The present invention relates to a method for producing patient specific anti-cancer antibodies using a novel paradigm of screening. By segregating the anti-cancer antibodies using cancer cell cytotoxicity as an end point, the process makes possible the production of anti-cancer antibodies customized for the individual patient that can be used for therapeutic and diagnostic purposes. The invention further relates to the process by which the antibodies are made and to their methods of use. The antibodies can be made specifically for one tumor derived from a particular patient and are selected on the basis of their cancer cell cytotoxicity and simultaneous lack of toxicity for non-cancerous cells.