Screening drugs on biopsies from cancer patients can promote precision medicine, but is challenging due to limited tumor samples for cancer patients (especially at an early stage). With the advantage of small samples needed, digital microfluidics (DMF) emerged to be very prominent platform for drug screening. In this paper, a DMF platform was developed, for drug screening of primary biopsy samples from xenograft mouse breast cancer models. The on-chip individual mouse drug screening results matched well with the individual in-vivo tumor response, suggesting the effectiveness for rapid determination of the optimal effective drug for personalized cancer therapies based on DMF platform.