TP53 and cancer: Stem cell altruism is a fitness-defending mechanism that defends/protects neighboring stem cells with low fitness. Altruistic stem cells acquire a “super-fit” state by down regulating p53, and secrete factors to increase the fitness of its own members, and then self-sacrifice by undergoing spontaneous apoptosis/differentiation (Das et al., 2012). The mechanism could play important role in tissue regeneration, as well as genesis of cancer (Das, 2014; Di Gregorio et al., 2016). Stem cell altruism could be better understood in context of stem cell competition.