Immunohistochemical analysis of cyclin D1 expression in canine oral melanoma: A preliminary study

Introduction: Cyclin-D1, a positive regulator of the G1–S transition during the cell cycle, has been found to be overexpressed in a high percentage of human non UV-induced melanomas. The aim of this study was to investigate cyclin-D1 expression in canine oral melanomas (COMs). Materials and Methods: Twenty-one formalin-fixed, paraffin wax-embedded, Ki67+ histological sections of COMs from the archive of the University of Padova were immunohistochemically labelled with monoclonal antibodies specific for cyclin-D1 (VENTANA®). Weak positivity or positivity in <10% of neoplastic cells was considered as negative. Positivity for cyclin-D1 and Ki67 was expressed as an index (I) and calculated as the average number of positive cells in five high-power fields. Results: Seven out of 21 samples (33.3%) showed strong nuclear positivity for cyclin-D1 distributed diffusely or in clusters within the tumour. Cyclin-D1I was lower than the Ki67I in 5/7 cases. In the remaining two cases, due to the presence of cytoplasmic non-specific labelling, Ki67 positivity was not consistently assessed. Conclusions: This study demonstrates the immunohistochemical expression of cyclin-D1 in COMs. Cyclin-D1I is easier than Ki67I to obtain because of the lower number of positive cells. Furthermore, cyclin-D1 antigen seems to be more preserved in archive material. However, the characteristics of cyclin-D1 expression need to be confirmed with a higher number of cases and, for the possible restricted pattern of positivity, only complete excision should be taken in consideration for further studies. These data encourage future studies on the role of cyclin-D1 in COM pathogenesis and its possible prognostic significance.