During recent years, novel approaches and new technologies have revealed a 
startling level of complexity of higher eukaryotes' transcriptome. A large 
proportion of the transcriptional output is represented by protein noncoding 
RNAs (ncRNAs) that arise from the "dark matter" of the genome. Focus on such 
sequences has revealed numerous RNA subtypes with several functions in RNA 
processing and gene expression regulation, and deep sequencing studies imply 
that many remain to be discovered. This review gives a picture of the state of 
the art of a novel class of long ncRNA known as transcribed-ultraconserved 
regions (T-UCRs). Most recent studies show that they are significantly altered 
in adult chronic lymphocytic leukemias, carcinomas, and pediatric 
neuroblastomas, leading to the hypothesis that UCRs may play a role in 
tumorigenesis and promising innovative future T-UCR-based therapeutic 
approaches.