Sections from 35
formalin-fixed,
paraffin-embedded, canine
gastrointestinal stromal tumors consisting of 14
leiomyomas (five stomach, three small intestine, two colon, four rectum), 18
leiomyosarcomas (one stomach, five small intestine, nine cecum, three rectum), two undifferentiated
sarcomas (two stomach), and one
neurofibrosarcoma (small intestine) were examined for the expression of
vimentin,
S-100 protein, alpha-smooth muscle actin, and
desmin via immunoperoxidase methodology using an
avidin-
biotin complex technique. The
leiomyomas were 4/14 (29%)
vimentin-positive, 3/14 (21%)
S-100 protein-positive, 10/14 (71%) alpha-smooth muscle actin-positive and 13/14 (93%)
desmin-positive.
Leiomyosarcomas were 18/18 (100%)
vimentin-positive, 11/18 (61%)
S-100 protein-positive, 9/18 (50%) a-smooth muscle actin-positive, and 15/18 (83%)
desmin-positive. The undifferentiated
sarcomas were 2/2 (100%)
vimentin-positive, 2/2 (100%)
S-100 protein-positive, 1/2 (50%) alpha-smooth muscle actin-positive, and 0/2 (0%)
desmin-positive. The
neurofibrosarcoma was
vimentin and
S-100 protein-positive and alpha-smooth muscle actin- and
desmin-negative. Thirty-one of thirty-five (89%) of all
neoplasms demonstrated reactivity for either
desmin and/or alpha-smooth muscle actin.
S-100 protein reactivity occurred in 17/35 (49%) of all specimens. Lack of
desmin and alpha-smooth muscle actin reactivity occurred in 4/35 (11%) of all specimens, all of which were
vimentin-positive. The immunohistochemical results indicate that the majority of canine
gastrointestinal stromal tumors (GIST) with light microscopic features of smooth muscle cells have immunohistochemical staining patterns supporting smooth muscle differentiation.
Vimentin reactivity correlated with a light microscopic diagnosis of
malignancy. The lack of smooth muscle cell markers in some
tumors and the high percentage of cases positive for
S-100 protein may suggest a more complex histogenesis or differentiation for subgroups of these
tumors.