Genes Associated With Progression and Recurrence of Hepatocellular Carcinoma in Hepatitis C Patients Waiting and Undergoing Liver Transplantation: Preliminary Results

Transcriptome analysis creates a new era of precision medicine for managing recurrent hepatocellular carcinoma

The high incidence of hepatocellular carcinoma (HCC) recurrence negatively impacts outcomes of patients treated with curative intent despite advances in surgical techniques and other locoregional liver-targeting therapies. Over the past few decades, the emergence of transcriptome analysis tools, including real-time quantitative reverse transcription PCR, microarrays, and RNA sequencing, has not only largely contributed to our knowledge about the pathogenesis of recurrent HCC but also led to the development of outcome prediction models based on differentially expressed gene signatures. In recent years, the single-cell RNA sequencing technique has revolutionized our ability to study the complicated crosstalk between cancer cells and the immune environment, which may benefit further investigations on the role of different immune cells in HCC recurrence and the identification of potential therapeutic targets. In the present article, we summarized the major findings yielded with these transcriptome methods within the framework of a causal model consisting of three domains: primary cancer cells; carcinogenic stimuli; and tumor microenvironment. We provided a comprehensive review of the insights that transcriptome analyses have provided into diagnostics, surveillance, and treatment of HCC recurrence.

Transcriptional activation of PD-L1 by Sox2 contributes to the proliferation of hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC) is one of the most common and lethal malignancies in the world. Sox2 is a potential oncogene in the pathogenesis of HCC, however, the actual mechanisms of Sox2 functions in HCC has not emerged yet. In this study, we explored the expression, function and the relationship between Sox2 and PD-L1 in HCC. We found that both Sox2 and PD-L1 were expressed at a markedly higher level in HCC tissues in comparison to adjacent non-tumor tissues. Moreover, the expression levels of both genes were correlated with each other. Knockdown of Sox2 reduced the cell proliferation ability and induces apoptosis of HCC cells, suggesting the function of Sox2 in regulating both the cell proliferation and apoptosis. Noteworthy, the depletion of Sox2 also reduced the expression of PD-L1. Further analysis showed that there is a consensus Sox2 binding site in the promoter region of PD-L1. Through in vitro EMSA assay and in vivo chromatin immunoprecipitation assays, we demonstrated that Sox2 directly bound to the PD-L1 promoter through the consensus Sox2 motif. Further evidence by luciferase reporter assays revealed that Sox2 promoted the transcription activity of PD-L1 promoter region through the Sox2 motif. Collectively, our data provide a novel insight into the function and the interplay of Sox2 and PD-L1 in HCC.

KLHL21, a novel gene that contributes to the progression of hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) has very high prevalence and associated-mortality. However, targeted therapies that are currently used in clinical practice for HCC have certain limitations, in part because of the lack of reliable and clinically applicable biomarkers that can be used for diagnosis and prognosis assessments and for the surveillance of treatment effectiveness.

METHODS

Meta-analysis was used to analyze the integrated microarray data for global identification of a set of robust biomarkers for HCC. Quantitative RT-PCR (qRT-PCR) was performed to validate the expression levels of selected genes. Gene expression was inhibited by siRNA. CellTiter 96^® AQueous One Solution Cell Proliferation assays were used to determine cell proliferation, and Transwell assays were used to determine cell migration and invasion potential.

RESULTS

Meta-analysis of the expression data provided a gene expression signature from a total of 1525 patients with HCC, showing 1529 up-regulated genes and 478 down-regulated genes in cancer samples. The expression levels of genes having strong clinical significance were validated by qRT-PCR using primary HCC tissues and the paired adjacent noncancerous liver tissues. Up-regulation of VPS45, WIPI1, TTC1, IGBP1 and KLHL21 genes and down-regulation of FCGRT gene were confirmed in clinical HCC samples. KLHL21 was the most promising gene for potential use as a bioclinical marker in this analysis. Abrogating expression of it significantly inhibited cell proliferation, migration and invasion.

CONCLUSIONS

Our study suggests that KLHL21 is a potential target for therapeutic intervention. Our findings also provide novel candidate genes on a genome-wide scale, which may have significant impact on the design and execution of effective therapy of HCC patients.

