When TGFβ-stimulated breast cancer cell lines were cultured as a monolayer on either non-mineralized (Fig. 2A) or mineralized (Fig. 2B) bone matrix over a 24 h culture period there was significant degradation of the non-mineralized matrix (range 65–75%; Fig. 2A) and to a lesser extent the mineralized matrix (range 40–45%; Fig. 2B) only in the presence of plasminogen. This evidence concerns the gene PLG and breast cancer.