HIF1A and fibrosarcoma: To this end, we injected isogenic VEGF-deficient fibrosarcoma cells (VEGF null)6, representing a model with low VEGF bioavailability (Supplementary Fig. 7a) within the tumour and the matching VEGF-expressing WT fibrosarcomas6 (high VEGF bioavailability) (Supplementary Fig. 7a) subcutaneously into WT and HIF-1α KO mice (Fig. 7a).