The present invention relates to therapeutic ADCs comprising a drug attached to an anti-cancer antibody or antigen-binding antibody fragment. Preferably the drug is SN-38. More preferably the antibody or fragment thereof binds to Trop-2 and the therapy is used to treat a Trop-2 positive cancer. Most preferably the antibody is hRS7. The ADC is administered to a subject with a cancer in combination with an ABCG2 inhibitor. The combination therapy is effective to treat cancers that are resistant to drug alone and/or to ADC alone.
