NRP1 and neoplasm: Deletion of Sox2 causes cSCC tumour regression and malignant transformation.20 Sox2 expression regulates the Nrp1 and vascular endothelial growth factor (VEGF) pathway, which causes cSCC proliferation by facilitating tumour‐initiating cells to generate more undifferentiated tumour cells.21 The current study sought to explore the role of C3a in cSCC and its association with Sox2.