ZEB1 and melanoma: Multiple intermediate states would thus support melanoma progression across different tumor microenvironments, from primary tumors in an invasive phase characterized by MITFlow, a high ZEB1/ZEB2 ratio, and SNAIL1 expression, to metastatic colonization and outgrowth with MITFhigh, a low ZEB1/ZEB2 ratio, and SNAIL2 expression [12].