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 diagnostic characteristics, such as binding with high specificity to pancreatic and other cancers, but not to normal 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 and diagnosis of early stage pancreatic cancer. In preferred embodiments, the anti-pancreatic cancer antibodies can be used for immunoassay of serum samples, wherein the immunoassay can detect a marker for early stage pancreatic cancer in serum. More preferably, the serum is extracted with an organic phase, such as butanol, before immunoassay.