Dormant disseminated cancer cells, arrested and nonproliferating, are "good" cancer cells because there is no need to worry unless they resume growth. The mechanisms by which dormant disseminated cancer cells are put to sleep at distant sites and re-awakened are poorly understood. Moreover, it is not clear whether re-awakened cancer cells have a role in disease courses. Cyrus Ghajar and colleagues identified a mechanism of dormancy and growth resumption that might become important when more closely linked to clinical reality.