ABO blood type is associated with risk for several malignancies, but still is not clear if the risk of breast cancer is greater in carriers of certain ABO blood group. The aim of this study was to examine the correlation between ABO blood group genotypes and the occurrence of breast cancer, as well as the association between ABO blood group genotypes and the presence of certain tumor grades (I-III) and ER, PR, HER2 markers. The research included 59 patients who were diagnosed with invasive breast cancer and 80 asymptomatic, healthy women,voluntary blood donors. Genomic DNA was isolated from whole blood using commercially available reagent packages for isolation QIAampDNA Blood Mini Kit (QIAGEN, Germany). Genotyping of the five basic alleles (O1, O2, A1, A2, B) and 15 genotypes was performed using PCR-SSP method. By comparing genotypes and phenotypes of ABO blood groups between the patients and the control group, P>0,05 was obtained and there is no statistical significance for the correlation between ABO genotypes/phenotypes of the patient group and the control group. By examining the significance of different tumor grade occurrence, and ER, PR and HER2/neu status, it was discovered that there is no statistical significance for the appearance of a particular grade, and tumor markers ER status, PR and HER2 / neu status in O1A1 genotype compared to non-O1A1 genotypes of ABO blood group system. The thesis results confirmed that there is no correlation between ABO blood type genotypes/phenotypes and breast cancer in tested groups.