In patient-derived xenograft (PDX) tumors of breast adenocarcinoma, other investigators have described subpopulations of CAFs expressing the G protein-coupled C5a receptor 77 (GPR77, a.k.a. C5AR2) and membrane metallo-endopeptidase (MME, a.k.a. CD10) that promote tumor formation and chemoresistance by providing a survival niche for cancer stem cells. The gene discussed is C5AR2; the disease is neoplasm.