MET and neoplasm: To define a surface marker for tumorigenic stromal GCTB cells, we focused on c-Met, which has been identified as a strong CSC surface marker in other tumor entities, for example, pancreatic ductal adenocarcinoma.25 Immunohistochemistry of patient-derived GCTB tissue sections revealed that the cells are almost negative for c-Met, although some giant cells and some stromal cells exhibited a slightly enhanced red positive staining.