Detection of single nucleotide polymorphisms (SNPs) in HER2, MUC1, ESR1, and BRCA1 genes associated with canine mammary cancer,Detekcija polimorfizama jednog nukleotida (SNP-a) u HER2, MUC1, ESR1 i BRCA1 gena povezanih s tumorom mliječne žlijezde kuja