To better understand both the inherited (genetic) and acquired (epigenetic) basis for SSP and tumor development, the investigators used whole-exome sequencing, genome-wide mutation detection, and DNA methylation profiling on multiple samples of both SSPs and FAPs.
They performed exome sequencing on DNA extracted from SSP samples from six patients diagnosed with typical SSP-type colon polyps via colonoscopy and pathology. The samples included one each from five patients and three taken from different portions of the colon in one patient. In all of the samples, BRAF-V600E was the only common somatic mutation detected. In the patient from whom the three SSP samples were taken, the mutation was found in each polyp, but not in grossly uninvolved colon from the same patient.
The investigators next performed genome-wide DNA methylation profiling on 15 colon biopsy samples from 11 patients, including five SSPs, two traditional serrated adenomas, three FAPs, two carcinomas, one grossly uninvolved tissue sample, and two normal tissue samples. They found that the BRAF-V600E mutation correlated with a unique and reproducible DNA methylation signature.
They then determined that the DNA methylation signature that they identified is associated with specific markers for molecular characterization of SSPs, and that these markers showed an approximately 3- to 30-fold increase in methylation levels in only SSP samples.