Deleted in liver cancer-1 (DLC1): an emerging metastasis suppressor gene

While significant progress continues to be made in the early detection and therapeutic management of primary tumors, the incidence of metastatic disease remains the major cause of mortality. Accordingly, the development of novel effective therapies that can ameliorate dissemination and secondary tumor growth are a clinical priority. The identification of genetic and functional alterations in cancer cells that affect factors implicated in the metastatic process is critical for designing preventive and therapeutic strategies. Evidence implicating the protein deleted in liver cancer-1 (DLC1), a Rho GTPase activator, in metastasis has accumulated to a point where DLC1 may be considered as a metastasis suppressor gene. This review presents evidence supporting an anti-metastatic role for DLC1 in several human cancers and discusses the mechanisms contributing to its inhibitory effects. In addition, promising opportunities for therapeutic interventions based on DLC1 function and downstream pathways involved in the metastatic process are considered.

Multimodality therapy and liver transplantation for hepatocellular carcinoma: a 14-year prospective analysis of outcomes

BACKGROUND

Hepatocellular carcinoma is a major cause of death among patients with cirrhosis. A standardized approach of multimodality therapy with intent-to-treat by transplantation for all patients with hepatocellular carcinoma was instituted at our transplant center in 1997. Data were prospectively collected to evaluate the impact of multimodality therapy on posttransplant patient survival, tumor recurrence, and patient survival without transplantation.

METHODS

All patients with hepatocellular carcinoma were eligible for multimodality therapy. Multimodality therapy consisted of hepatic resection, radiofrequency ablation, transarterial chemoembolization, transarterial chemoinfusion, yttrium-90 microsphere radioembolization, and sorafenib.

RESULTS

Approximately 715 patients underwent multimodality therapy; 231 patients were included in the intent-to-treat with transplantation arm, and 484 patients were treated with multimodality therapy or palliative therapy because of contraindications for transplantation. A 60.2% transplantation rate was achieved in the intent-to-treat with transplantation arm. Posttransplant survivals at 1 and 5 years were 97.1% and 72.5%, respectively. Tumor recurrence rates at 1, 3, and 5 years were 2.4%, 6.2%, and 11.6%, respectively. Patients with contraindications to transplant had increased 1- and 5-year survival from diagnosis with multimodality therapy compared with those not treated (73.1% and 46.5% versus 15.5% and 4.4%, P<0.0001).

CONCLUSIONS

Using multimodality therapy before liver transplantation for hepatocellular carcinoma achieved low recurrence rates and posttransplant survival equivalent to patients with primary liver disease without hepatocellular carcinoma. Multimodality therapy may help identify patients with less active tumor biology and result in improved disease-free survival and organ utilization.

Liver Transplantation for Hepatocellular Carcinoma beyond Milan Criteria: Multidisciplinary Approach to Improve Outcome

The implementation of the Milan criteria (MC) in 1996 has dramatically improved prognosis after liver transplantation (LT) in patients with hepatocellular carcinoma (HCC). Liver transplantation has, thereby, become the standard therapy for patients with "early-stage" HCC on liver cirrhosis. The MC were consequently adopted by United Network of Organ Sharing (UNOS) and Eurotransplant for prioritization of patients with HCC. Recent advancements in the knowledge about tumor biology, radiographic imaging techniques, locoregional interventional treatments, and immunosuppressive medications have raised a critical discussion, if the MC might be too restrictive and unjustified keeping away many patients from potentially curative LT. Numerous transplant groups have, therefore, increasingly focussed on a stepwise expansion of selection criteria, mainly based on tumor macromorphology, such as size and number of HCC nodules. Against the background of a dramatic shortage of donor organs, however, simple expansion of tumor macromorphology may not be appropriate to create a safe extended criteria system. In contrast, rather the implementation of reliable prognostic parameters of tumor biology into selection process prior to LT is mandatory. Furthermore, a multidisciplinary approach of pre-, peri-, and posttransplant modulating of the tumor and/or the patient has to be established for improving prognosis in this special subset of patients.

