There are disclosed methods and compositions for the diagnosis, prevention, and treatment of tumors and cancers in mammals, for example, humans, utilizing the CTSZ and CD24 genes, which are amplified colon cancer and/or ovarian cancer and/or breast cancer genes. The CTSZ and CD24 genes, their expressed protein products and antibodies are used diagnostically or as targets for cancer therapy or vaccine; they also are used to identify compounds and reagents useful in cancer diagnosis, prevention, and therapy.