Focal nodular hyperplasia--a review of myths and truths

Pedunculated Focal Nodular Hyperplasia: When in Doubt, Should We Cut It Out?

Focal nodular hyperplasia (FNH) is the second most common benign hepatic tumor and can rarely present as an exophytic solitary mass attached to the liver by a stalk. Most FNH cases are usually detected as incidental findings during surgery, imaging or physical examination and have a high female predominance. However, the pedunculated forms of FNH are particularly rare and commonly associated with severe complications and diagnostic challenges. Hence, our study aims to provide a comprehensive summary of the available data on the pedunculated FNH cases among adults and children. Furthermore, we will highlight the role of different therapeutic options in treating this clinical entity. The use of imaging techniques is considered a significant addition to the diagnostic toolbox. Regarding the optimal treatment strategy, the main indications for surgery were the presence of symptoms, diagnostic uncertainty and increased risk of complications, based on the current literature. Herein, we also propose a management algorithm for patients with suspected FNH lesions. Therefore, a high index of suspicion and awareness of this pathology and its life-threatening complications, as an uncommon etiology of acute abdomen, is of utmost importance in order to achieve better clinical outcomes.

Laparoscopic resection for pedunculated focal nodular hyperplasia of the liver during pregnancy

Focal nodular hyperplasia (FNH) is the second most common intrahepatic benign mass lesion; however, extremely rarely, FNH grows in an exophytic manner. It is unclear whether pedunculated FNH can be managed in the same way as intrahepatic FNH. A 35-year-old female presented with right upper quadrant pain, and dynamic enhanced computed tomography revealed an exophytic hyperdense mass lesion originating from the liver, suggesting a pedunculated FNH. Shortly thereafter, she conceived. Since there was a history of acute abdomen, as well as the possibility of torsion of the mass or sudden massive bleeding during pregnancy, laparoscopic resection was performed at 17 weeks of gestation. Her postoperative and pregnancy course was uneventful, and she delivered a baby by cesarean section at 41 weeks of gestation. Our case suggests that pedunculated FNH, unlike typical intrahepatic FNH, may be better managed by laparoscopic surgery during pregnancy, resulting in favorable maternal and fetal outcomes.

Imaging strategy for focal nodular hyperplasia in children: long-term experience from two specialist European centres

BACKGROUND

Focal nodular hyperplasia (FNH) in children is a rare but benign tumour, which must be differentiated from malignant entities to avoid unnecessary treatment, leading to potential morbidity.

OBJECTIVES

To provide data on imaging findings of these lesions with a suggested algorithm for diagnosis, sampling and follow-up.

MATERIALS AND METHODS

This retrospective review evaluated imaging of all patients diagnosed with FNH in two tertiary referral centres in Europe between 1975 and 2018.

RESULTS

One hundred and four patients with 137 tumours were reviewed. The mean age at presentation was 8.2 years. The median tumour size was 5 cm (range: 0.3-29 cm). Multiple lesions were seen in 16.3% of patients. The male-to-female ratio was 1:2.

CONCLUSION

FNH with typical features on imaging can be safely followed up once the diagnosis has been established. The use of contrast-enhanced ultrasound and magnetic resonance imaging allows accurate characterisation in most cases. Histological sampling is only advised when there is diagnostic doubt. Atypical arterial enhancement of FNH should prompt the search for a congenital portosystemic shunt.

Multi-omics characterization reveals the pathogenesis of liver focal nodular hyperplasia

The molecular landscape and pathogenesis of focal nodular hyperplasia (FNH) have yet to be elucidated. We performed multi-omics approaches on FNH and paired normal liver tissues from 22 patients, followed by multi-level bioinformatic analyses and experimental validations. Generally, FNH had low mutation burden with low variant allele frequencies, and the mutation frequency significantly correlated with proliferation rate. Although no recurrently deleterious genomic events were found, some putative tumor suppressors or oncogenes were involved. Mutational signatures indicated potential impaired mismatch function and possible poison contact. Integrated analyses unveiled a group of FNH specific endothelial cells that uniquely expressed SOST and probably had strong interaction with fibroblasts through PDGFB/PDGFRB pathway to promote fibrosis. Notably, in one atypical FNH (patient No.11) with pronounced copy number variations, we observed a unique immune module. Most FNH are benign, but molecularly atypical FNH still exist; endothelial cell derived PDGFB probably promotes the fibrogenic process in FNH.

