Abstract
Introduction: :
Background: Pigmented intraocular tumors in dogs are different than humans, in particular regarding the frequency of each tumor type. Melanocytomas are noticeably more prevalent in dogs, representing the majority of tumors in this group. Clinically, melanocytomas and melanomas are indistinguishable in dogs. Even on histopathological grounds, the distinction between the two can often only be made by an experienced ocular pathologist.
Purpose: :
To evaluate the potential of a specific antibody panel to serve as diagnostic aids in canine pigmented intraocular tumors.
Methods: :
Nine samples of pigmented tumors were selected for this study: 4 melanocytomas, 4 melanomas (2 epithelioid and 2 mixed) and one adenocarcinoma of the ciliary epithelium. Samples were tested for the following markers: HMB-45, Melan-A, and NKI-C3. Immunohistochemistry was performed using the Ventana BenchMark (Ventana Medical Systems Inc, Tucson, AZ, USA) fully automated machine. Immunohistochemical expression was classified as negative, mild or strong. Sections of human skin melanoma were used as positive controls for all markers.
Results: :
The sections of skin melanoma were strongly positive for all 3 antibodies tested. Melan-A was positive in 3 melanocytomas (2 strong, 1 mild) and all melanomas (2 strong, 2 mild). HMB-45 was negative in all melanocytomas and positive in 2 melanomas (1 strong, 1 mild). NKI-C3 was negative in all specimens. The adenocarcinoma of the ciliary epithelium was negative for all markers.
Conclusions: :
We evaluated a panel of potential markers for canine pigmented intraocular lesions. Melan-A was the best marker for melanocytic differentiation, staining all melanomas and the majority of melanocytomas. NKI-C3 was not valuable for the diagnosis of melanocytic lesions in dogs. Given the preferential positivity of HMB-45 in melanomas, this marker may prove useful to differentiate malignant tumors from melanocytomas, which were all negative for HMB-45 in our sample. Further studies with a larger sample size are warranted to confirm these preliminary observations.
Keywords: melanoma • immunohistochemistry • melanocytes