F of 1:8). Usually (75-80%) solitary, but can be multiple in 20-25% cases. FNH may co-exist with hemangioma in 20% of cases and hepatocellular adenoma in 4% of cases. They do not show hemorrhage or malignant transformation. FNHs are often characterized by a central scar and radiating fibrous cords that contain dystrophic vessels and reactive ductules.

On US, the FNHs are isoechoic to the liver and may show a central vascular scar. On cross sectional imaging the FNH is usually isoattenuating (or isointense) to the surrounding liver parenchyma on unenhanced CT or T1W images. However, there can be a reversal in imaging appearance in the presence of diffuse steatosis. The central scar is typically hyperintense on T2 weighted images. Post contrast imaging demonstrates homogeneous arterial phase hyperenhancement except for the scar. On portal venous and equilibrium phase the FNH becomes iso to the surrounding liver parenchyma and the central scar shows enhancement. The T1W/T2W intensity of the tumor and central scar (T2W intensity and the enhancement pattern) may differentiate FNHs from HCCs. However, Gd-BOPTA or gadoxetate disodium imaging can play a crucial role in diagnosis especially when scar is absent; FNHs demonstrate contrast retention in the hepatobiliary phase, whereas HCC shows washout.

Treatment and Prognosis

Surgical resection is the treatment of choice for NC-HCCs. Relatively preserved liver function despite a large tumor size offers an opportunity to perform larger resections, without significant perioperative mortality (0-6%) or morbidity (8-40%).

The 5-year overall survival after surgical resection of NC-HCC is much higher (44-58%) than the similar group with an underlying cirrhosis (23-48%). Recurrences after resection are not uncommon and can be seen in up to 27% -73% cases. Recurrences are mostly seen in the first two post-operative years and a stringent follow-up is recommended in this duration. About 11% to 39% of recurrences are treatable with a second hepatectomy. However, the treatment strategy for recurrent disease is indeed controversial; repeat hepatectomy may provide 5-year survival of up to 50%, but is usually associated with high incidence of re-recurrence[40]. Second and third hepatectomy for recurrent HCC may be equally safe and effective as the primary resection and may enable better results compared to the strategy of no repeat resection.

There is currently no strong evidence supporting adjuvant therapy to reduce the risk of recurrence after curative therapy. Adjuvant systemic chemotherapy with epirubicin, cisplatin and 5-fluorouracil or capecitabine regimens are well tolerated but the combination of both did not reveal a benefit on patient’s long term outcome[41, 42].

Sorafinib (Nexavar) is an oral multikinase inhibitor with activity against raf-kinase, VEGF receptor-2/3 (VEGFR-2/3) and platelet derived growth factor receptor beta (PDGFR-β) tyrosine kinases, thereby blocking cell proliferation and neoangiogenesis[43]. Sorafinib could be beneficial in the treatment of an unresectable HCC or improve the prognosis of the patients who undergo hepatic resection for NC-HCCs, and has been approved by FDA.

FL-HCCs demonstrate low number of cytogenetic aberrations and fewer chromosomal abnormalities and therefore less aggressive and show a better outcome than conventional HCC. Again, like other NC-HCC, surgical resection remains the mainstay of the treatment and the 5-year survival rate of is even better than NC-HCC ranging from 37% to 76% after complete surgical resection. FL-HCC demonstrates high levels of Y654-β-catenin levels or increased receptor tyrosine kinase signaling. This makes them highly susceptible to receptor tyrosine kinase targeting; therefore Sorafenib may have a strong therapeutic effect on FL-HCCs.

Orthotropic liver transplantation is reserved for patients with post-resection tumor recurrence in the liver.

Conclusion

HCCs developing in non-cirrhotic patients have distinct etiological, cytogenetical, histopathological and clinical features. Despite the larger tumor burden at the time of diagnosis they have a better overall and disease free survival. Knowledge of clinical and imaging features of this entity and other diagnostic considerations in non-cirrhotic liver is essential for improved patient care