Phosphatase and tensin homolog (PTEN) is a tumor-suppressor gene. PTEN 
pseudogene (PTENp) acts as an endogenous RNA, which regulates its parental gene 
by competitively binding to the 3' UTR of PTEN gene in the human. Despite the 
importance of this pseudogene, little is known about the molecular evolution of 
PTENp in mammals. In this study, we identified 37 pseudogenes from 65 mammalian 
genomes. Among them, 32 were from rodents or primates. Phylogenetic analyse 
showed a complex evolutionary history of this gene family. Some PTENps were 
shared both in primates and rodents. However, some PTENps were shown to be 
species-specific, such as the tasmanian devil PTENp1, nine banded armadillo 
PTENp1 and gibbon PTENp1. Most interestingly, the naked mole rat (NMR), an 
anticancer model organism, possessed 17 copies of PTENps, which were classified 
into four clades based on the phylogenetic analyses. Furthermore, we found that 
all the 3'UTR of PTEN and PTENps shared common microRNA (MicroRNA) binding sites 
in NMR, based on our prediction of specific MicroRNA binding sites. Our findings 
suggested that multiple gene duplications have occurred in the formation of 
PTEN/PTENp gene family during the evolution of mammals. Some PTENps were 
relatively ancient and were shared by primates and rodents; others were newly 
originated through species- specific gene duplications. PTENps in NMR may 
function as competitive endogenous RNAs (ceRNAs) to regulate their counterpart 
genes by competing for common MicroRNAs, which may be one of the interpretations 
for the cancer resistance in NMR.