DPP4 and neoplasm: In melanoma, for example, fibroblasts expressing the cell surface marker CD26 are an important subpopulation of cells contributing to tumor stroma ECM deposition; in a mouse xenograft model of melanoma, depletion of the CD26-positive fibroblast subpopulation decreased tumor growth.10 In basal cell carcinoma, CAFs are known to express a variety of chemokines associated with both local immunosuppression and tumor progression.