Molecular Signatures of Recurrent Hepatocellular Carcinoma Secondary to Hepatitis C Virus following Liver Transplantation

Chronic hepatitis C virus (HCV) induced hepatocellular carcinoma (HCC) is a primary indication for liver transplantation (LT). In western countries, the estimated rate of HCC recurrence following LT is between 15% and 20% and is a major cause of mortality. Currently, there is no standard method to treat patients who are at high risk for HCC recurrence. The aim of this study was to investigate the molecular signatures underlying HCC recurrence that may lead to future studies on gene regulation contributing to new therapeutic options. Two groups of patients were selected, one including patients with HCV who developed HCC recurrence (HCC-R) ≤3 years from LT and the second group including patients with HCV who did not have recurrent HCC (HCC-NR). Microarray analysis containing more than 29,000 known genes was performed on formalin-fixed-paraffin-embedded (FFPE) liver tissue from explanted livers. Gene expression profiling revealed 194 differentially regulated genes between the two groups. These genes belonged to cellular networks including cell cycle G1/S checkpoint regulators, RAN signaling, chronic myeloid leukemia signaling, molecular mechanisms of cancer, FXR/RXR activation and hepatic cholestasis. A subset of molecular signatures associated with HCC recurrence was found. The expression levels of these genes were validated by quantitative PCR analysis.

Liver transplantation for hepatocellular carcinoma: a model including α-fetoprotein improves the performance of Milan criteria

BACKGROUND & AIMS

The aim of this study was to generate an improved prognostic model for predicting recurrence in liver transplant candidates with hepatocellular carcinoma (HCC).

METHODS

Predictors of recurrence were tested by a Cox model analysis in a training cohort of 537 patients transplanted for HCC. A prognostic score was developed and validated in a national cohort of 435 patients followed up prospectively.

RESULTS

α-Fetoprotein (AFP) independently predicted tumor recurrence and correlated with vascular invasion and differentiation. At a Cox score threshold of 0.7 (area under the receiver operating characteristic curve, 0.701; 95% confidence interval, 0.63-0.76; accuracy, 75.8%), a model combining log(10) AFP, tumor size, and number was highly predictive of tumor recurrence and death. By using a simplified version of the model, with untransformed AFP values, a cut-off value of 2 was identified. In the validation cohort, a score greater than 2 predicted a marked increase in 5-year risk of recurrence (50.6% ± 10.2% vs 8.8% ± 1.7%; P < .001) and decreased survival (47.5% ± 8.1% vs 67.8% ± 3.4%; P = .002) as compared with others. Among patients exceeding Milan criteria, a score of 2 or lower identified a subgroup of patients with AFP levels less than 100 ng/mL with a low 5-year risk of recurrence (14.4% ± 5.3% vs 47.6% ± 11.1%; P = .006). Among patients within Milan criteria, a score greater than 2 identified a subgroup of patients with AFP levels greater than 1000 ng/mL at high risk of recurrence (37.1% ± 8.9% vs 13.3% ± 2.0%; P < .001). Net reclassification improvement showed that predictability of the AFP model was superior to Milan criteria.

CONCLUSIONS

Prediction of tumor recurrence is improved significantly by a model that incorporates AFP. We propose the adoption of new selection criteria for HCC transplant candidates, taking into account AFP.

Molecular classification and clonal differentiation of hepatocellular carcinoma: the step forward for patient selection for liver transplantation

Liver transplantation is a successful treatment for hepatocellular carcinoma (HCC). However, advanced stages are not selected for transplant, based on the United Network for Organ Sharing selection criteria's. Nowadays, molecular biology-based techniques constitute an excellent option to better understand HCC origin differentiation and biological behavior. Moreover, microarray technology is a powerful tool to address a variety of tumor tissues at molecular level and is actively used for the discovery of biomarkers in cancer research. This article will discuss published data in the field of HCC origin differentiation and its potential impact on outcomes following liver transplantation. Although preliminary results are presented, these findings encourage the use of gene-expression profiling microarrays for studying HCC biology and behavior and ultimately optimizing treatment success.

Molecular signatures of noncancerous liver tissue can predict the risk for late recurrence of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is an aggressive malignancy mainly due to tumor metastases or recurrence even after undergoing potentially curative treatment. There are two types of HCC recurrence. The early and late tumor recurrences appear in distinct biological contexts, and their clinical courses are quite different. Therefore, it is important to precisely and distinctly discriminate the risk of each type of HCC recurrence. Many researchers have used DNA microarray technology to reclassify HCC with respect to its malignant potential. Some of these studies successfully identified specific gene-expression signatures derived from the cancerous tissues of HCC for predicting the early recurrence due to intrahepatic metastasis. However, there are no well-defined predictors for late recurrence. Recently, a few studies have focused on the nontumorous portion of liver tissues to predict late recurrence, possibly due to de novo hepatocarcinogenesis based on the idea of "field cancerization." This study reviewed the possible value of a gene-expression analysis of noncancerous liver tissue to clarify the risk for multicentric late recurrence of HCC. These findings may have important implications for chemopreventive strategies and tailored surveillance programs. Furthermore, this approach may also be applicable to other multifocal tumors, such as head and neck carcinoma.

