DUOX1 and neoplasm: In contrast, removing extracellular ROS by UAS-Duox RNAi or overexpression of the UAS-hCatS transgene which encodes a secreted human catalase (Ha et al., 2005b2005; Ha et al., 2005a), strongly suppressed tumor growth of scrib−/−RasV12 mutant cells (Figure 1J,K) suggesting that extracellular ROS are required for tumor growth.