The risk of cancer varies significantly across different body tissues, with a higher risk for colon and breast tissues than brain or bone tissues. Prior to tumor formation, normal tissues show abnormal patterns of DNA methylation—a type of epigenetic change that can affect gene activity without altering the DNA sequence.

Given that aberrant DNA methylation precedes tumor development and varies across cell types, researchers examined whether this epigenetic mark could explain variations in cancer risk across tissues. The authors used previously established genetic databases to collect extensive DNA methylation profiles from normal human tissues.

The levels of DNA methylation in different tissues were significantly correlated with lifetime risk for different cancer types. For example, colon and breast tissues showed much higher DNA methylation levels than brain tissues. For many different cell types, DNA methylation was mostly concentrated in a small number of molecules, suggesting that this epigenetic change could mark cancer-prone cells in a population.

Taken together, the findings suggest that the risk of cancer in a given tissue may be correlated with the number of abnormally methylated precancerous cells in that tissue. According to the authors, the results support the idea that genetic and epigenetic changes play critical roles in tumor biology.