AQP1 and neoplasm: Among the tumour stem cells, aqp9/18S was measured to 19.9 ± 6.35, whereas similar ratios for aqp1 and 4 were less, 0.02 ± 0.01 and 0.04 ± 0.18, respectively (mean ± SEM, n = 7, relative to aqp1 expression in tumour set to 1).