Use of histochemical techniques for accurate diagnosis of melanocytic neoplasms in dogs

Abstract

Abstract Cutaneous and oral melanocytic neoplasms of dogs have several histomorphological presentations and varied cytoplasmic pigmentation that can make difficult the histopathological diagnosis. The aim of this study was to evaluate the benefits of using Fontana Masson and bleaching in histopathology routine for the diagnosis of melanocytic neoplasms in dogs. Thirty-one samples diagnosed as melanocytic neoplasms were analyzed, among which, 21 are cutaneous neoplasms (13 melanomas and 8 melanocytomas); and 10 are oral melanomas. The samples with accentuated pigmentation were submitted to the bleaching technique (20), whereas the amelanotic samples were submitted to the Fontana Masson staining (11). In the bleached samples, a reassessment of nuclear pleomorphism and mitosis count was performed according to the guideline. In this study, two pigmented cutaneous neoplasms with obscured nuclei had their final diagnoses reconsidered after performing the bleaching technique. The Fontana Masson technique was performed on 11 amelanotic or slightly pigmented samples. Among them, six samples were oral melanomas, four cutaneous melanomas and one melanocytoma. In 10 samples it was possible to visualize argentaffin pigment evidenced by the technique. In an amelanotic skin sample, there was no marking using the Fontana Masson technique, which was referred for immunohistochemistry to confirm the diagnosis. Histochemical techniques employed in this study proved to be useful tools in the histopathological routine, with low cost, easy and quick execution. When used together with the recommendations of the guidelines for melanocytic neoplasms, they help both in differentiating the neoplasm and in determining the most accurate prognosis.