Immunostaining with HAM56 in the diagnosis of adenocarcinomas.

Data has been presented suggesting that the monoclonal antibody HAM56 reacts with many adenocarcinomas but not with colonic adenocarcinomas. Previous studies have suggested that immunostaining with HAM56 may be useful in the differential diagnosis of adenocarcinoma of unknown origin. To test the specificity of HAM56 immunostaining in the diagnosis of adenocarcinomas, we studied formalin-fixed, paraffin-embedded tissue from 213 adenocarcinomas from a variety of sites using an avidin-biotin immunohistochemical technique. Positive reactivity was seen in some tumors of all types including 39% of colonic adenocarcinomas. We conclude that immunostaining with HAM56 is not specific in the differential diagnosis of adenocarcinoma of unknown origin.