Tumor Long Interspersed Nucleotide Element-1 (LINE-1) Hypomethylation in Relation to Age of Colorectal Cancer Diagnosis and Prognosis

Simple Summary The rising incidence of early-onset cancers diagnosed before 50 years in many body sites (including the colorectum) is a growing concern. Despite the many studies of early-onset colorectal cancer, the characteristics of colorectal cancer diagnosed at age 50 or slightly after (close to age 50) have not been adequately examined. Although epigenetic alterations are considered to play a role in early-onset colorectal cancer, the association of LINE-1 hypomethylation (that reflects global DNA hypomethylation) with the age of colorectal cancer diagnosis has not been thoroughly clarified. Using a database of 1356 colorectal cancers, we found that tumor LINE-1 hypomethylation was increasingly more common with decreasing age of colorectal cancer diagnosis and was associated with higher colorectal cancer-specific mortality. Our findings support the "age continuum" model that has substantial implications in research on cancers in not only the colorectum but also many other body sites. Evidence indicates the pathogenic role of epigenetic alterations in early-onset colorectal cancers diagnosed before age 50. However, features of colorectal cancers diagnosed at age 50-54 (hereafter referred to as "intermediate-onset") remain less known. We hypothesized that tumor long interspersed nucleotide element-1 (LINE-1) hypomethylation might be increasingly more common with decreasing age of colorectal cancer diagnosis. In 1356 colorectal cancers, including 28 early-onset and 66 intermediate-onset cases, the tumor LINE-1 methylation level measured by bisulfite-PCR-pyrosequencing (scaled 0 to 100) showed a mean of 63.6 (standard deviation (SD) 10.1). The mean tumor LINE-1 methylation level decreased with decreasing age (mean 64.7 (SD 10.4) in age >= 70, 62.8 (SD 9.4) in age 55-69, 61.0 (SD 10.2) in age 50-54, and 58.9 (SD 12.0) in age p < 0.0001). In linear regression analysis, the multivariable-adjusted beta coefficient (95% confidence interval (CI)) (vs. age >= 70) was -1.38 (-2.47 to -0.30) for age 55-69, -2.82 (-5.29 to -0.34) for age 50-54, and -4.54 (-8.24 to -0.85) for age <50 (P-trend = 0.0003). Multivariable-adjusted hazard ratios (95% CI) for LINE-1 methylation levels of <= 45, 45-55, and 55-65 (vs. >65) were 2.33 (1.49-3.64), 1.39 (1.05-1.85), and 1.29 (1.02-1.63), respectively (P-trend = 0.0005). In conclusion, tumor LINE-1 hypomethylation is increasingly more common with decreasing age of colorectal cancer diagnosis, suggesting a role of global DNA hypomethylation in colorectal cancer arising in younger adults.