Melanoma is relatively common in dogs. The most frequently affected sites are the oral cavity, skin, digit, and the eye. Cutaneous and intraocular melanomas are mostly benign and slowly growing. They rarely metastasize. In contrast, oral melanoma, subungual melanoma and extrabulbar melanoma are virtually always considered malignant. Thus, the biological behavior of the canine melanoma varies with location.
Different expression or overexpression of various growth factors and their receptors could be a reason for tumor proliferation, vascularization, and metastasis.
Aim of the present study was to evaluate the expression of the growth factor receptors EGFR and KIT as well as the expression of the growth factor VEGF in canine melanoma. Further, the prognostic potential of these growth factors as well as their possible role as therapeutic target should be evaluated.
In the present study, EGFR expression was detected by immunohistochemistry in oral, cutaneous and uveal canine melanoma.
Additionally, a correlation between EGFR expression and cell type, as well as a tendentious difference in cutaneous melanoma between heavily and weakly pigmented cells was observed. However, a correlation between expression and malignancy was not found.
Furthermore, the growth factor receptor KIT was detected immunohistochemically in canine melanoma. No correlation between KIT expression and histological criteria of malignancy as well as survival was found, though.
The growth factor VEGF was detected in canine melanoma assessed by immunostaining. A significant correlation between malignancy and VEGF expression was observed, thus suggesting a possible role of VEGF in carcinogenesis and tumor progession in dogs. Moreover, correlations between cell type and VEGF expression as well as between degree of pigmentation and VEGF expression were found.
In summary, the present study detected expression of EGFR, KIT and VEGF immunohistochemically in canine melanoma. VEGF may have prognostic importance not only for human melanoma but also for canine melanoma.
Further studies should examine these growth factors as therapeutic targets in the treatment of the canine melanoma.