Evidence for the induction of a tumour associated cell surface protease on cytologically normal epithelial cells present in the sputum of patients possessing lung tumours.

Sputum obtained from healthy subjects and patients with known lung tumours has been challenged with fluorescent probes for the presence of an active cell surface protease. The mature epithelial cells from healthy patients' sputum lacked ability to bind these fluorescent probes whilst the majority of mature epithelial cells in the tumour patients' sputum bound these probes and consequently fluoresced. This demonstrable difference in the cell surface chemistry of mature epithelial cells was linked to the presence of lung tumour cells, which also possessed this cell surface protease. The mechanism of this induced cell surface enzyme appearance is not understood.