Overview of the tumor fluid validation assay.

A: Illustration of the principle for validation of tumor fluid as interstitial fluid. The concentrations of the extracellular markers, Na⁺ and creatinine were compared in isolated tumor fluid and plasma. When the isolated fluid derives solely from the interstitial space, the concentrations of the markers are equal to that in plasma, while addition of intracellular fluid will result in a lower tumor fluid:plasma ratio. To assess the presence of intracellular proteins, mass spectrometric analysis was used, the resulting protein lists were filtered based on known house keeping and extracellular proteins and the change in the number of spectra for intracellular proteins relative to albumin was used as an indicator of intracellular protein contamination. B: Measured tumor fluid:plasma ratio for creatinine and Na⁺ for tumor fluid (black) and frozen tumor fluid (grey). Values are mean ± SEM. *: Significantly different from tumor fluid (p<0.05) (Mann-Whitney test).