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FNHs are genetically stable, but high mutation cases exist

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FNHs have unique transcriptomic modules, and they alter in atypical FNH

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FNH has a unique type of SOST-expressing endothelial cells that may promote fibrosis

Genomic analysis of focal nodular hyperplasia with associated hepatocellular carcinoma unveils its malignant potential: a case report

Background

Focal nodular hyperplasia (FNH) is typically considered a benign tumor of the liver without malignant potential. The co-occurrence of FNH and hepatocellular carcinoma (HCC) has been reported in rare cases. In this study we sought to investigate the clonal relationship between these lesions in a patient with FNH-HCC co-occurrence.

Methods

A 74-year-old female patient underwent liver tumor resection. The resected nodule was subjected to histologic analyses using hematoxylin and eosin stain and immunohistochemistry. DNA extracted from microdissected FNH and HCC regions was subjected to whole exome sequencing. Clonality analysis were performed using PyClone.

Results

Histologic analysis reveals that the nodule consists of an FNH and two adjoining HCC components with distinct histopathological features. Immunophenotypic characterization and genomic analyses suggest that the FNH is clonally related to the HCC components, and is composed of multiple clones at diagnosis, that are likely to have progressed to HCC through clonal selection and/or the acquisition of additional genetic events.

Conclusion

To the best of our knowledge, our work is the first study showing a clonal relationship between FNH and HCC. We show that FNH may possess the capability to undergo malignant transformation and to progress to HCC in very rare cases.

A case of inferior right hepatic vein-right hepatic vein bypass with interrupted inferior vena cava compressed by focal nodular hyperplasia in caudate lobe

Focal nodular hyperplasia (FNH) is a relatively common benign liver tumor with rare indications to surgery. Budd-Chiari syndrome is a rare condition caused by interrupted hepatic venous outflow in the hepatic veins and inferior vena cava (IVC). A 42-year-old woman was referred to our department with a hepatic tumor. Patient's chief complaint was leg edema. Because of this symptom, it was difficult for the patient to stand for more than 20 min in the evening. Computed tomography (CT) showed a hypervascular mass compressing IVC in the caudate lobe of the liver. Fine needle aspiration was performed, and preoperative diagnosis was focal nodular hyperplasia (FNH). Hepatic resection of the right caudate lobe was performed. Postoperative histological examination revealed that the tumor was FNH. After surgery, the patient's leg edema disappeared, and postoperative CT revealed that severe IVC stenosis was improved. Although there have been several reports of giant FNH causing Budd-Chiari syndrome, this case shows the stenosis of IVC below the root of hepatic veins causing Budd-Chiari-like syndrome without portal hypertension. The location of the tumor considerably attributed to the congestion of venous flow in IVC causing various symptoms and intrahepatic inferior right hepatic vein-right hepatic vein bypass. The surgical indication of FNH is limited in most cases; however, the current report alerts that the location of FNH should be taken into account when monitoring it.

MicroRNA Expression in Focal Nodular Hyperplasia in Comparison with Cirrhosis and Hepatocellular Carcinoma

The liver disease focal nodular hyperplasia (FNH) has several histological features that resemble hepatic cirrhosis. Since cirrhosis may develop further into hepatocellular carcinoma (HCC) contrary to FNH, the aim of the present study was to identify microRNAs (miRNA), which, by their altered expression levels, may be associated with the benign, tumor-like nature of FNH. Altogether 106 surgically removed formalin-fixed paraffin-embedded liver samples were selected, including 22 FNH, 45 cirrhosis, 24 HCC and 15 normal liver tissues. Etiology of the cases of cirrhosis and HCC includes hepatitis C and alcoholism and the HCC cases developed in cirrhotic livers. Relative expression levels of 14 miRNAs were determined using TaqMan MicroRNA Assays. In comparison to normal liver, the levels of miR-34a and miR-224 were elevated not only in FNH but also in cirrhosis and HCC, while the expression of miR-17-5p, miR-18a and miR-210 was decreased in FNH. Further, the levels of miR-21 and miR-222 were increased in cirrhosis and HCC but were decreased in FNH and the expression of miR-17-5p, miR-18a, miR-195 and miR-210 was decreased in FNH as compared with cirrhosis and/or HCC. In conclusion, the elevation of miR-34a and miR-224 may be associated with both benign and malignant proliferative processes, nevertheless the increased expression of oncomiRs miR-21 and miR-222 in cirrhosis and HCC but not in FNH may be related to malignant processes of the liver. The decreased levels of miR-18a, miR-195 and miR-210 may further differentiate FNH from cirrhosis, reflecting the different pathogenesis of these two entities contrary to some histologically similar features.