Prognostic significance of the DNA-index in liver transplantation for hepatocellular carcinoma in cirrhosis

OBJECTIVE

This study was conducted to evaluate the prognostic significance of the tumor DNA index in patients receiving liver transplantation for hepatocellular carcinoma (HCC) in cirrhosis.

BACKGROUND

In patients suffering from HCC in cirrhosis, the current selection for liver transplantation does not optimally achieve the goal to simultaneously maximize the number of viable transplant candidates and reject the smallest number of those who could have benefited. This is the first report on the prognostic significance of the tumor DNA index.

PATIENTS AND METHODS

From 1988 to 2007, liver transplantation for HCC in cirrhosis was performed in 246 consecutive patients. The DNA-index was determined by Feulgen staining and semiautomatical image analysis. Interpretation of DNA histograms followed the recommendations outlined in the European Society for Analytical Cellular Pathology consensus report on diagnostic DNA image cytometry.

RESULTS

A DNA-index <or=1.5 was detected in the HCC of 159 patients (65%). Five- and 10-year post-transplant survival rates in this group were 86% and 80%, respectively. The DNA-index exceeded 1.5 in 87 patients (35%). These patients had 5- and 10-year survival rates of 27% and 6%, respectively, which were significantly lower than in the DNA-index <or=1.5 group (P < 0.0001). On univariate analysis, DNA-index, vascular invasion, fulfillment of the Milan criteria, and histopathological grading were prognostic parameters. In the multivariate analysis, only DNA-index (odds ratio: 11.9; 95% confidence interval: 7.1-20.0; P < 0.0001) and vascular infiltration (odds ratio: 1.7; 95% confidence interval: 1.1-2.6; P < 0.01) were identified as prognostic variables.

CONCLUSION

This is the first study to describe the DNA-index as a strong prognostic indicator after liver transplantation for HCC in cirrhosis. At this time, determination of the DNA-index is likely to be the most promising diagnostic tool in the selection of transplant candidates.

Proteomics and liver fibrosis: identifying markers of fibrogenesis

Chronic hepatic disease damages the liver and the resulting wound-healing process might lead to liver fibrosis and subsequent cirrhosis development. Fibrosis is the excessive deposition of extracellular matrix (ECM) in the tissue as consequence of chronic liver damage. The fibrotic response triggers almost all of the complications of end-stage liver disease, including portal hypertension, ascites, encephalopathy, synthetic dysfunction and impaired metabolic capacity. Thus, efforts to understand and attenuate fibrosis have direct clinical implications. Reliable, accurate, disease-specific, noninvasive biomarkers of fibrosis and fibrogenesis in order to prevent or minimize the impact of the chronic liver disease progression are a critical need. This review aims to provide an overview of the possibilities that proteome technology can offer to the knowledge, diagnosis and prognosis of liver fibrosis.

Natural history and therapeutic management of recurrent hepatocellular carcinoma after liver transplantation

While the natural history and appropriate diagnostic and management practices are relatively well defined for hepatocellular carcinoma (HCC), data are scarce concerning the characteristic features and treatment modalities for recurrent HCC after liver transplantation. The time of recurrence appears to impact survival more significantly than localization, but to date, guidelines for therapeutic management of recurrent HCC have not been established. Data in the literature shows that late and unifocal recurrence has a better prognosis when treated by surgery or radiofrequency. In the event of early recurrence, surgery cannot be recommended due to the lack of evidence and the high risk of advanced disease. Systemic therapy can be discussed in a situation of multifocal recurrence. Proliferative signal inhibitors exhibit both immunosuppressive and antiproliferative properties and liver transplantation teams tend to introduce such treatment despite the lack of extensive data.

