The early diagnosis, treatment and prevention of cancer recurrence are the major priorities in future oncology. An increasing number of cases are surgically cured as a result of early diagnosis and novel approaches to chemo and radiotherapy. However, a significant percentage of these patients will develop recurrent and/or metastatic disease. The prognosis for patients with metastatic breast, lung and colorectal cancers at diagnosis or as a cancer recurrence are poor. Thus, about fifty percent of high risk adenocarcinoma patients, dependent on tumor type and staging, will develop recurrent disease in 5 years. It is therefore hypothesized that improved adjuvant treatment will be of significant value for the treatment of minimal residual disease and prevention of cancer recurrence. Among the potential target antigens in lung, breast and colorectal cancers are: GA73-3 (EpCAM) antigen as defined by monoclonal antibody (MAb) CO17-1A, a blood group related oligosaccharide LewisY (LeY) defined by MAb BR55-2 and an Epithelial Growth Factor Receptor (EGFr) defined by MAb 425. All three MAb’s were the first murine antibodies shown to mediate ADCC with murine and human effector cells. Their IgG2a and IgG3 isotypes are highly active in CDC and ADCC and all effectively inhibit human tumor growth in xenografted nude mice. All three MAb’s were shown to be safe in a clinical setting. There is evidence that adjuvant immunotherapy in conventionally treated high risk patients can mediate micrometastatic tumor cell destruction and prevent adenocarcinoma recurrence. Passive immunotherapy may not be a sufficient approach to eradicate all tumor cells for extended periods of time. We are therefore also developing cancer vaccines based on the antigens defined by MAbs. The development of polypeptides that mimic oligosaccharides (LeY and LeX) is in the advanced stages. We expect that these molecules used as vaccines will induce not only humoral but also strong cellular responses in high risk cancer patients. To address and expedite the production of reliable and efficacious immunoproteins (antibodies and vaccines) modern, plant-based protein expression systems are used.