CDKN1A and cancer: Several cell cycle inhibitors, including Cdkn1a, Cdkn2a, Mdm2, Trp53inp1, Ccng, and Notch1—a known tumor suppressor in head and neck squamous cell carcinoma (HNSCC)12—were upregulated in the control stem-like cell cluster but not in the cancer stem-like cell cluster (Fig. 5e; Supplementary Table 1).