What is Changing in Indications and Treatment of Focal Nodular Hyperplasia of the Liver. Is There Any Place for Surgery?

Focal nodular hyperplasia (FNH) is a common benign liver tumor, which occurs in the vast majority of the cases in young women. FNH represents a polyclonal lesion characterized by local vascular abnormalities and is a truly benign lesion without any potential for malignant transformation. A retrospective single institution analysis of 227 FNH patients, treated from 1990 to 2016 and a review of studies reporting surgical therapy of overall 293 patients with FNH was performed. Indications for resection with a focus on diagnostic workup, patient selection, surgical mode and operative mortality and morbidity have been analysed. Ninety three patients underwent elective hepatectomy and 134 patients observation alone, where median follow-up was 107 months. Postoperative complications were recorded in 14 patients, 92% of patients reported an improvement with respect to their symptoms. Overall among 293 patients underwent surgery in the series, included to this review, there was a morbidity of 13%, where median follow-up was 53 months. Systematic follow-up remains the gold standard in asymptomatic patients with FNH. However elective surgery should be considered in symptomatic patients, in those with marked enlargement and in case of uncertainty of diagnosis. Surgery for FNH is a safe procedure with low morbidity and very good long term results as far as quality of life after surgery is concerned and surely an integral part of the modern management of FNH.

Tissue sublimation follow transarterial embolization of a follicular nodular hyperplasia of the liver-report of a case

Background

Follicular nodular hyperplasia (FNH) is a common benign liver tumor for which conservative management is indicated. Surgical or interventional management is indicated in symptomatic cases. Transarterial embolization (TAE) has been extensively used to manage unresectable liver tumors. Sublimation describes a change of physical state from solid to gas. Hepatic tissue sublimation following TAE has so far not been reported in medical literature.

Case presentation

A 30 year - old male patient presenting with pain to the upper abdomen due to a large FNH was managed with TAE. Routine radiographic control on post-intervention day one was within normal limits. Imaging due to right upper quadrant pain with fever and elevated inflammatory markers and liver enzymes on day two after TAE revealed a marked reduction of the FNH accompanied by the presence of a large volume of gas collection without signs of abscess formation. This change of state from solid to gas without sign of abscess formation within 2 days after TAE was described as hepatic tissue sublimation. The patient was managed conservatively and discharge 12 days after TAE.

Conclusion

Tissue sublimation has hardly been reported in medical literature. This to the best of our knowledge is the first documented case of hepatic tissue sublimation following TAE.

Typical and atypical benign liver lesions: A review

Focal liver lesions are routinely encountered by clinical radiologists and represent a wide spectrum of pathology. Majority of these lesions are likely to be benign in nature, especially in the absence of chronic liver disease or primary cancer. A radiologist must be aware of common and uncommon imaging features of benign lesions across the various imaging modalities. This review discusses pathognomonic imaging features of common benign focal liver lesions seen on ultrasound, computed tomography and magnetic resonance, and adds to existing knowledge with the recent updates to have emerged in this area.

Sclerosing Angiomatoid Nodular Transformation of the spleen, focal nodular hyperplasia and hemangioma of the liver: A tale of three lesions

Sclerosing Angiomatoid Nodular Transformation (SANT) of the spleen is a benign vascular lesion with peculiar histological features. The pathogenesis of SANT is still largely unknown and variable etiologies have been proposed, including autoimmune, inflammatory, and/or vascular disorders. The present report describes a unique case of splenic SANT, associated with focal nodular hyperplasia and a sclerosing hemangioma of the liver. The clinic-pathological features of such an unusual case are thoroughly illustrated. Its possible pathogenic mechanisms are also briefly addressed.

Insulinoma with focal hepatic lesions: malignant insulinoma?

Insulinoma is a rare tumour that is malignant in only 10% of cases. We report a case of insulinoma in a 59-year-old woman, associated with focal liver lesions, which raised the suspicion of malignancy of a pancreatic tumour. Enucleation of the insulinoma was performed with wedge resection of one hepatic nodule. Pathological examination indicated that the pancreatic tumour was compatible with insulinoma whereas the hepatic lesion was related to focal nodular hyperplasia. This clinical case highlights the need for histopathological proof of malignancy before selecting therapeutic strategies for insulinomas.

