Serrated colon polyps are present in = 20% of patients undergoing routine screening colonoscopy. Serrated polyps are divided into sessile serrated and hyperplastic polyps and are often difficult to differentiate by endoscopic and histological examination. Although serrated polyps were previously considered harmless, recent studies provide evidence that sessile serrated polyps account for 20-30% of all colon cancers. We propose a multilateral approach to identify molecular diagnostic markers for sessile serrated polyps that are predictive of increased colon cancer risk. We will use the most innovative next generation sequencing technology to define the complete small RNA (< 200 nt) transcriptome in both serum and biopsy specimens from 20 patients with an exaggerated phenotype of sessile serrated polyps, known as serrated polyposis syndrome (SPS). The syndrome is defined as patients with = 5 sessile serrated polyps proximal to the sigmoid colon, two of which are > 1cm diameter, or patients with > 20 serrated polyps at any site in the large bowel. The age of presentation (often < 40 yrs) and multiplicity of lesions suggests a genetic predisposition, but it basis remains unknown and familial occurrence is unusual. To achieve this goal we have developed one of the largest cohorts of patients with the serrated polyposis syndrome in the world. We will also define the small RNA transcriptome in 20 patients with sporadic sessile serrated, hyperplastic and adenomatous polyps to identify a unique panel of microRNAs (miRNAs) specific to sessile serrated polyps. The analysis of small RNAs will aid in differentiating between polyp types similar to previously published tumor classification studies using miRNA panels. We have already collected 10-20 colon and 5 serum samples in each cohort and will collect another 10 colon and 15 serum samples in each cohort during the first year of study. Based on previous power calculations we are confident 20 patients in each cohort will be adequate to define differential expression of miRNAs across polyp types. We will use leave-one-out cross-validation to develop a two-step procedure for defining small RNA gene signatures in patients with sessile serrated polyps and patients with traditional hyperplastic polyps. We will validate ten miRNAs uniquely expressed in patients with sessile serrated polyps by qPCR in tissue and serum samples from patients in each cohort. We will identify and validate select miRNA targets using transient co-transfection of mRNA 3' UTRs and miRNA expression plasmids, site-directed mutagenesis of mRNA 3' UTRs and western blotting of mRNA products. Our hypothesis is that this approach will identify molecular markers that accurately differentiate sessile serrated polyps, in both the serrated polyposis syndrome and sporadic patients, from other polyps and provide a non-invasive serum test for identifying patients with an increased risk for colon cancer. The objective is to stratify patient's risk for colon cancer to guide the frequeny of cancer screening tests and aid the design of chemoprevention trials.
Colon cancer remains a major health problem in the United States. Colon cancer may develop from sessile serrated colon polyps that are difficult to differentiate from hyperplastic polyps that have little or no risk of colon cancer. The goal of the proposed study is to discover tissue and blood based molecular diagnostics that identify patients with sessile serrated polyps that have a high likelihood of developing into colon cancer.
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