Further phenotypic characterization indicated that, compared to healthy individuals, in BC patients, not only the total fraction of circulating MDSCs (HLA-DR- CD33+ cells) is increased, but the fractions of each of the MDSC subpopulations, including G-MDSCs (HLA-DR- CD33+ CD15+) and in particular M-MDSCs (HLA-DR- CD33+ CD14+), are also elevated. This evidence concerns the gene CD33 and breast cancer.