IMMUNOHISTOCHEMICAL PHENOTYPING AND PCNA DETECTION IN GASTROINTESTINAL STROMAL TUMORS

The immunohistochemical profile and the expression of proliferating ce ll nuclear antigen (PCNA) were studied in a series of 44 mesenchymal t umors of the gastrointestinal tract (GIT). On routinely hematoxylin-eo sin stained sections 32 cases were classified as leiomyomas or leiomyo matoid tumors, 12 as leiomyosarcomas and I as a neurilemmoma. Immunohi stochemical stains for smooth muscle antigen (SMA), S-100 protein, gli al fibrillary acidic protein (GFAP), vimentin and desmin were performe d with the peroxidase-antiperoxidase method on paraffin sections. The streptavidin-biotin method for PCNA immunostaining was applied using t he monoclonal antibody PC 10. On the basis of immunohistochemical find ings, 32 cases were identified as leiomyomatoid tumors ol leiomyosarco mas (SMA positive, S-100 protein negative), 2 cases as nerve sheath tu mors (SMA negative, S-100 protein and GFAP positive), whereas 8 cases presented a mixed phenotype (SMA positive and S-100 protein positive). Two cases were negative for both SMA and S-1OO protein. All tumors sh owed positive immunostaining for vimentin and a negative one for desmi n. There was a con-elation between the histologic grade and proliferat ing score, displayed by PCNA expression in tumors of smooth muscle ori gin. The PCNA expression in tumors of mixed phenotype was intermediate to that seen in leiomyosarcomas (high expression) and in leiopmyomas (low expression).