ADAM33 and breast cancer: The human breast cancer cell lines PMC42, MCF7 and SKBR3, which are positive for ADAM33 expression (Fig. 1A), showed a positive cytoplasmic staining (Fig. 1C,D and E) similar to what was previously observed in lung tissues in which only 10% of the ADAM33 produced is directed to the extracellular membrane in airway epithelium16.