Genes involved in viral carcinogenesis and tumor initiation in hepatitis C virus-induced hepatocellular carcinoma

The role of chronic hepatitis C virus (HCV) in the pathogenesis of HCV-associated hepatocellular carcinoma (HCC) remains controversial. To understand the transition from benign to malignant, we studied the gene expression patterns in liver tissues at different stages, including normal, cirrhosis, and different HCC stages. We studied 108 liver tissue samples obtained from 88 distinct patients (41 HCV-cirrhotic tissues, 17 HCV-cirrhotic tissues from patients with HCC, and 47 HCV-HCC tissues). Differentially expressed genes (DEG) were studied by use of high-density oligonucleotide arrays. Among probe sets identified as differentially expressed via the F test, all pairwise comparisons were performed. Cirrhotic tissues with and without concomitant HCC were further evaluated, and a classifier was used to predict whether the tissue type was associated with HCC. Differential expression profiles were analyzed using Interaction Networks and Functional Analysis. Characteristic gene signatures were identified when normal tissue was compared with cirrhosis, cirrhosis with early HCC, and normal with HCC. Pathway analysis classified the cellular and biological functions of the DEG as related to cellular growth and proliferation, cell death and inflammatory disease in cirrhosis; cell death, cell cycle, DNA replication, and immune response in early HCCs; and cell death, cell growth and proliferation, cell cycle, and DNA repair in advanced HCCs. Characteristic gene signatures were identified at different stages of HCV-HCC progression. A set of genes were identified to predict whether the cirrhotic tissue was associated with HCC.

Total tumor volume predicts risk of recurrence following liver transplantation in patients with hepatocellular carcinoma

Criteria for the selection of candidates for liver transplantation in the presence of hepatocellular carcinoma (HCC) should accurately predict posttransplant recurrence while not excluding excessive numbers of patients from candidacy. Existing criteria are challenged by the limited accuracy of radiological assessment. The total tumor volume (TTV) was calculated by the addition of the volume of each individual tumor. A preliminary analysis was carried out on HCC patient data from the Alberta Liver Transplant Program (52 patients) and then validated on the populations of the Universities of Toronto and Colorado programs (154 and 82 patients). A TTV cutoff of 115 cm(3) was chosen on the basis of the risk of recurrence with use of a receiver operating characteristic curve. Radiology correlated more closely to pathology with TTV than with Milan and University of California at San Francisco (UCSF) criteria (91% versus 69% and 75% of patients, P < 0.0001). Although more patients met qualifying criteria for transplant with TTV (28%-53% more than Milan and 16%-26% more than UCSF), no deterioration of outcome was demonstrated in an analysis of patients within TTV < or = 115 cm(3) in comparison with those meeting Milan or UCSF classifications at all institutions. Patients with TTV > 115 cm(3) experienced more recurrences and lower patient survival in the Alberta and Colorado series (P < 0.05). When TTV with a cutoff of 115 cm(3) is used for candidate selection, the accuracy of pretransplant radiological assessment is enhanced, with posttransplant outcomes not different from those achieved with Milan and UCSF classifications despite a more inclusive patient population.

A novel model measuring the harm of transplanting hepatocellular carcinoma exceeding Milan criteria

No empirical studies have defined the posttransplant survival that would justify expansion of the Milan criteria for liver transplantation of hepatocellular carcinoma. We created a Markov model comparing the survival benefit of transplantation for a patient with >Milan HCC, versus the harm caused to other patients on the waiting list. In the base-case analysis, the strategy of transplanting the patient with >Milan HCC resulted in a 44% increased risk of death and a utility loss of 3 quality-adjusted years of life across the pre- and posttransplant periods for a nationally representative cohort of patients on the waiting list. This harm outweighed the benefit of transplantation for a patient with >Milan HCC having a 5-year posttransplant survival of less than 61%. This survival threshold was most sensitive to geographic variations in organ shortage, with the threshold varying from 25% (Region 3) to >72% (Regions 1, 5, 7 and 9). In conclusion, expansion of the Milan criteria will require demonstrating high survival rates for the newly eligible patients-approximately 61% at 5 years after transplantation. In regions with less severe organ shortage, a more aggressive approach to transplanting these patients may be justified.

