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Epigenetic Signatures of Familial Cancer Are Characteristic of Tumor Type and Family Category

¹ Department of Medical Genetics, University of Helsinki; ² Health and Work Ability, Biological Mechanisms and Prevention of Work-Related Diseases, Finnish Institute of Occupational Health; ³ Department of Pathology, Haartman Institute and HUSLAB, University of Helsinki and Helsinki University Central Hospital, Helsinki, Finland; and ⁴ Helsinki Institute for Information Technology, Laboratory of Computer and Information Science, Helsinki University of Technology, Espoo, Finland

Requests for reprints: Emmi I. Joensuu, Department of Medical Genetics, Biomedicum Helsinki, University of Helsinki, P. O. Box 63, FIN-00014 Helsinki, Finland. Phone: 358-919125189; Fax: 358-919125105; E-mail: emmi.joensuu{at}helsinki.fi.

Key Words: promoter methylation • tumor suppressor gene • colorectal cancer • endometrial cancer • familial cancer

Tumor suppressor genes (TSG) may be inactivated by methylation of critical CpG sites in their promoter regions, providing targets for early detection and prevention. Although sporadic cancers, especially colorectal carcinoma (CRC), have been characterized for epigenetic changes extensively, such information in familial/hereditary cancer is limited. We studied 108 CRCs and 63 endometrial carcinomas (EC) occurring as part of hereditary nonpolyposis CRC, as separate familial site-specific entities or sporadically, for promoter methylation of 24 TSGs. Eleven genes in CRC and 6 in EC were methylated in at least 15% of tumors and together accounted for 89% and 82% of promoter methylation events in CRC and EC, respectively. Some genes (e.g., CDH13, APC, GSTP1, and TIMP3) showed frequent methylation in both cancers, whereas promoter methylation of ESR1, CHFR, and RARB was typical of CRC and that of RASSF1(A) characterized EC. Among CRCs, sets of genes with methylation characteristic of familial versus sporadic tumors appeared. A TSG methylator phenotype (methylation of at least 5 of 24 genes) occurred in 37% of CRC and 18% of EC (P = 0.013), and the presence versus absence of MLH1 methylation divided the tumors into high versus low methylation groups. In conclusion, inactivation of TSGs by promoter methylation followed patterns characteristic of tumor type (CRC versus EC) and family category and was strongly influenced by MLH1 promoter methylation status in all categories. Paired normal tissues or blood displayed negligible methylation arguing against a constitutional methylation abnormality in familial cases. [Cancer Res 2008;68(12):4597–605]