Secretion of plasminogen activator by normal, reactive and neoplastic human tissues cultured in vitro

Plasminogen activator secretion by 39 primary or early‐passage cultures of malignant human neoplasms has been compared with that of 16 similar cultures of benign neoplasms and 39 cultures of normal or reactive tissue. While normal cells of mesenchymal or neural origin secreted considerably less plasminogen activator than did cells from frankly malignant tissues, elevated levels of enzyme secretion were also encountered in cultures of benign neoplastic or reactive cells. In the case of epithelial tissue, no consistent relationship between plasminogen activator secretion and neoplasia could be documented. Our failure to observe, for any particular cell type, a reproducible correlation between malignancy and plasminogen activator secretion may be attributable to the artificial conditions of in vitro culture, where normal in vivo regulatory mechanisms do not obtain.