Immunohistochemical Diagnosis of Canine Oral Amelanotic Melanocytic Neoplasms

Abstract

Definitive diagnosis of canine oral melanocytic neoplasms is often difficult because of variability in pigmentation and cellular pleomorphism. These neoplasms can resemble carcinomas, sarcomas, and round cell neoplasms, which differ in prognosis and treatment. A variety of immunohistochemical antibodies have been used for diagnosis of melanocytic neoplasms in humans and dogs; however, sensitivity and specificity of many markers have not been determined in amelanotic melanocytic neoplasms in dogs. The authors investigated a comprehensive panel of immunohistochemical markers in 49 canine oral amelanotic melanocytic neoplasms-namely, Melan-A, PNL2, HMB-45, microphthalmia transcription factor (MiTF), S-100, tyrosine hydroxylase, tyrosinase, tyrosinase-related proteins 1 and 2 (TRP-1 and TRP-2), and CD34. Ten well-differentiated cutaneous soft tissue spindle cell sarcomas were negative controls. Melan-A, PNL2, TRP-1, and TRP-2 were highly sensitive and 100% specific for the diagnosis of canine oral amelanotic melanocytic neoplasms. S-100 and MiTF showed high sensitivity but were less specific; that is, they also labeled a proportion of the soft tissue spindle cell sarcomas. HMB-45, tyrosinase, and tyrosine hydroxylase were 100% specific but had low sensitivities. CD34 did not label any of the melanocytic neoplasms but did label 80% of the soft tissue spindle cell sarcomas. A cost-effective and efficient immunodiagnostic cocktail containing antibodies against PNL2, Melan-A, TRP-1, and TRP-2 was created that had 100% specificity and 93.9% sensitivity in identifying canine oral amelanotic melanocytic neoplasms. The spindloid variant was the variant with the lowest sensitivity to the cocktail. The likelihood of correctly diagnosing canine oral amelanotic melanocytic neoplasms was dramatically higher when biopsy samples contained ample overlying and adjacent epithelium.

Immunohistochemical Expression of Melanocytic Antigen PNL2, Melan A, S100, and PGP 9.5 in Equine Melanocytic Neoplasms

“…10 Melan A is one of the most commonly used melanocytic differentiation markers for human and canine melanomas. 6,14,24 In this study, Melan A was not expressed in any of the equine melanocytic tumors or in normal melanocytes of equine skin, although expression of Melan A has been reported in an equine melanocytic tumor and in equine melanocytic cell cultures. 3,25 Immunoreactivity of Melan A was not evaluated in nonmelanocytic equine tumors in those studies.…”

“…13 Melan A expression in 1 equine melanocytic neoplasm and melanocytic cell lines has been reported. 3,25 PNL2 is a monoclonal antibody that recognizes a fixativeresistant melanocytic antigen in humans, dogs, and some laboratory animals, 2,7,8,16,18,24 the exact structure of which has yet to be identified. 10 In humans, PNL2 also labels angiomyolipomas and mature myeloid cells, including neutrophils, but not other nonmelanocytic tumors, including various carcinomas and sarcomas.…”

Comparison of CD34, CD31, and Factor VIII–Related Antigen Immunohistochemical Expression in Feline Vascular Neoplasms and CD34 Expression in Feline Nonvascular Neoplasms

“…CD34-positive melanomas have been occasionally reported in humans, 2 although CD34 immunoreactivity was not observed in a recent evaluation of the immunohistochemical phenotype of canine oral melanoma. 25 The difficulty in evaluating the immunoreactivity of the nonvascular neoplasms is in interpreting the specificity of the CD34 immunolabeling. Polyclonal antibodies are considered to be more sensitive markers because of recognition of multiple epitopes.…”

Melanoma amelanótico oral en perro joven: Reporte de un caso

“…Desta forma são necessários exames histológicos associados algumas vezes aos ensaios de imunohistoquímica para um diagnóstico mais preciso (Smedley et al, 2011). No presente trabalho, não foi necessário a realização de imunohistoquímica sendo, o diagnóstico confirmado como melanoma amelanótico.…”