SOX2 and melanoma: Despite being distinct from principal tumor cells, several characteristics of LNM cells suggest they play a role in tumor formation and growth—for example, the importance of Sox2, which is most strongly expressed in LNM cells (Fig. 3c), in tumor formation (Fig. 3e); the persistence of LNM cells during serial transplantation (Fig. 3a–d); and the expression within LNM cells of gene signatures associated with human and mouse melanoma cell states (Fig. 4c, Fig. S8E).