This paper presents a 40 GHz microwave biosensor used to monitor and characterize single cells (THP-1) subjected to electrochemotherapy and obtain an electronic signature of the treatment efficiency. This biosensor proposes a non-destructive and label-free technique that first allows, with the rapid measurement of single untreated cells in their culture medium, the extraction of two frequency-dependent dielectric parameters, the capacitance (C (f)) and the conductance (G (f)). Second, this technique can powerfully reveal the effects of a chemical membrane permeabilizing treatment (Saponin). At last, it permits us to detect, and predict, the potentiation of a molecule classically used in chemotherapy (Bleomycin) when combined with the application of electric pulses (principle of electrochemotherapy). Treatment-affected cells show a decrease in the capacitive and conductive contrasts, indicating damages at the cellular levels. Along with these results, classical biological tests are conducted. Statistical analysis points out a high correlation rate (R2>0.97), which clearly reveals the reliability and efficacy of our technique and makes it an attractive technique for biology related researches and personalized medicine.