AQP9 and breast cancer: However, since all three aquaglyceroporins are expressed in the same cells, and several peroxiporins are expressed in breast cancer (AQP1 [4,5], AQP3 [6] AQP5 [7] and AQP9 [11] as well as AQP7 (AQP7 knockdown in breast cancer cells resulted in decreased oxidative stress tolerance [13])), targeted intervention strategies of only one AQP may encounter compensatory mechanisms.