Microwave ablation (MWA) is a promising treatment option for patients suffering from liver cancer utilizing electromagnetic wave heating within the targeted tissue at microwave frequencies. Knowledge about the dielectric properties of the targeted tissues is essential for the design of recent MWA systems by including treatment monitoring possibilities. This work focuses on the evaluation of the patient-specific dielectric contrast between healthy and diseased liver parts at discrete frequencies at 2.45 GHz and 5.8 GHz, as well as a broadband data analysis. Measurements yield a frequency-dependent dielectric contrast with local maxima for each patient. Due to large variations between the dielectric properties of the patients, the need for individual thresholds can be derived to distinguish between healthy and malignant tissue.