The value of liver resection for focal nodular hyperplasia: resection yes or no?

Background

Focal nodular hyperplasia (FNH) are benign lesions in the liver. Although liver resection is generally not indicated in these patients, rare indications for surgical approaches indeed exist. We here report on our single-center experience with patients undergoing liver resection for FNH, focussing on preoperative diagnostic algorithms and quality of life (QoL) after surgery.

Methods

Medical records of 100 consecutive patients undergoing liver resection for FNH between 1992 and 2012 were retrospectively analyzed with regard to diagnostic pathways and indications for surgery. Quality of life (QoL) before and after surgery was evaluated using validated assessment tools. Student’s t test, one-way ANOVA, χ², and binary logistic regression analyses such as Wilcoxon–Mann–Whitney test were used, as indicated.

Results

A combination of at least two preoperative diagnostic imaging approaches was applied in 99 cases, of which 70 patients were subjected to further imaging or tumor biopsy. In most patients, there was more than one indication for liver resection, including tumor-associated symptoms with abdominal discomfort (n = 46, 40.7 %), balance of risk for malignancy/history of cancer (n = 54, 47.8 %/n = 18; 33.3 %), tumor enlargement/jaundice of vascular and biliary structures (n = 13, 11.5 %), such as incidental findings during elective operation (n = 1, 0.9 %). Postoperative morbidity was 19 %, with serious complications (>grade 2, Clavien–Dindo classification) being evident in 8 %. Perioperative mortality was 0 %. Liver resection was associated with a significant overall improvement in general health (very good–excellent: preoperatively 47.4 % vs. postoperatively 68.1 %; p = 0.015).

Conclusions

Liver resection remains a valuable therapeutic option in the treatment of either symptomatic FNH or if malignancy cannot finally be ruled out. If clinically indicated, liver resection for FNH represents a safe approach and may lead to significant improvements of QoL especially in symptomatic patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s40001-015-0181-x) contains supplementary material, which is available to authorized users.

Loss of DNA methylation at imprinted loci is a frequent event in hepatocellular carcinoma and identifies patients with shortened survival

Background

Aberrant DNA methylation at imprinted loci is an important molecular mechanism contributing to several developmental and pathological disorders including cancer. However, knowledge about imprinting defects due to DNA methylation changes is relatively limited in hepatocellular carcinoma (HCC), the third leading cause of cancer death worldwide. Therefore, comprehensive quantitative DNA methylation analysis at imprinted loci showing ~50 % methylation in healthy liver tissues was performed in primary HCC specimens and the peritumoural liver tissues.

Results

We found frequent and extensive DNA methylation aberrations at many imprinted loci in HCC. Unsupervised cluster analysis of DNA methylation patterns at imprinted loci revealed subgroups of HCCs with moderate and severe loss of methylation. Hypomethylation at imprinted loci correlated significantly with poor overall survival (log-rank test, p = 0.02). Demethylation at imprinted loci was accompanied by loss of methylation at LINE-1, a commonly used marker for global DNA methylation levels (p < 0.001). In addition, we found that loss of methylation at imprinted loci correlated with the presence of a CTNNB1 mutation (Fisher’s exact test p = 0.03). Re-analysis of publically available genome-wide methylation data sets confirmed our findings. The analysis of benign liver tumours (hepatocellular adenoma (HCA) and focal nodular hyperplasia (FNH)), the corresponding adjacent liver tissues, and healthy liver tissues showed that aberrant DNA methylation at imprinted loci is specific for HCC.

Conclusions

Our analyses demonstrate frequent and widespread DNA methylation aberrations at imprinted loci in human HCC and identified a hypomethylated subgroup of patients with shorter overall survival.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-015-0145-6) contains supplementary material, which is available to authorized users.

