Many normal tissues undergo age-related drift in DNA methylation, providing a quantitative measure of tissue age. Here, we identify and validate 781 CpG islands (CGI) that undergo significant methylomic drift in 232 normal colorectal tissues and show that these CGI continue to drift in neoplasia while retaining significant correlations across samples. However, compared with normal colon, this drift advanced ($3-4-fold) faster in neoplasia, consistent with increased cell proliferation during neoplastic progression. The observed drift patterns were broadly consistent with modeled adenoma-to-carcinoma sojourn time distributions from colorectal cancer incidence data. These results support the hypothesis that, beginning with the founder premalignant cell, cancer precursors frequently sojourn for decades before turning into cancer, implying that the founder cell typically arises early in life. At least 77% to 89% of the observed drift variance in distal and rectal tumors was explained by stochastic variability associated with neoplas-tic progression, whereas only 55% of the variance was explained for proximal tumors. However, gene-CGI pairs in the proximal colon that underwent drift were significantly and primarily negatively correlated with cancer gene expression, suggesting that methylomic drift participates in the clonal evolution of colorectal cancer. Methylomic drift advanced in colorectal neoplasia, consistent with extended sojourn time distributions, which accounts for a significant fraction of epigenetic heterogeneity in colorectal cancer. Importantly, these estimated long-duration premalignant sojourn times suggest that early dietary and lifestyle interventions may be more effective than later changes in reducing colorectal cancer incidence. Significance: These findings present age-related methylomic drift in colorectal neoplasia as evidence that premalignant cells can persist for decades before becoming cancerous. See related commentary by Sapienza, p. 437

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The identification of genetic mutations linked to breast cancer has made it possible to test for the genetic predisposition to this disease. However, though this test may provide certain benefits, there are also potential risks involved with the testing process, including social and economic considerations. In light of these potential risks, we sought to determine what information individuals are receiving in the informed decision making process. To learn the minimal amount of information the actual testees receive, we obtained 10 informed consent forms from seven different testing facilities. These testing centers include the major sources of BRCA1 and BRCA2 mutation testing in the United States at this time. We analyzed the content of these forms by developing content categories and scoring them appropriately. We found all ten forms discussed in varying ways and to varying degrees the purpose of genetic testing, limitations of the test, implications of both positive and negative results, and confidentiality procedures; most, but not all, addressed various psychological and insurance risks. Overall, the forms demonstrated substantial variation in content and organization, underlining the need for more discussion and research on the purpose, nature, and effectiveness of informed consent forms for this type of genetic test.

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