CD109 and melanoma: CD109, a GPI-linked cell membrane protein [26], has been reported to be highly expressed in many types of tumors, such as lung, oral and cutaneous squamous cell carcinomas (SCC), urothelial carcinomas, malignant melanomas, triple-negative breast cancer (TNBC), esophageal squamous cell carcinoma and gallbladder cancer [27–34], but not in most normal human tissues, except for myoepithelial cells of mammary, lacrimal and salivary glands and basal cells of prostate and bronchial epithelia [35].