Left-sided early-onset vs late-onset colorectal carcinoma: histologic, clinical, and molecular differences.

OBJECTIVES Carcinomas of the left colon represent a neoplasm of older patients (late onset), but epidemiologic evidence has been showing an increasing incidence in patients 50 years or younger (early onset). In this study, we investigate pathologic and molecular features of early- and late-onset carcinoma of the left colon. METHODS We selected 22 patients 50 years or younger and 21 patients 70 years or older with left-sided colorectal carcinoma (CRC). All samples were evaluated for pathologic features, microsatellite instability, and KRAS and BRAF mutations. Moreover, both groups were analyzed to identify CpG island methylator phenotype features and assessed with restriction landmark genome scanning (RLGS) to unveil differential DNA methylation patterns. RESULTS Early-onset patients had advanced pathologic stages compared with late-onset patients (P = .0482). All cases showed a microsatellite stable profile and BRAF wild-type sequence. Early-onset patients (43%) more frequently had mutations at KRAS codon 12 compared with late-onset patients (14%) (P =.0413). RLGS showed that patients younger than 50 years who had CRC had a significantly lower percentage of methylated loci than did patients 70 years or older (P = .04124), and differential methylation of several genomic loci was observed in the two groups. CONCLUSIONS Our results suggest that left-sided CRCs may present differential patterns of aberrant DNA methylation when they are separated by age.