Immunostaining of MMP expression on paraffin embedded breast cancer tissue sections. MMP-1, -2, -3, -10, -11, -13, -14, -15 and -19 expression (brown colour) in normal breast tissue and breast cancer tissue grade 3 (G3) was visualized using specific antibodies (listed in Table 3). Staining was predominantly restricted to the cytoplasm and nuclei of tumor cells, whereas staining of stromal cells was rare, e.g. immunostaining of MMP-1, -2 and -10 shows a clear preference for the tumor cell nuclei with slight to moderate additional staining of the cytoplasm of tumor cells (A, C, G). MMP-13 showed a weak to moderate staining of the tumor cells cytoplasm as well as a staining of the cytoplasm of normal breast cells (K and L). MMP-15 showed a strong staining in the cytoplasm and in some nuclei of tumor cells and additional slight staining of stromal cells (O). MMP-11 and -19 staining was strong in the cytoplasm of tumor cells with additional slight staining of stromal cells and some nuclei of tumor cells (I and Q). MMP-3 and -14 showed a clear predominant staining of the tumor cells cytoplasm (E and M). Immunostaining of normal breast tissue served as control. Except MMP-13 (L), low to no staining for the abovementioned MMPs was found in normal breast tissue. Tissue stained with an irregular antibody served as negative control (S and T). Magnification: ×250 for all pictures, ×400 for detail included into the upper right corner adjacent to the corresponding tumor tissue picture; ×400 for HE-staining included into the bottom right corner adjacent to the corresponding tumor tissue picture; brown: DAB, blue: hematoxylin counter stain, purple: hematoxylin-eosin counter stain.