MDA/RLN2 xenografts show immunohistological features of differentiation. Tissue sections from MDA/EGFP (left column) and MDA/RLN2 tumours (right column) were stained with (a, b) haematoxylin and eosin and (c, d) picrosirious red showing smaller groups of tumour cells surrounded by collagen fibres in MDA/RLN2 tumours. Representative sections of the immunodetection of smooth-muscle actin are shown in (e) and (f). The primary antibody was substituted with an isotype control immunoglobulin and a representative control section is shown (insert in f). MDA/RLN2 tumours contained more smooth muscle actin positive cells then MDA/EGFP tumours. (g) A section of human mammary gland tissue was used as positive control and showed smooth muscle actin staining in the myoepithelial cells surrounding the alveoli. (h) Staining for the proliferation marker Ki67 revealed numerous positive nuclei in proliferative regions in the periphery of MDA/EGFP and MDA/RLN2 tumours, an example is shown here for MDA/RLN2. Magnification: ×400.