Long non-coding RNAs (lncRNAs) are transcripts longer than 200 bp with no 
protein-coding capacity. Transcribed ultraconserved regions (T-UCRs) are a type 
of lncRNA and are conserved among human, chick, dog, mouse and rat genomes. 
These sequences are involved in cancer biology and tumourigenesis. Nevertheless, 
the clinical significance and biological mechanism of T-UCRs in breast cancer 
remain largely unknown. The expression of uc.38, a T-UCR, was down-regulated in 
both breast cancer tissues and breast cancer cell lines. However, uc.38 was 
expressed at significantly lower levels in larger tumours and tumours of more 
advanced stages. Based on the results of in vitro and in vivo experiments, 
up-regulation of uc.38 expression inhibited cell proliferation and induced cell 
apoptosis. Thus, uc.38 suppressed breast cancer. Additional experiments revealed 
that uc.38 negatively regulated the expression of the pre-B-cell leukaemia 
homeobox 1 (PBX1) protein and subsequently affected the expression of Bcl-2 
family members, ultimately inducing breast cancer cell apoptosis. Describing the 
uc.38/PBX1 axis has improved our understanding of the molecular mechanisms 
involved in breast cancer apoptosis and has suggested that this axis is a 
potential therapeutic target for breast cancer.