Several studies have shown that 
metastatic cancer cells may lie dormant in a 
secondary site for more than a decade, all the while 
retaining the ability to aggressively reemerge. Once 
these dormant cancer cells regrow, cancer becomes 
incurable, yet the mechanisms that instruct 
metastatic cancer cells to become dormant and later 
escape from dormancy still remain unknown. In this 
review we will discuss the known regulatory roles 
of the microenvironment in tumor dormancy and 
some potential models for future studies of tumor 
dormancy. Better understanding of the mechanisms 
involved has the potential to lead to significant 
improvements in the care of advanced cancer 
patients and the prevention of cancer recurrence.