Conventional in-vitro monitoring of cancer tissues is time-consuming and has limited accessibility. To enable a non-invasive technique to observe tumor behavior, Electrical Impedance Spectroscopy (EIS) can be employed. EIS may be performed by Two Electrode-Technique (2-ET), where both electrodes are used for excitation and recording purposes, or by Four Electrode-Technique (4-ET), where the two outer electrodes are used for current excitation, and the two inner electrodes record the resulting signal.1 Here, we successfully used both techniques to monitor the tumor adhesion and evaluate therapeutic interventions. Three-dimensional Tumor Spheroids (3D-TS; diameter ~300 µm) made of human colon cancer cells were cultured on a Microelectrode Array (MEA; pitch: 70 µm). Control and drug treatment experiments (Ncontrol =14, Ndrug =10) were conducted using EIS to observe 3D-TS changes. Measurements were performed at 4h, 21h, and 66h after interfacing the 3D-TS with the MEA. EIS allows for reliable, noninvasive identification of adherent spheroids. The identification was confirmed using optical microscopy. With both techniques (2-ET and 4-ET), we obtained significantly higher impedance amplitudes for electrodes underneath the tumor spheroids than for bare electrodes. During the drug treatment, EIS revealed a decrease in the impedance over time compared to the control groups. In the future, we plan to interface and record spheroids on flexible MEA. 1. Bragos, R. et al.”, Four Versus Two-Electrode Measurement Strategies for Cell Growing and Differentiation Monitoring Using Electrical Impedance Spectroscopy,” IEEE EMBS. pp:2106-2109, 2006.