Exosomal mRNA has emergedas a promising biomarker for molecularsubtyping of breast cancer, offering a noninvasive method. miRNAs such as miR-19a, miR-21, miR-24, miR-105,miR-155, miR-181b, and miR-210 have been recognized as promising biomarkersfor breast cancer diagnosis. The useof miR-375 and PD-L1 mRNA as endogenous biomarkers has demonstratedhigh accuracy and selectivity in diagnosing breast cancer. Another potential biomarker for breast canceris miR-660, which originates from breast cancer tumor–associatedmacrophages within the breast cancer microenvironment. The gene discussed is CD274; the disease is breast cancer.