Research at the Pathology Division is based on a combination of clinicopathological observations and molecular and cellular biological analyses.

Alterations of DNA methylation are frequently observed in cancers associated with chronic inflammation and/or persistent infection with viruses or other pathogenic microorganisms, such as hepatitis B or C viruses and Epstein-Barr virus, or with cigarette smoking ⁽¹⁾. Alterations of DNA methylation have been noted even in the early and precancerous stages. On the other hand, in patients with cancers, aberrant DNA methylation was significantly associated with poorer tumor differentiation, tumor aggressiveness, and poor prognosis. Precancerous conditions showing alterations of DNA methylation may progress rapidly and evolve into more malignant cancers. Alteration of DNA methylation may thus become an indicator for carcinogenetic risk estimation and early diagnosis of cancers and a biological predictor of poor prognosis in patients with cancers ⁽¹⁾.

DNA methyltransferase 1 (DNMT1) overexpression was not a secondary result of increased cell proliferative activity, but was significantly correlated with the CpG island methylator phenotype, which is defined as frequent DNA hypermethylation of C-type CpG islands that are usually methylated in a cancer-specific (not age-dependent) manner ⁽¹⁾. For example, the immunohistochemically assessed DNMT1 protein expression score, reflecting the intensity and incidence of DNMT1 nuclear immunoreactivity, was increased even in low-grade cervical intraepithelial neoplasia in comparison with that in histologically normal squamous epithelium of the uterine cervix, and even further increased in higher-grade cervical intraepithelial neoplasia as compared with that in low-grade cervical intraepithelial neoplasia ⁽²⁾. The DNMT1 protein expression score remained at a plateau in microinvasive carcinoma (Stage IA) as compared with that in higher-grade cervical intraepithelial neoplasia. The score decreased with cancer invasion -it was lower in Stage IB or more advanced cancer as compared with that in Stage IA cancer, whereas proliferating cell nuclear antigen labeling index did not decrease with cancer invasion ⁽²⁾. Thus the DNMT1 protein expression score and proliferating cell nuclear antigen labeling index were not mutually correlated in squamous cell carcinoma of the uterine cervix. Progressively increasing expression of the DNMT1 protein begins at an early step of multistage cervical carcinogenesis.

Homozygous loss of the connective tissue growth factor gene (6q23.2) was detected in ovarian cancer cell lines using array-based comparative genomic hybridization ⁽³⁾. In primary ovarian cancer tissues, DNA methylation around the promoter region of the connective tissue growth factor gene was frequently observed and inversely correlated with its mRNA expression ⁽³⁾. Silencing of the connective tissue growth factor gene due to DNA hypermethylation may participate in ovarian carcinogenesis in a stage-dependent and/or histologic subtype- dependent manner. Other epigenetic and genetic alterations were screened in cancers arising from various organs ⁽⁴⁾.

Tumor-infiltrating lymphocytes represent one of the host immune responses to cancer ⁽⁵⁾. The prevalence of FOXP3+ regulatory T cells was significantly higher in the stroma of hepatocellular carcinomas than in the nontumorous liver parenchyma ⁽⁶⁾. The patient group with a higher prevalence of regulatory T cells infiltrating the hepatocellular carcinoma showed a significantly lower survival rate ⁽⁶⁾. The prevalence of regulatory T cells increased in a stepwise manner from precursor lesions and early hepatocellular carcinoma to advanced hepatocellular carcinoma, and that of CD8+ T cells decreased during the progression of hepatocarcinogenesis. Regardless of the presence of hepatitis virus infection or histopathologic evidence of hepatitis, the prevalence of regulatory T cells was significantly increased in nontumorous liver bearing primary hepatic tumors ⁽⁶⁾. Primary hepatic cancers develop in livers that are immunosuppressed by marked infiltration with regulatory T cells. A high prevalence of regulatory T cells infiltrating the hepatocellular carcinoma is thought to be an unfavorable prognostic indicator.

The prognostic value of the tumor architecture, tumor-associated vascular characteristics and expression of angiogenic molecules was examined in pancreatic endocrine tumors. Focal and intensive solid growth of tumor cells, a high endothelial cell proliferation index and high expression of the CXC chemokine CXCL-12 in tumor cells were significant indicators of an unfavorable prognosis ⁽⁷⁾. The expression of vascular endothelial growth factor-A did not identify aggressive tumors. High expression of CXCL-12 in tumor cells was significantly associated with hematogenous tumor spread, low microvessel density, high endothelial cell proliferation index, and the presence of large solid nests ⁽⁷⁾. CXCL-12 is a candidate molecule associated with neoangiogenesis in pancreatic endocrine tumors.

Dysadherin, a newly identified cancer- associated cell membrane glycoprotein, downregulates E-cadherin and promotes cancer metastasis. In synovial sarcoma, a mesenchymal tumor that exhibits an epithelial profile, overexpression of dysadherin was significantly correlated with reduced expressionin of E-cadherin ⁽⁸⁾. Synovial sarcoma patients with overexpresion of dysadherin survived for a significantly shorter time than those without dysadherin expression ⁽⁸⁾.

To clarify the significance of the extent of the esophageal and gastric cardiac mucosae at the esophagogastric junction, esophagectomy specimens from consecutive patients with middle and upper thoracic esophageal cancer were histopathologically examined. The mean length of the esophageal cardiac mucosa and gastric cardiac mucosa in short-segment Barrett's esophagus was significantly greater than that in non-short-segment Barrett's esophagus cases ⁽⁹⁾. The incidence of columnar epithelial islands in short-segment Barrett's esophagus was significantly higher than that in non- short-segment Barrett's esophagus cases ⁽⁹⁾. Esophageal cardiac glands and columnar epithelial islands might play a role in the development of short-segment Barrett's esophagus.

Other clinicopathological studies were also conducted to further the understanding of the pathogenesis of cancers and promote the diagnosis and treatment of various tumors ^(10-21)