Focal liver lesions: Practical magnetic resonance imaging approach

With the widespread of cross-sectional imaging, a growth of incidentally detected focal liver lesions (FLL) has been observed. A reliable detection and characterization of FLL is critical for optimal patient management. Maximizing accuracy of imaging in the context of FLL is paramount in avoiding unnecessary biopsies, which may result in post-procedural complications. A tremendous development of new imaging techniques has taken place during these last years. Nowadays, Magnetic resonance imaging (MRI) plays a key role in management of liver lesions, using a radiation-free technique and a safe contrast agent profile. MRI plays a key role in the non-invasive correct characterization of FLL. MRI is capable of providing comprehensive and highly accurate diagnostic information, with the additional advantage of lack of harmful ionizing radiation. These properties make MRI the mainstay for the noninvasive evaluation of focal liver lesions. In this paper we review the state-of-the-art MRI liver protocol, briefly discussing different sequence types, the unique characteristics of imaging non-cooperative patients and discuss the role of hepatocyte-specific contrast agents. A review of the imaging features of the most common benign and malignant FLL is presented, supplemented by a schematic representation of a simplistic practical approach on MRI.

Oestrogen hormone receptors in focal nodular hyperplasia

BACKGROUND

The role of hormones in focal nodular hyperplasia (FNH) has been investigated with conflicting results.

OBJECTIVE

The aim of this study was to evaluate oestrogen and progesterone receptor immunohistochemical expression in FNH and surrounding normal liver (control material).

METHODS

Biopsy materials from FNH and control tissue were investigated using an immunostainer. Receptor expression was graded as the proportion score (percentage of nuclear staining) and oestrogen receptor intensity score.

RESULTS

Study material included tissue from 11 resected FNH lesions and two core biopsies in 13 patients (two male). Twelve samples showed oestrogen receptor expression. The percentage of nuclear oestrogen receptor staining was <33% in eight FNH biopsies, 34-66% in two FNH biopsies, and >67% in both core biopsies. The better staining in core biopsies relates to limitations of the staining technique imposed by the fibrous nature of larger resected FNH. Control samples from surrounding tissue were available for nine of the resected specimens and all showed oestrogen receptor expression. Progesterone receptor expression was negligible in FNH and control samples.

CONCLUSIONS

By contrast with previous studies, the majority of FNH and surrounding liver in this cohort demonstrated oestrogen receptor nuclear staining. The implications of this for continued oral contraceptive use in women of reproductive age with FNH remain uncertain given the lack of consistent reported growth response to oestrogen stimulation or withdrawal.

MR characterization of focal liver lesions: pearls and pitfalls

Magnetic resonance (MR) can characterize specific tissue subtypes, thus facilitating focal liver lesion diagnosis. Focal liver lesions that are isointense to hyperintense to liver on T1-weighted images are usually hepatocellular in origin. Chemical shift imaging can narrow the differential diagnosis by detecting the presence of lipid or iron. T2 and heavily T2-weigthed fast spin echo imaging can differentiate solid from nonsolid focal liver lesions. The authors illustrate these MR imaging pearls and the uncommon exceptions (pitfalls). The authors hope that you will find this less traditional contribution to the Magnetic Resonance Clinics of North America helpful in clinical practice.

Calcified telangiectatic hyperplastic nodule associated with vascular malformation in a child: a case report

This is a case report of an asymptomatic 4-year-old girl who was found to have a nodule at the lateral left lobe of the liver. She underwent transabdominal liver ultrasound and abdominal MRI that showed calcification and intense arterial enhancement but they failed to clearly exclude malignancy. The patient underwent an unremarkable laparoscopic wedge liver resection of the lesion because of its location and size. Pathological examination showed features compatible with a benign telangiectatic hyperplastic nodule with vascular malformation and calcification. CD34 immunostained the proliferative vascular lining cells while CK7 and CK19 highlighted the normal bile ducts present within the lesion. The diagnosis of a telangiectatic hyperplastic nodule associated with vascular malformation has been scarcely reported in children and our case shows for the first time that it can also present with calcifications.

Concordant hypermethylation of intergenic microRNA genes in human hepatocellular carcinoma as new diagnostic and prognostic marker

