PCNA and cancer: Based on the expression of cell cycle‐related genes (MKI67 and PCNA) and the cell cycle scores (Figure 1H; Figure S3B, Supporting Information), the following two types of proliferating cancer cells were identified: a fast‐proliferating cancer cell subpopulations (FPCS) associated with each donor‐specific cluster (Figure 1G) and a unique cancer cell cluster predominantly comprising proliferating cells (Figure 1G).