A high degree of LINE-1 hypomethylation is a unique feature of early-onset colorectal cancer

Objective Early-onset colorectal cancer (CRC) represents a clinically distinct form of CRC that is often associated with a poor prognosis. Methylation levels of genomic repeats such as LINE-1 elements have been recognized as independent factors for increased cancer-related mortality. The methylation status of LINE-1 elements in early-onset CRC has not been analyzed previously. Design We analyzed 343 CRC tissues and 32 normal colonic mucosa samples, including 2 independent cohorts of CRC diagnosed ≤50 years old (n = 188), a group of sporadic CRC >50 years (MSS n = 89; MSI n = 46), and a group of Lynch syndrome CRCs (n = 20). Tumor mismatch repair protein expression, microsatellite instability status, LINE-1 and MLH1 methylation, somatic BRAF V600E mutation, and germline MUTYH mutations were evaluated. Results Mean LINE-1 methylation levels (±SD) in the five study groups were early-onset CRC, 56.6% (8.6); sporadic MSI, 67.1% (5.5); sporadic MSS, 65.1% (6.3); Lynch syndrome, 66.3% (4.5) and normal mucosa, 76.5% (1.5). Early-onset CRC had significantly lower LINE-1 methylation than any other group (p<0.0001). Compared to patients with <65% LINE-1 methylation in tumors, those with ≥65% LINE-1 methylation had significantly better overall survival (p = 0.026, log rank test). Conclusions LINE-1 hypomethylation constitutes a potentially important feature of early-onset CRC, and suggests a distinct molecular subtype. Further studies are needed to assess the potential of LINE-1 methylation status as a prognostic biomarker for young people with CRC

A High Degree of LINE-1 Hypomethylation Is a Unique Feature of Early-Onset Colorectal Cancer

<div><h3>Objective</h3><p>Early-onset colorectal cancer (CRC) represents a clinically distinct form of CRC that is often associated with a poor prognosis. Methylation levels of genomic repeats such as LINE-1 elements have been recognized as independent factors for increased cancer-related mortality. The methylation status of LINE-1 elements in early-onset CRC has not been analyzed previously.</p> <h3>Design</h3><p>We analyzed 343 CRC tissues and 32 normal colonic mucosa samples, including 2 independent cohorts of CRC diagnosed ≤50 years old (n = 188), a group of sporadic CRC >50 years (MSS n = 89; MSI n = 46), and a group of Lynch syndrome CRCs (n = 20). Tumor mismatch repair protein expression, microsatellite instability status, LINE-1 and <em>MLH1</em> methylation, somatic <em>BRAF</em> V600E mutation, and germline <em>MUTYH</em> mutations were evaluated.</p> <h3>Results</h3><p>Mean LINE-1 methylation levels (±SD) in the five study groups were early-onset CRC, 56.6% (8.6); sporadic MSI, 67.1% (5.5); sporadic MSS, 65.1% (6.3); Lynch syndrome, 66.3% (4.5) and normal mucosa, 76.5% (1.5). Early-onset CRC had significantly lower LINE-1 methylation than any other group (p<0.0001). Compared to patients with <65% LINE-1 methylation in tumors, those with ≥65% LINE-1 methylation had significantly better overall survival (p = 0.026, log rank test).</p> <h3>Conclusions</h3><p>LINE-1 hypomethylation constitutes a potentially important feature of early-onset CRC, and suggests a distinct molecular subtype. Further studies are needed to assess the potential of LINE-1 methylation status as a prognostic biomarker for young people with CRC.</p> </div

Clinical, pathological and molecular features of patients according to the LINE-1 methylation levels.

*<p>P value was calculated by t-test.</p>1<p>Including first and second degree relatives.</p>2<p>MSI-H and/or loss of expression of MMR proteins by immunohistochemistry.</p

LINE-1 methylation results in different clinical subgroups.

<p>CRC, colorectal cancer; SD, standard deviation.</p><p>Mann Whitney test was used to compare the LINE-1 values.</p>1<p>Values for comparison between normal colonic mucosa and other groups of CRC.</p>2<p>Values for comparison between early onset CRC (n = 185) and other groups of CRC.</p

Clinical, pathological and molecular features of patients with mismatch repair deficiency.

1<p>MSI-H and/or loss of expression of MMR proteins by immunohistochemistry.</p>2<p>MSS and normal expression of MMR proteins by immunohistochemistry.</p>3<p>Including first and second degree relatives; Lynch syndrome-associated neoplasia includes: endometrium, stomach, ovaries, urinary tract, small intestine, pancreas, bile ducts, brain or sebaceous glands.</p>4<p>Signet ring cells and/or Crohn’s-like lymphocytic reaction and/or tumor infiltrating lymphocytes and/or medullary growth pattern and/or anaplastic tumor.</p

Kaplan–Meier survival curves depicting the effect of LINE-1 methylation on 3-year overall survival in early-onset CRC patients.

<p><i>Vertical tick marks</i> indicate censored events. The green line represents survival in CRCs with LINE-1 hypomethylation <65% (n = 92) and the blue line represents LINE-1 methylation ≥65% (n = 23). p value for log rank and Fisher’s exact test are shown.</p