“…In addition, SOX2 and NANOG have been reported to maintain quiescence programs in DTCs/residual cancer cells and may contribute to metastatic relapse (Sosa et al 2015). Although SOX2, NANOG, OCT4, and KLF4 have been shown to increase metastasis of bladder cancer, breast cancer, lung cancer, and head and neck squamous carcinoma cells (Celia-Terrassa et al 2012;Vaira et al 2013;Lu et al 2014;Habu et al 2015), none of these factors has been specifically studied during metastasis initiation. Based on current knowledge, it is tempting to speculate that these factors may also facilitate metastatic initiation by promoting cell plasticity, adaptability, survival, and self-renewal as they do in primary tumors.…”