Described herein are compositions and methods of use of antibody-drug conjugates (ADCs) comprising an anti-Trop-2 antibody or antigen-binding fragment thereof, conjugated to one or more cytotoxic drugs. Preferably, the antibody is an RS7, 162-46.2 or MAB650 antibody. More preferably, the antibody is humanized. Preferably the drug is SN-38, pro-2-pyrrolinodoxorubicin, paclitaxel, calichemicin, DM1, DM3, DM4, MMAE, MMAD or MMAF. The compositions and methods are of use to treat Trop-2 expressing cancers, such as breast, ovarian, cervical, endometrial, lung, prostate, colon, stomach, esophageal, bladder, renal, pancreatic, thyroid, epithelial or head-and-neck cancer. Preferably, the cancer is one that is resistant to one or more standard cancer therapies. More preferably, the anti-Trop-2 antibody binds to Trop-2 expressed on normal cells, but administration of the anti-Trop-2 ADC to human cancer patients at a therapeutically effective dosage produces only limited toxicity.
