A large number of tiny noncoding RNAs have been cloned and named microRNAs (miRs). Recently, we have reported that miR-15a and miR-16a, located at 13q14, are frequently deleted and͞or down-regulated in patients with B cell chronic lymphocytic leukemia, a disorder characterized by increased survival. To further investigate the possible involvement of miRs in human cancers on a genome-wide basis, we have mapped 186 miRs and compared their location to the location of previous reported nonrandom genetic alterations. Here, we show that miR genes are frequently located at fragile sites, as well as in minimal regions of loss of heterozygosity, minimal regions of amplification (minimal amplicons), or common breakpoint regions. Overall, 98 of 186 (52.5%) of miR genes are in cancer-associated genomic regions or in fragile sites. Moreover, by Northern blotting, we have shown that several miRs located in deleted regions have low levels of expression in cancer samples. These data provide a catalog of miR genes that may have roles in cancer and argue that the full complement of miRs in a genome may be extensively involved in cancers.

Prognostic markers that can predict the relapse of localized non-small cell lung cancer (NSCLC) have yet to be defined. We surveyed expression profiles of microRNA (miRNA) in stage I NSCLC to identify patterns that might predict recurrence after surgical resection of this common deadly cancer. Small RNAs extracted from formalin-fixed and paraffin-embedded tissues were hybridized to locked nucleic acid probes against 752 human miRNAs (representing 82% of the miRNAs in the miRBase 13.0 database) to obtain expression profiles for 37 cases with recurrence and 40 cases without recurrence (with clinical follow-up for at least 32 months). Differential expression between the two case groups was detected for 49% of the miRNAs (Wilcoxon rank sum test; P < 0.01). The performance of expression profiles at differentiating the two case groups was assessed by leave-one-out and Monte Carlo cross-validations. In leave-one-out cross-validation using support vector machines-or top-scoring gene pair classifier methods, which looked for six-or two-miRNA-based classifiers, the identified miRNA expression pattern predicted recurrence with an accuracy of 70% and 83%, and hazard ratio of 3.6 [95% confidence interval (95% CI), 1.8-7.1] and 9.0 (95% CI, 4.4-18.2), respectively. Mean accuracy in Monte Carlo cross-validation using 1,000 random 60-17 splits was 69% (95% CI, 68-70) and 72% (95% CI, 71-72), respectively. The specific miRNAs mir-200b*, mir-30c-1*, mir-510, mir-630, mir-657, and mir146b-3p and mir-124*, mir-585, and mir-708, respectively, represented most commonly among the 1,000 classifiers identified in Monte Carlo cross-validation by the two methods. MiRNAs mir-488, mir-503, and mir-647 were identified as potential reference miRNAs for future studies, based on the stability of their expression patterns across the 77 cases and the two case-groups. Our findings reinforce efforts to profile miRNA expression patterns for better prognostication of stage I NSCLC. Cancer Res; 70(1); 36-45. ©2010 AACR.