To reduce dimensionality and visualize trends in the data, we stratified tumor composition into 3 cohorts (>1%, 0.01–0.99%, <0.01%) and performed principal component analysis (PCA) on the 9 variables that we had measured (CK8, CK14, Zeb1, EpCAM, MHC-I, PD-L1, proliferation rate, in vitro fold change in contribution to the BC Pool, and in vivo fold change in contribution during tumor progression) (Supplementary Table 9). Here, CD274 is linked to breast cancer.