Epigenetic inactivation by aberrant DNA methylation has been reported for many microRNA genes in various human malignancies. However, relatively little is known about microRNA gene methylation in hepatocellular carcinoma (HCC). Therefore, a systematic screen for identification of aberrantly hypermethylated microRNA genes in HCC was initiated. The methylation status of 39 intergenic CpG island associated microRNA genes was analyzed in HCC cell lines (n = 7), immortalized hepatocytes (n = 2) and normal liver samples (n = 5). Subsequently, 13 differentially methylated microRNA genes were analyzed in primary human HCC samples (n = 40), benign liver tumors (n = 15) and the adjacent liver tissues employing pyrosequencing. Expression of microRNA genes was measured using quantitative real-time polymerase chain reaction (RT-PCR). In addition, DNA methylation and expression of microRNA genes were measured after DNMT1 knockdown or DNMT inhibition. Aberrant hypermethylation and concomitant reduction in expression of intergenic microRNA genes is a frequent event in human HCC: hsa-mir-9-2 (23%), hsa-mir-9-3 (50 %), hsa-mir-124-1 (20%), hsa-mir-124-2 (13%), hsa-mir-124-3 (43%), hsa-mir-129-2 (58%), hsa-mir-596 (28%) and hsa-mir-1247 (38%). Altogether, it affects 90% of the HCC specimens under study. MicroRNA gene methylation is not found in hepatocellular adenoma (n = 10) and focal nodular hyperplasia (n = 5). DNMT1 knockdown or DNMT inhibition reduced microRNA gene methylation and stimulated expression. In primary human HCC specimens hypermethylation and expression of microRNA genes showed an inverse correlation. Concordant hypermethylation of three or more microRNA genes is a highly specific marker for the detection of HCC and for poor prognosis.

Gastric outlet obstruction caused by focal nodular hyperplasia of the liver: A case report and literature review

INTRODUCTION

Here, we present a case of gastric outlet obstruction due to focal nodular hyperplasia of the liver.

PRESENTATION OF CASE

A 23-year-old female presented to our emergency clinic with nausea, vomiting, and abdominal pain. Endoscopy showed that the prepyloric region of the stomach was externally compressed by a lesion. Computed tomography and magnetic resonance imaging revealed a 70mm solid mass originating from the liver, extending caudally in an exophytic manner, and compressing the stomach. Laparotomy revealed an irregular and exophytic mass originating from the liver, which caused gastric outlet obstruction. The mass was resected with a 10mm safety margin. The histopathology report of the mass returned as focal nodular hyperplasia.

DISCUSSION

Gastric outlet obstruction is a clinical syndrome characterized by abdominal pain, nausea, and postprandial vomiting. This clinical condition frequently develops as a result of peptic ulcer disease, pyloric stenosis, and obstruction of pylorus by foreign bodies including phytobezoars, congenital duodenal webs, malignant disorders, and various lesions externally compressing the stomach. Gastric outlet obstruction due to hepatic lesions is extremely rare; few cases have been reported.

CONCLUSION

This is the first reported case of gastric outlet obstruction that developed due to focal nodular hyperplasia of the liver.

Loss of imprinting and allelic switching at the DLK1-MEG3 locus in human hepatocellular carcinoma

Deregulation of imprinted genes is an important molecular mechanism contributing to the development of cancer in humans. However, knowledge about imprinting defects in human hepatocellular carcinoma (HCC), the third leading cause of cancer mortality worldwide, is still limited. Therefore, a systematic meta-analysis of the expression of 223 imprinted loci in human HCC was initiated. This screen revealed that the DLK1-MEG3 locus is frequently deregulated in HCC. Deregulation of DLK1 and MEG3 expression accompanied by extensive aberrations in DNA methylation could be confirmed experimentally in an independent series of human HCC (n = 40) in more than 80% of cases. Loss of methylation at the DLK1-MEG3 locus correlates linearly with global loss of DNA methylation in HCC (r(2) = 0.63, p<0.0001). Inhibition of DNMT1 in HCC cells using siRNA led to a reduction in MEG3-DMR methylation and concomitant increase in MEG3 RNA expression. Allele-specific expression analysis identified loss of imprinting in 10 out of 31 informative samples (32%), rendering it one of the most frequent molecular defects in human HCC. In 2 cases unequivocal gain of bi-allelic expression accompanied by substantial loss of methylation at the IG-DMR could be demonstrated. In 8 cases the tumour cells displayed allelic switching by mono-allelic expression of the normally imprinted allele. Allelic switching was accompanied by gains or losses of DNA methylation primarily at IG-DMR1. Analysis of 10 hepatocellular adenomas (HCA) and 5 cases of focal nodular hyperplasia (FNH) confirmed that this epigenetic instability is specifically associated with the process of malignant transformation and not linked to increased proliferation per se. This widespread imprint instability in human HCC has to be considered in order to minimize unwanted side-effects of therapeutic approaches targeting the DNA methylation machinery. It might also serve in the future as predictive biomarker and for monitoring response to epigenetic therapy.