Background: Since there is a predilection of some clinical and molecular features for a given tumor location, we assessed whether this can be confirmed in late-onset colorectal cancer (LOCRC). Methods: We analyzed clinical and molecular characteristics of LOCRC at different tumor locations in order to determine if there are differential phenotypes related with the location in the colon. Results: Right colon cancers showed features associated with sporadic Microsatellite Instability: predominance of female cases and BRAF mutations, and an important mucinous component. Left colon cancers developed a higher number of polyps and multiple primary CRCs, showed the strongest familial component, and had better prognosis. Rectal cancers showed a predominantly sporadic phenotype, with worse prognosis and a CpG Island Methylator Phenotype (CIMP)-High. No copy number alterations (CNAs) greater than or equal to 50% were observed in this LOCRC group, and the most recurrent alterations were losses at 5q13 and 14q11, and gains at 7q11, 7q21-q22, 19p13-p12, 19q13 and 20p11-q11. KRAS and PIK3CA were the only mutated genes showing differences according to the tumor location, mainly for right colon cancers. Conclusions: Categorizing LOCRC according to tumor location appears to be an adequate first step to resolving the heterogeneity of this subset of CRC.
Overall design
A total of 100 consecutive individuals with colorectal cancer diagnosed at an age of 70 years or older were collected from our institution, starting from January 2002. All patients, or a first degree relative in case of death of the index case, provided written consent. 86 of these samples could be adequately processed for Array Comparative Genomic Hybridisation (a-CGH).
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