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The transfer impedance measured by a tetrapolar probe has been widely used to detect tumors located in the skin. The main drawback of this method is that its sensitivity is highly dependent on the electrode geometry probe. In this article, the impedance method is used to calculate the sensitivity for transfer impedance measurement by simulating two different medium: a sample of homogeneous tissue; and a sample of tissue with a skin tumor inside. The sensitivity of the transfer impedance measurements was investigated taking into account different electrodes diameters and different separations between drive and receive electrodes. The impedance method was modified and it is proposed a new numeric solution based on the interpolation of the electrical potential inside the tissue sample under study. The results from simulations showed that the sensitivity to measure the potential change on the tissue surface is highly dependent on the electrode diameter and the separation between drive and receive electrode pairs. The maximum sensitivity was 10% for an electrode diameter of 1 mm and 2.5 mm of separation, also the measured transfer impedance was approximately 4% of the total load impedance in the drive electrode site. It can be concluded that the measured transfer impedance can be increased by decreasing either the electrode diameter or the electrode separation. The results may be important when implementing an impedance probe for tissue characterization.