The phenotype of the proliferated spindled cells and the histogenesis
of inflammatory fibroid polyp (IFP) have been a matter of debate, To c
larify the immunohistochemical profile of the main cellular component,
we reviewed histologically and studied immunohistochemically 11 cases
(12 lesions) of IFP of the stomach, The lesions ranged in size from 0
.4 to 3.0 cm (mean, 1.0 cm), All of the IFPs occurred in the antrum, S
even cases (63.6%) were accompanied by carcinoma or adenoma, which in
two cases was present in covering epithelium, Grossly, eight IFPs were
sessile, and four were polypoid, Microscopically, seven (58.3%) occup
ied both the mucosa and submucosa Four (33.3%) were confined to the mu
cosa, and one was localized only in the submucosa They were characteri
zed by proliferation of relatively uniform spindled cells, often in a
whorl-like arrangement around the blood vessels and glands, Eosinophil
ic and lymphocytic infiltration of varying degree was always present,
The spindled cells in all of the IFPs were diffusely immunoreactive fo
r vimentin and CD34. Seven (58.3%) were focally positive for histiocyt
ic markers, such as KP1 and HAM56, Three (25%) showed focal immunoreac
tivity for alpha smooth muscle actin. Cytokeratin, desmin, S100 protei
n, Factor VIII RAG, and Ki-67 were negative in these spindled cells. T
he principle proliferating cells in IFPs in this study showed variable
degrees of histiocytic and myofibroblastic lines of differentiation.
Under the influence of some etiologic factors, the primitive, uncommit
ted spindled mesenchymal cells exhibiting CD34 immunoreactivity around
the blood vessels and glands in the lower portion of mucosa and submu
cosa might play a role in development of IFP.