ID1 and esophageal squamous cell carcinoma: With respect to functional effects, we found that treatment with conditioned medium from Id1-overexpressing ESCC cells for 24 h induced the migration (Fig. 1g) but not the proliferation (Supplementary Fig. 1f) of fibroblasts, and that the effect was attenuated by IGF2 knockdown in cancer cells, or addition of IGF2-neutralizing antibody to the conditioned medium.