Md. McGovern et al. from New York University School of Medicine published in the July 14th issue of PNAS their study results on a latent niche of a differentiated cell type which under certain conditions can promote either self-renewal, proliferation, or survival of stem cells that it inappropriately may contact. With C. elegans' germ-line stem cells, the investigators demonstrated that a latent niche drives stem cell proliferation through cell-cell interactions and thus, inappropriate Notch activation. It was also demonstrated that continuous Notch signaling is required for maintaining ectopic germ-line proliferation. The researchers propose from their experimental observations that this latent niche is distinguishable from the normal stem cell niche, premetastatic niche and ectopic niche. More importantly, this latent niche mechanism can initiate tumor formation without genetic changes in the tumor cell or tumor-initiating stem cell. The authors propose that "a latent niche mechanism may underlie tumorigenesis and metastasis in humans."