Translational microarray systems for outcome prediction of hepatocellular carcinoma

DNA microarray technology has revolutionized our understanding of the molecular basis of hepatocellular carcinoma (HCC), one of the most fatal human cancers with a high recurrence rate. Many researchers have used DNA microarray technology to reclassify HCC with respect to metastatic potential and to develop predictors for the outcome of HCC. However, developed predictors have reached the level only of small retrospective studies, and their current status is far from that required for clinical use. This is due to the lack of transparent data, the high cost and data instability associated with the high dimensionality of the technique, the infancy of bioinformatics, and the complicated nature of recurrent HCC. This comprehensive review summarizes: (i) class comparison studies to identify genes or pathways involved in HCC metastasis (ii) class discovery studies that have resulted in the identification of a new molecular subclass of HCC with respect to metastasis, and (iii) class prediction studies to develop multidimensional predictors for HCC outcome. We also discuss issues that need to be addressed so that the power of array-based predictors can be estimated prospectively in large independent cohorts of HCC patients.

Adenovirus-mediated restoration of expression of the tumor suppressor gene DLC1 inhibits the proliferation and tumorigenicity of aggressive, androgen-independent human prostate cancer cell lines: prospects for gene therapy

Our recent study showing highly recurrent loss of function of DLC1 (deleted in liver cancer 1), a tumor suppressor gene in primary prostate carcinoma (PCA), implicates this gene in the pathogenesis of this disease. To evaluate the response of PCA to oncosuppressive activity of DLC1, we examined now the effects of adenoviral vector for human DLC1 transduction into the DLC1-deficient, androgen-independent (AI) and aggressive human PCA cell lines PC-3 and C4-2-B2. Adenovirus-mediated restoration of DLC1 expression inhibited the proliferation, invasiveness and anchorage-independent growth of PC-3 and C4-2-B2 cells in vitro as well as the tumorigenicity of PC-3 cells in nude mice. It also induced cell-cycle arrest, inhibited the activation of RhoA and the formation of actin stress fibers. DLC1 induced apoptosis in C4-2-B2 cells, whereas it did not elicit such an effect in PC-3 cells. The abundance of the antiapoptotic protein Bcl-2 was greater in PC-3 cells than in C4-2-B2 cells, and PC-3 cells were rendered sensitive to DLC1-induced apoptosis by treatment with the Bcl-2 inhibitor HA14-1. These results suggest that adenovirus-mediated DLC1 transfer, alone or together with other agents, such as inhibitors of Bcl-2 or histone deacetylase, might prove effective in the treatment of aggressive, AI-PCA.

Future of molecular profiling of human hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a fatal disease occurring worldwide and developing mainly in chronic liver diseased patients. Despite routine screening of individuals at high risk, most of the patients are diagnosed at late stages of HCC. In addition, the recurrence rate after surgical resection of small tumors is high. Molecular profiling, including expression analysis, comparative genomics and proteomics, provides powerful tools to gain insight into the molecular mechanisms underlying carcinogenesis. Advances in bioinformatics have also allowed for the evaluation of large data sets. Therefore, molecular profiling of HCC using a Biological Expression Network Discovery (BLEND) strategy that integrates global molecular profiling data, including mRNA, miRNA, DNA methylation and DNA copy numbers from both the tumor and the surrounding microenvironment, along with mechanistic studies, may improve the diagnosis, treatment and prognosis of HCC patients. Such an approach will provide mechanistic insight into the pathogenesis of HCC, potentially leading to personalized medicine and the identification of new therapeutic targets.

DLC-1:a Rho GTPase-activating protein and tumour suppressor

The deleted in liver cancer 1 (DLC-1) gene encodes a GTPase activating protein that acts as a negative regulator of the Rho family of small GTPases. Rho proteins transduce signals that influence cell morphology and physiology, and their aberrant up-regulation is a key factor in the neoplastic process, including metastasis. Since its discovery, compelling evidence has accumulated that demonstrates a role for DLC-1 as a bona fide tumour suppressor gene in different types of human cancer. Loss of DLC-1 expression mediated by genetic and epigenetic mechanisms has been associated with the development of many human cancers, and restoration of DLC-1 expression inhibited the growth of tumour cells in vivo and in vitro. Two closely related genes, DLC-2 and DLC-3, may also be tumour suppressors. This review presents the current status of progress in understanding the biological functions of DLC-1 and its relatives and their roles in neoplasia.