The immune escape ability of the ER+ breast cancer cell population was evaluated by using the TIDE database (http://tide.dfci.harvard.edu/) (Figure 6A), and there were significant differences in the immune response ability in the groups with high and low infiltration of the C4 subpopulation, the results of which indicated that a higher percentage of C4 subpopulation exhibited a lower immune response (Figure 6B). Here, C4A is linked to breast cancer.