Joneja et al. used the first-generation gene sequencing method to compare MBC, triple-negative breast cancer, and HER2-positive and hormone-positive breast cancer, and found that the expression rate of PD-L1 in MBC was higher than that of the other three cancer subtypes (46% vs 9, 6, 6%, respectively; p < 0.001) (Joneja et al., 2017). Here, CD274 is linked to cancer.