Histopathological features of tumor xenografts from MDA-MB-231 cells transfected with control vector, Sulfatase 1 or Sulfatase 2. A-C) Masson's trichrome staining of tumor xenografts. D) CD31 (PECAM) staining of tumor xenografts. The scale bar represents 400 μm for row A, 100 μm for row B, and 50 μm for rows C and D. Control group tumors exhibited higher cellular density and prominent mitotic activity (white arrow in row C), whereas the Sulfatase 1 and Sulfatase 2 group tumors contained more connective tissue and collagen (black arrows in rows B and C). For the tumors present, vessel density quantification of CD31 (PECAM) staining showed no significant differences between groups. Analogous data for the transfected tumors co-expressing Sulfatase 1 and 2 are not available due to tumor regression.