Twenty-one consecutive cases of gastrointestinal spindle cell stromal
tumors (SCSTs) were studied histologically and immunohistochemically. They consisted of 18
smooth muscle tumors, 2
neurilemmomas (
schwannomas), and 1 unclassified malignant
tumor designated as stromal
sarcoma. Slender, spindle and wavy nuclei with palisading associated with peripheral
tumor aggregation of lymphocytes are the pathological hallmarks of
neurilemmoma. With
peroxidase-antiperoxidase method,
antibodies to
Glial Fibrillary Acidic Protein (GFAP), Leu-7, S-100,
desmin and HHF35 were applied.
Antibodies to Leu-7 and GFAP could only be demonstrated in
neurilemmomas (2 cases). Antibody to S-100 was observed strongly in 2
neurilemmomas and 1 stromal
sarcoma, and focally in a
leiomyoma, while the other SCSTs were negative. One
neurilemmoma disclosed focal positivity of
desmin. Six of 10
leiomyomas revealed varied degrees of positive staining of
desmin and HHF35. One
epithelioid leiomyoma, two
leiomyosarcomas and five
smooth muscle tumors of undetermined malignant potential (STUMP) disclosed no immunoreactivity. The study suggests that panel of immunostaining should be applied. Coexpression of GFAP, Leu-7 and S-100 as well as negative staining of HHF35 is characteristic of
neurilemmoma. On the contrary, coexpression of
desmin and HHF35 while negative for GFAP, S-100 and Leu-7 are suggestive of
smooth muscle tumor. In poorly differentiated SCST, histological features and immunostains are always disappointing. Diagnosis of those
tumors as stromal
tumor is more appropriate or electron microscopic observation should be included for accurate classification.