For example, CD6, a crucial gene for T-cell activation, is identified as a favourable prognostic marker in multiple cancers, such as breast invasive carcinoma (BRCA), cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC), head and neck squamous cell carcinoma (HNSC), and skin cutaneous melanoma (SKCM), as shown in Fig. 3b. The gene discussed is CD6; the disease is head and neck squamous cell carcinoma.