Boxplot analysis of densitometrically quantified expression of MMP protein. Protein levels were normalized to the corresponding expression of β-actin. For each MMP six boxes are mapped. The first three boxes are representing the expression of the inactive MMP form (white box: expression in normal breast tissue, light grey box: expression in grade 2 (G2) and dark grey box: expression in grade 3 (G3) breast cancer tissue). The remaining three boxes represent the expression of the active MMPs. The line within the boxplot corresponds to the median value, the box length to the interquartile range, and bars indicate the smallest and largest observations.