Introduction: Colorectal carcinomas are the 2nd leading cause of cancer-related deaths in the US and in Puerto Rico. Recent literature reports a dramatic increase in the incidence of sporadic colorectal cancer (CRC) in patients <50 years old among Hispanics (45%) compared to other ethnic groups in the same age range. This increase has been observed despite a decrease in the incidence of CRC in older individuals, probably due to the routine screening among those ≥50 years old. This highlights the imperative need for non-invasive diagnostic tool for individuals <50 years in order to reduce this age-ethnic cancer health disparity and increase the number of cases diagnosed at earlier, more treatable stages. Epigenetic changes in cell-free plasma DNA have been studied as non-invasive CRC diagnostic markers, but a gene panel with the diagnostic accuracy necessary for clinical use has not been defined. The CpG island methylator phenotype (CIMP), characterized by promoter hypermethylation, is one of the epigenetic mechanisms that contribute to colorectal carcinogenesis.
Aim: The aim of this study was to compare the methylation profile of 5 genes between early-onset (EO CRC; <50 years) and late-onset (LO CRC; >50 years) CRC patients and to determine if EO CRC-specific methylation markers identified in the tumor were detectable in plasma.
Methods: Methylation-specific PCR (MSP) was used to evaluate methylation status of 5 CIMP-specific gene promoters (CACNAG1, NEUROG1, RUNX3, SOCS1 and MLH1) \in 25 CRC tissues (6 EO CRC; 19 LO CRC). The CACNAG1 methylation status was evaluated in 20 plasma samples from LO CRC patients via MSP. Statistical significance was determined using Fisher Exact test (STATA 10.0).
Results: The methylation status of 5 genes was evaluated in 25 tumors from Hispanic CRC patients. Methylation analysis shows that CACNAG1 was predominantly methylated in EO CRC tumors (50%) whereas it was methylated in 3 out of 19 (26.6%) in LO CRC. NEUROG1, RUNX3 and MLH1 were only methylated in LO CRC tissues. To evaluate if detection of the methylation status of CACNAG1 was feasible in plasma, we used the same approach and found that this gene was unmethylated in the LO CRC plasma samples assayed (18 of 18 (100%); 2 samples were not detected using this method).
Discussion: Preliminary analyses using this 5 gene methylation biomarker panel support that Hispanic EO CRC tumors have a distinct methylation profile. The CACNAG1 gene was more methylated in EO CRC than in LO CRC tumors. Similar to what was detected in LO CRC tissue, CACNAG1 was unmethylated in all of the plasma samples detected supporting its potential as plasma biomarker. Further analyses with a greater number of CRC tissues and plasma samples are needed to confirm if CACNAG1 is an early-onset CRC-specific biomarker. The fact that the CACNAG1 methylation status can be determined in plasma makes this biomarker appealing for future investigation into its potential as a non-invasive EO CRC screening biomarker.
Citation Format: Maria Gonzalez-Pons, Heriberto M. Rodríguez-Arroyo, Cristina Nuñez, Mercedes Y. Lacourt, Sharon Fonseca-Williams, Raul Bernabe-Dones, Marcia Cruz-Correa. Detection of early-onset CRC tumor methylation biomarkers in plasma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5363. doi:10.1158/1538-7445.AM2013-5363