A subpopulation of grade IV human GBM display follistatin expression. Figure 6. Follistatin expression by subsets of tumor cells within the glioblastoma multiforme (GBM) tumor cell bulk. Samples from GBM patients were freeze sectioned and subsequently stained using a follistatin antibody against the human antigen. A) Central tumor sections of patient A. A few selectively follistatin positive cells are seen within the central portions of the tumor. B) Central section from patient B. Follistatin expression is seen in a subset of tumor cells within the central bulk of the tumor. The histological examination of patient A and B tumors displays a heterogeneity within the tumor bulk with both positive and negative tumor cells. As negative control, the primary antibody was omitted, C. Scale bars indicate 50 μm.