The invention provides isolated anti-ovarian, pancreatic, lung or breast cancer antigen (Pro104) antibodies that bind to Pro104 on a mammalian cell in vivo. The invention also encompasses compositions comprising an anti-Pro104 antibody and a carrier. These compositions can be provided in an article of manufacture or a kit. Another aspect of the invention is an isolated nucleic acid encoding an anti-Pro104 antibody, as well as an expression vector comprising the isolated nucleic acid. Also provided are cells that produce the anti-Pro104 antibodies. The invention encompasses a method of producing the anti-Pro104 antibodies. Other aspects of the invention are a method of killing a Pro104-expressing cancer cell, comprising contacting the cancer cell with an anti-Pro104 antibody and a method of alleviating or treating a Pro104-expressing cancer in a mammal, comprising administering a therapeutically effective amount of the anti-Pro104 antibody to the mammal.