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The incidence of canine mammary tumours (CMTs) differs significantly between breeds, strongly supporting an influence of genetic risk factors. We aimed at identifying germline genetic variations in mammary tumour-associated genes in dogs and survey whether these might alter the encoded proteins. We sequenced 11 genes (BRCA1, BRCA2, BRIP1, CDH1, CHEK2, EGFR, ESR1, HER2, PTEN, STK11 and TP53) and screened for genetic variations. Sixty-four single nucleotide polymorphisms (SNPs) were identified. Nine of the coding SNPs were non-synonymous, of which four were located in gene regions conserved across four species. Three of the non-synonymous SNPs might be damaging according to PolyPhen predictions. One of the indels identified has previously been associated with CMTs. Because of the founder effects, genetic drift and inbreeding in many dog breeds the allele frequencies of the genes studied are likely to vary significantly between breeds and contribute to the considerable difference in genetic risk associated with cancer.

Canine mammary tumours (CMT) are the most common neoplasia in unspayed female dogs. CMTs are suitable naturally occurring models for human breast cancer and share many characteristics, indicating that the genetic causes could also be shared. We have performed a genome-wide association study (GWAS) in English Springer Spaniel dogs and identified a genome-wide significant locus on chromosome 11 (praw = 5.6x10-7, pperm = 0.019). The most associated haplotype spans a 446 kb region overlapping the CDK5RAP2 gene. The CDK5RAP2 protein has a function in cell cycle regulation and could potentially have an impact on response to chemotherapy treatment. Two additional loci, both on chromosome 27, were nominally associated (praw = 1.97x10-5 and praw = 8.30x10-6). The three loci explain 28.1±10.0% of the phenotypic variation seen in the cohort, whereas the top ten associated regions account for 38.2±10.8% of the risk. Furthermore, the ten GWAS loci and regions with reduced genetic variability are significantly enriched for snoRNAs and tumour-associated antigen genes, suggesting a role for these genes in CMT development. We have identified several candidate genes associated with canine mammary tumours, including CDK5RAP2. Our findings enable further comparative studies to investigate the genes and pathways in human breast cancer patients.

BackgroundThe limited within-breed genetic heterogeneity and an enrichment of disease-predisposing alleles have made the dog a very suitable model for the identification of genes associated with risk for specific diseases. Canine mammary cancer is an example of such a disease. However, the underlying inherited risk factors for canine mammary tumours (CMTs) are still largely unknown. In this study, 52 single nucleotide polymorphisms (SNPs) in ten human cancer-associated genes were genotyped in two different datasets in order to identify genes/alleles associated with the development of CMTs. The first dataset consisted of English Springer Spaniel (ESS) CMT cases and controls. ESS is a dog breed known to be at increased risk of developing CMTs. In the second dataset, dogs from breeds known to have a high frequency of CMTs were compared to dogs from breeds with a lower occurrence of these tumours.ResultsWe found significant associations to CMT for SNPs and haplotypes in the estrogen receptor 1 (ESR1) gene in the ESS material (best PBonf = 0.021). A large number of SNPs, among them several SNPs in ESR1, showed significantly different allele frequencies between the high and low risk breed groups (best PBonf = 8.8E-32, best PBPerm = 0.076).ConclusionsThe identification of CMT-associated SNPs in ESR1 in two independent datasets suggests that this gene might be involved in CMT development. These findings also support that CMT may serve as a good model for human breast cancer research.