Cyclin D1 immunohistochemical expression and somatic mutations in canine oral melanoma

Canine Oral Melanoma (COM) is the most frequent tumor with oral localization in dogs. Copy number gains and amplifications of CCND1, a gene coding for Cyclin D1, are the most frequent chromosomal aberration described in human non-UV induced melanomas. Twenty-eight cases of COM were retrieved from paraffin-blocks archives. Four-μm thick sections were immunostained with an antibody against human Cyclin D1 and Ki-67. Cyclin D1 and Ki-67 expressions were scored through two counting methods. DNA was extracted from 20 μm thick sections of formalin-fixed paraffin-embedded blocks. Pathological and surrounding healthy tissue were extracted independently. Cyclin D1 immunolabeling was detected in 69% (18/26) while Ki-67 was present in 88.5% (23/26) of cases. Statistical analysis revealed correlation between two counting methods for Cyclin D1 (r = 0.54 P = 0.004) and Ki-67 (r = 0.56 P = 0.003). The correlation found between Ki-67 and Cyclin D1 indexes in 16/26 cases labeled by both antibodies (r = 0.7947 P = 0.0002) suggests a possible use of Cyclin D1 index as prognostic marker. PCR analysis on CCND1 coding sequence revealed the presence of 9 somatic mutations in seven samples producing synonymous, missense and stop codons. Since none of the Single-Nucleotide Polymorphism (SNPs) were found to be recurrent, it is suggested that overexpression of Cyclin D1 may be the consequence of alterations of CCND1 upstream regions or other genetic aberrations not detectable with the methodology used in this study. Future studies are needed to verify the potential use of Cyclin D1 index as prognostic indicator and to highlight the molecular events responsible for Cyclin D1 overexpression in COMs. This article is protected by copyright. All rights reserved.