Evaluation of selected growth factor expression in canine spirocercosis (Spirocerca lupi)-associated non-neoplastic nodules and sarcomas

The study aims to assess the expression of vascular endothelial growth factor (VEGF)-A, fibroblast growth factor (FGF) and platelet-derived growth factor (PDGF) in the progression of the spirocercosis-induced oesophageal nodule in the dog from early, non-neoplastic, inflammatory nodule to sarcomatous neoplasia. Triplicate 4 μm-thick sections from 62 paraffin blocks containing Spirocerca-induced nodules were treated according to the steptavidin-biotin (LSAB) immunohistochemical method using polyclonal goat-anti-canine VEGF and anti-human FGF and PDGF antibodies. The nodules were classified as early inflammatory (n=15), pre-neoplastic (n=27) and neoplastic (n=20). Additionally, 10 sections of normal distal third of the oesophagus and 21 non-spirocercosis-related sarcomas were evaluated and compared with the Spirocerca-induced nodules. Five non-overlapping high power fields per case were evaluated under the light microscope and the fibroblasts were evaluated for percentage of labelled cells. The intensity of labelling was further classified as weak (score 1) or strong (score 2). The intensity score was multiplied by the percentage of labelled fibroblasts to yield a field score and the final score was obtained by calculating an average of the five fields. Antigen labelling was compared between the different histological grades and the controls using the Kruskal-Wallis test followed by the Mann-Whitney test for comparison between specific groups. The level of significance was set at 0.05. There were significant differences between the groups' score in all the growth factors that were examined. The normal oesophagus showed no labelling for any of the growth factors. FGF scored highest in the non-spirocercosis-related sarcoma group (median 118, 3-194) followed by the spirocercosis-induced sarcoma (34.5, 0-138), pre-neoplastic nodule (8, 0-99) and early nodule (0, 0-30) groups. All the differences among the groups were significant. VEGF scored highest in the non-spirocercosis-related sarcoma group (median 47, 1-110) followed by the spirocercosis-induced sarcoma (26, 0-136), pre-neoplastic nodule (0, 0-62) and early nodule (0, 0-35) groups. PDGF scored highest in the non-spirocercosis-related sarcoma group (median 29.2, 0-70) followed by the pre-neoplastic nodule (23.4, 0-95), early nodule (13.6, 0-132) and spirocercosis-induced sarcoma (0, 0-47) groups. The expression of VEGF and FGF increased as the nodule progressed from early inflammation to sarcoma, but it was not limited to spirocercosis-induced sarcomas. The expression of PDGF in spirocercosis was restricted to the early stages of nodule progression. Further investigation is warranted to establish whether FGF, VEGF or PDGF play a role in the pathogenesis of the malignant transformation in canine spirocercosis or are they simply integral to angiogenesis induction?