By specifically depleting Apelin expression in tumor epithelial cells (Apln+/+;E0771 shApln) or the cells of the tumor microenvironment (Apln−/−;E0771 shRen), we could investigate the importance of these two sources of Apelin for the observed growth decrease in fully Apelin‐depleted tumors (Apln−/−;E0771 shApln). Here, APLN is linked to neoplasm.