Because COX-2 accounted for 30% of VEGF from monolayer-cultured CT26 cells, and for 65% of VEGF from 3D-cultured CT26 cells, our results suggest that tumor-derived VEGF is mainly COX-2-dependent during 3D cancer cell growth at the avascular micrometastasis stage (Figure 3B). This evidence concerns the gene PTGS2 and cancer.