There is disclosed an initial identification of an N-terminally truncated HER-2/neu product. This product is a 95 kDa polypeptide having in vitro kinase activity (as determined by western blotting). Moreover, immunoprecipitations using domain specific antibodies was able to utilize this specific polypeptide from intracellular fragments as a diagnostic and prognostic indicator of adenomacarcinomas without the severe dilution effects encountered by measuring ECD.