Introduction: Colorectal cancer accounts for a significant fraction of cancer-related mortalities, but has proven to be surprisingly refractory to consensus pathological and molecular subclassification. Similarly, little is known about the molecular profiles of colorectal cancer cells-of-origin. DNA methylation is an important epigenomic marker of cellular identity and can therefore be used to infer cancer cells-of-origin.
Methods: Infinium 450k data from colorectal cancer samples provided by “The Cancer Genome Atlas” was applied to a consensus clustering algorithm. The identified epigenetic subgroups were tested for features including well established clinical parameters or subgroup specific gene expression. Additionally, the subgroups were compared with Infinium 450k data of non-malignant colorectal adenomas. Finally, clinical significance was addressed by testing for subgroup specific overall survival rates.
Results: Analysis of the TCGA dataset defined 5 distinct epigenetic subtypes of human colorectal cancer. These subgroups showed an overlap to the microsatellite instability phenotype and the CpG island methylator phenotype. Gene expression based analysis revealed that the subtypes also form a continuum of epigenetic programs reflecting various intestinal crypt cell differentiation stages. Patient survival correlated with the differentiation stage, with a particular poor prognosis for patients with stem cell-related signatures. Interestingly, its prognostic potential outperformed a recently established gene expression-based classifier. Finally, non-malignant colorectal adenomas could be classified into the same methylation subtypes, reflecting their shared cell-types of origin with carcinomas
Conclusion: Our results establish a novel and clinically relevant approach for colorectal cancer classification and illustrate how differences in the cell-type of origin shape the tumor methylome.
Citation Format: Felix Bormann, Manuel Rodríguez-Paredes, Yehudit Bergman, Heinz G. Linhart, Frank Lyko. Cell-of-origin differentiation stages define methylation-based subtypes of human colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4350. doi:10.1158/1538-7445.AM2017-4350