PSCA (Prostate Stem Cell antigen) is a cell surface antigen, which is overexpressed in ~40% of primary prostate cancers and in as many as 100% of metastatic ones. PSCA is also overexpressed in a majority of transitional cell and pancreatic carcinomas. Antibody directed against PSCA inhibits tumorigenesis, slows tumor growth, prolongs survival and prevents metastasis in a preclinical zenograft model indicating that PSCA may have utility as a prognostic marker and/or therapeutic target in prostate cancer.