DEN Controller described potential conflict event when traffic on take off role was asked to cancel take off clearance but could not comply; creating a conflict with traffic making an unauthorized entry onto the same runway.

Narrative

I was working the Local Control 2 position at DEN Tower. I cleared Air Carrier Y for takeoff on Runway 17R. About 3/4 through his take off roll; I heard the Ground Controller key up and instruct Aircraft X (cargo) aircraft to stop! I looked at the runway and then to the Ground RADAR and Aircraft X Data Tag was on Runway 17R at the departure end. The ASDE-X/AMASS alerted to a potential collision and I canceled the takeoff clearance for Air Carrier Y. Air Carrier Y was close to V1 and seconds later rotated; then became airborne and stated that they were committed to take off at the point of cancellation. Perhaps better runway markings at the departure end of Runway 17R. This is a high use area and many small and large cargo aircraft utilize these taxiways during early morning and night time operations. I know the RED stop bars are only used during SMGCS operations (low visibility); but having these red bars on during normal operations at areas where aircraft do not 'Normally' enter the runway may have kept the aircraft from entering.