LTA4H and FXR1 Gene and Protein Expression in Canine Oral Melanoma

Introduction: Canine oral melanoma is a common neoplasm that is usually considered malignant, although the correlation between histology and prognosis is still controversial. Therefore, research of new biological markers is ongoing. In this study, LTA4H (an enzyme of the arachidonic acid cascade) and FXR1 (a RNA binding protein) are investigated. Both have been investigated previously for their possible role in metastasis of ocular melanoma, and are studied here in canine oral melanoma. Materials and Methods: Twenty-nine samples of formalin-fixed and paraffin wax-embedded canine oral melanomas were analyzed. Routine HE sections were evaluated on light microscopy and received a histological description, including mitotic activity index (MI). Immunohistochemistry (IHC) for LTA4H, FXR1 and Ki67 was performed. LTA4H and FXR1 were scored semiquantitatively and Ki67 was scored quantitatively. The expression of LTA4H and FXR1 genes was also quantified by RT-PCR. Results: Most of the cases were epithelioid, poorly pigmented melanomas. MI ranged from 0.1 to 9.2 (median 1.1). Ki67 index ranged from 7.9 to 44.4% (median 19%). IHC was positive in 29/29 LTA4H and 28/29 FXR1, with variable intensity and percentage of positivity. RT-PCR relative expression values ranged from 0.49 to 9.11 for LTA4H and 0.15 to 10.33 for FXR1 (in four cases was under the detection limit). Conclusions: LTA4H and FXR1 were detected in all tested melanomas. Marked differences between cases were noted with RT-PCR, although target gene expression levels were not consistent with histological parameters or Ki67 index. Conversely, immunohistochemical positivity was elevated in most cases with negligible expression differences. Further work is ongoing to clarify the prognostic significance of different levels of expression.