As shown by Muzza and co-workers [121], the whole intracellular DUOX and NOX4 activity is significantly higher in PTC cells than in normal thyroid cells, corroborating the upregulation of NOX4–p22phox (that is required for NOX4 catalytic activity to form a heterodimeric enzyme complex) in thyroid tumors, which might be related to a higher proliferation rate and tumor progression [122]. This evidence concerns the gene NOX4 and neoplasm.