CAT and neoplasm: The validity and significance of this experimental system has been explicitely shown for mixtures of untreated tumor cells with increasing percentages of tumor cells that had been either pretreated by siRNA-mediated knockdown of their protective catalase95, inactivation of their protective catalase through 1O2 generated by an illuminated photosensitizer96, or by defined sources of H2O2 and NO2− 60.