Immunohistochemical phenotyping and PCNA detection in gastrointestinal stromal tumors.

The immunohistochemical profile and the expression of proliferating cell nuclear antigen (PCNA) were studied in a series of 44 mesenchymal tumors of the gastrointestinal tract (GIT). On routinely hematoxylin-eosin stained sections 31 cases were classified as leiomyomas or leiomyomatoid tumors, 12 as leiomyosarcomas and 1 as a neurilemmoma. Immunohistochemical stains for smooth muscle antigen (SMA), S-100 protein, glial fibrillary acidic protein (GFAP), vimentin and desmin were performed with the peroxidase-antiperoxidase method on paraffin sections. The streptavidin-biotin method for PCNA immunostaining was applied using the monoclonal antibody PC 10. On the basis of immunohistochemical findings, 32 cases were identified as leiomyomatoid tumors or leiomyosarcomas (SMA positive, S-100 protein negative), 2 cases as nerve sheath tumors (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-100 protein. All tumors showed positive immunostaining for vimentin and a negative one for desmin. There was a correlation between the histologic grade and proliferating score, displayed by PCNA expression in tumors of smooth muscle origin. The PCNA expression in tumors of mixed phenotype was intermediate to that seen in leiomyosarcomas (high expression) and in leiomyomas (low expression).