HCC is a common type of cancer, with approximately 260 000 new cases each year. However, specific changes of gene expression in HCC remain obscure. The expression of genes for hepatocytic growth factor c-myc protooncogene was analyzed by Yongqiang et al., 2003; Kim et al., 2005. It has been suggested that the rate of tumor growth is determined by the balance between cell proliferation and cell death: only when the rate of proliferation exceeds that of death does tumor growth occur. Alteration in oncogene expression may, therefore, potentially act on cancer cells by lowering their rate of apoptosis, raising their rate of proliferation, or both (Yongqiang et al., 2003). Data published to date indicate that oncogene amplification is one of the most common genetic alterations found in human cancers. Examination of regional c-myc gene amplification within breast tumors showed that alteration of this gene can occur at an early in-situ stage of tumor progression and often does not persist in late-stage nodal metastasis. The product of the c-myc oncogene is an important nuclear DNA-binding protein that seems to play critical roles in the regulation of cell growth and division. The c-myc oncoprotein is activated to cause cell transformation by overexpression, resulting in intracellular accumulation (Kim et al., 2005).
Data presented in this study showed that all control non-neoplastic cases showed positive low (+) c-myc expression. Dysplastic hepatic nodules showed high (+++) expression of c-myc in 50% of high-grade dysplasia and moderate (++) c-myc expression in 25% of cases examined compared with low-grade dysplastic cases in which 16.7% of cases showed moderate c-myc expression and 83.3% of them showed low (+) c-myc expression and none of them showed high c-myc expression. As regard HCC cases, 50% of them showed high c-myc expression and 25% showed moderate c-myc expression. The relationship was statistically significant (P<0.05). These results may support the assumption that alterations in the c-myc protein level are involved in formation and progression of low-grade DNs into high-grade DNs and early HCC. Thus, there is c-myc overexpression at the time of tumor presentation. Sustained c-myc overexpression results in persistent proliferation of hepatocytes, and increased occurrence of HCC development may be through activation of transforming growth factor due to an unrestrained cell cycle progression of neoplastic hepatocytes by the disruption of the cyclin D-pRb-E2F pathway (Young et al., 2000; Yoshiji et al., 2002).
With regard to the relation to the tumor grade, examined cases of HCC showed high c-myc expression in 14 (87.5%) of 16 GIII cases examined compared with none of 11 (9.1%) GI cases. These results were in accordance with the data discussed by Cui et al. (2004) and Kim et al. (2005) in which they found that c-myc overexpression was related to tumor progression and differentiation. Moreover, they stated that this overexpression has no direct relation to the recurrence, which was a later biological behavior developed at an advanced stage of the tumor. The tumor differentiation in the c-myc positive group was lower than that in the c-myc negative group. A study on the biological behavior of c-myc protein indicates that besides being a transcriptional factor it is important for cell growth and differentiation (Yu et al., 2003).
As regards the relation to TNM stage, five (100%) of SIV cases showed high c-myc expression in relation to two of seven cases (28.6%) of SI cases. In consistent to these results, Berns et al. (1996) found that the occurrence of c-myc oncogene amplification in breast cancer has been related to a poor prognosis.
HCC is known to receive its blood supply principally from the hepatic arteries. Recent studies have reported differences in the vascular supply, especially arterial supply among low-grade and high-grade DNs and HCCs. Increased expression of vascular endothelial growth factor (VEGF) has been reported in HCC. In addition, VEGF may play an important role in the early phases of hepatocarcinogenesis, but little issues are discussed in the role of CD34 in early and late stages of hepatic carcinogenesis (Young et al., 2000).
Angiogenesis is very common within normal and pathologic tissues and is regulated by many factors, such as VEGF, hypoxia-inducible factor 1 α, human macrophage metalloelastase, basic fibroblast growth factor, and so on (Ravi et al., 2000; Yoshiji et al., 2002). Vessels interact with tumor cells to construct microenvironment of tumor (Gorrin-Rivas et al., 2000). CD34, which is expressed in blood stem cells and neovessel endothelial cells, is the most distinctive marker for demonstrating vessel endothelial cells (Frachon et al., 2001), especially for demonstrating sinusoid-like vessels in tumor tissues (Gottschalk-Sabag et al., 1998). In this research, non-neoplastic control cases showed focal positive CD34 expression in sinusoids restricted to the periportal area, whereas the centrolobular sinusoids were negative. All dysplastic and HCC cases were positive for CD34 antibody in sinusoidal endothelial cells. High CD34 expression was seen in 75% of high-grade dysplastic hepatic cases examined and in 88% of HCC cases compared with low-grade dysplastic cases, which showed low CD34 expression in 66.7% of cases. This relationship was statistically significant (P<0.05). This means that the degree of sinusoidal capillarization and angiogenesis increased gradually according to the stepwise development of hepatocarcinogenesis, as it was higher in high-grade DNs and HCCs than in low-grade DNs. Therefore, the microvessels play an important role not only in occurrence and development of HCC, but also may be helpful to identify malignant lesions or precancerous lesions (high-grade DNs) from benign or low-grade DNs.
With regard to the relation to the tumor grade, examined cases of HCC showed high (+3) CD34 expression in 12 (75%) of 16 GIII cases examined compared with five (45.4%) of 11 GI cases that showed low (+1) CD34 expression, which was statistically significant (P<0.05). These results may indicate that angiogenesis and sinusoidal capillarization increased gradually as hepatocarcinogenesis progressed. These results are in accordance with the data discussed by Ohmori et al. (2001), who found that high expression of CD34 positive sinusoidal endothelial cells is a risk factor for HCC in a patient with chronic liver disease. In addition, Lu et al. (2004) found that MVD was higher in high-grade HCC than low-grade HCC. Taku et al. (2001) reported that fine sinusoidal capillaries were positive for CD34 in well-differentiated HCC whereas thick and peripheral vessels were positive for CD34 in moderately differentiated and poorly differentiated HCC and suggested that CD34 may be useful marker in the diagnosis of the hepatic DNs and assessing the degree of the differentiation of HCC. Other reports also showed that poor differentiation and portal invasion are significantly related to MVD (Nakashima et al., 1999). Yamamoto et al. (2001) demonstrated that sinusoidal capillarization occurring in well-differentiated HCC is related to dedifferentiation of parenchymal tumor cells. As regards the relation to TNM stage, four (80%) of five SIV cases showed high (+3) CD34 expression compared with four (57.1%) of seven SI cases that showed low (+1) CD34 expression (P<0.05). Similar to these results, Lu et al. (2004) found that increased MVD was associated with advanced stages of HCC, indicating that the density of neovascularization is correlated with metastasis, resulting in poor prognosis.
In this study, c-myc oncoprotein expression increased gradually as hepatocarcinogenesis progressed. Thus, c-myc oncoprotein expression is considered to contribute to the growth advantage in hepatocarcinogenesis. In addition, the degree of MVD determined by the degree of CD34 expression increased gradually according to the stepwise development of hepatocarcinogenesis. Moreover, the significant coexpression of CD34 and c-myc in HCC in this study strongly suggests an important role for these genes in malignant growth and progression.
In conclusion, c-myc and CD34 upregulations are greatly integrated in multistep hepatocellular carcinogenesis and also in prognosis and progression of HCC.
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