Most diseases, including human cancer, are frequently associated with an altered transcription pattern. The alteration of the transcriptome is not restricted to the production of aberrant levels of protein-coding RNAs, but also refers to the dysregulation of the expression of the multiple noncoding members that comprise the human genome. Unexpectedly, recent RNA-seq data of the human transcriptome have revealed that less than 2% of the genome encodes protein-coding transcripts, even though the vast majority of the genome is actively transcribed into non-coding RNAs (ncRNAs) under different conditions. In this review, we present an updated version of the mechanistic aspects of some long non-coding RNAs (lncRNAs) that play critical roles in human cancer. Most importantly, we focus on the interplay between lncRNAs and microRNAs, and the importance of such interactions during the tumorigenic process, providing new insight into the regulatory mechanisms underlying several ncRNA classes of importance in cancer, particularly transcribed ultraconserved regions (T-UCRs). This article is part of a Special Issue entitled: Clues to long noncoding RNA taxonomy1, edited by Dr. Tetsuro Hirose and Dr. Shinichi Nakagawa.