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. Here, CD6 is linked to cutaneous melanoma.