Described herein are compositions and methods of use of anti-pancreatic cancer antibodies or fragments thereof, such as murine, chimeric, humanized or human PAM4 antibodies. The subject antibodies show a number of novel and useful therapeutic characteristics, such as binding with high specificity to pancreatic and other cancers, but not to normal or benign pancreatic tissues and binding to a high percentage of early stage pancreatic cancers. In preferred embodiments, the antibodies bind to pancreatic cancer mucins. The antibodies and fragments are of use for the detection, diagnosis and/or treatment of cancer, such as pancreatic cancer. The antibodies, such as PAM4 antibodies, bind to a PAM4 antigen that shows unique cell and tissue distributions compared with other known antibodies such as CA19.9, DUPAN2, SPAN1, Nd2, B72.3, and Lea and Le(y) antibodies that bind to the Lewis antigens.