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 antibodies show novel and useful diagnostic 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. Preferably, the antibodies bind to pancreatic cancer mucins such as MUC1 or MUC5ac and are of use for the detection and diagnosis of early stage pancreatic cancer. In more preferred embodiments, the anti-pancreatic cancer antibodies can be used for immunoassay of serum samples, wherein the immunoassay detects a marker for early stage pancreatic cancer in serum. Most preferably, the serum is extracted with an organic phase, such as butanol, before immunoassay. Alternatively, immunoassay with PAM4 and anti-CA19.9 antibodies may be utilized to improve sensitivity for pancreatic cancer.