FGFR1 and neoplasm: On the other hand, we previously found that tumor immune resistance conferred by API5 is attributable to the upregulation of FGF2 and the activation of a downstream pathway involving FGFR1/PKCδ/ERK.18 In this study, FGF2 expression was increased in all of the above CSC-enriched conditions and it corresponded closely to API5 and NANOG expression (Figure 1).