PKD1 and neoplasm: Given the critical role of ECs in arteriolar differentiation and tumor progression [15,16,17,83,84,85], vascular ECs in highly vascularized pNETs may nurture CSCs by direct EC-CSC interactions and by indirect generation of such vascular niche factors as LPA to activate PKD1 signaling [4,16,17,24,28], thereby, leading to progression toward malignancy, drug resistance and metastasis.