The study was approved by the Institutional Review Board of the University of Utah. Study participants came from two population-based case–control studies that included all incident colon and rectal cancers between 30 and 79 years of age who resided along the Wasatch Front in Utah or were members of the Kaiser Permanente Medical Care Program (KPMCP) in Northern California. Participants were white, Hispanic or black for the colon cancer study (diagnosed between October 1991 and September 1994); the rectal cancer study (diagnosed between June 1997 and May 2001) also included Asians and American Indians not living on reservations (12 (link),13 (link)). Tumor tissue was obtained for 97% of all Utah cases diagnosed and for 85% of all KPMCP study participants (14 (link)).
Of the 2619 participants who were targeted for the study, we could not make miRNA on 637 because of too little tissue (Supplementary Table 1, available at Carcinogenesis Online). Both carcinoma and normal colonic mucosa (subsequently called normal) miRNA scans were obtained for 1657 individuals, carcinoma only miRNA scans for 297 participants, and normal only scans for 21 people. Both the carcinoma and normal tissue microarray failed for seven people. We targeted adenoma tissue for 388 individuals with carcinoma and obtained adenoma scans on 298 people. We could not make adenoma RNA for 84 adenomas and 6 microarrays failed. Since the study focuses on matched carcinoma–adenoma–normal samples, we excluded from analysis individuals whose microarray scan showed weak signal (i.e. 60 carcinomas, 80 normals and 2 adenomas) and those whose carcinoma could not be obtained (i.e. 59 individuals with normal tissue only when the carcinoma tissue microarray failed or did not pass QC and six individuals with adenoma only tissue when carcinoma tissue failed). After imputing normal miRNA (see Statistical methods for details) values for 354 individuals for those with only carcinoma tissue, we had a total of 1893 carcinoma/normal pairs and 290 individuals with carcinoma/adenoma/normal for analysis.