A scanning apparatus, is used to effect multiple images of a tumor in which a contrast agent has been localized as a detectable marker over a selected time to map the change in the imaged marker. The rate of change in the imaged marker and/or contrast intensity of the dyed tissues is used to assess tumor aggressiveness and as an early predictor of response to cancer therapy. In particular, following the marking of tumor or cancerous tissues by the initial localization of an imageable contrast agent, the rate of change in the volume and/or area of the imaged marker is used to provide an indication of tumor interstitial fluid pressure (TIFP).