The most notable observation, however, is the differences between epithelial and stromal tumor tissue; whilst there are no significant differences between any of the aquaporin transcripts in normal breast tissue; AQP1, AQP8, AQP4, AQP6 and AQP9 are all significantly higher in stromal tumor tissue, implying a considerable change in cellular phenotype. This evidence concerns the gene AQP9 and neoplasm.