However, when trying to correlate it with blood flow markers, no statistically significant association was found between F-EF5 and the perfusion tracer 15O-H2O. HNC cell lines showed a very good correlation between CA-IX/HIF-1α expression and F-EF5 uptake, demonstrating the tracer affinity not only towards more hypoxic tumours but also towards an adverse, more aggressive phenotype [19]. Here, HIF1A is linked to neoplasm.