Serum miR-373 was significantly upregulated in the human epidermal growth factor 2–negative (p < 0.001), estrogen receptor–positive (p < 0.005), and progesterone receptor (PR)-positive (p < 0.024) in BC patients, and serum miR-155 was significantly upregulated in PR-negative (p < 0.001) BC patients while both serum miR-155 and miR-373 were positively correlated with the tumor grade. This evidence concerns the gene ESR1 and neoplasm.