CTSS and small cell lung carcinoma: Protease secretion of two CTC cell lines BHGc7 and BHGc10, derived from SCLC, is largely confined to MMP-9 and several members of the cathepsin family, with cathepsin S exclusively found in the CTCs and the metastatic and chemoresistant GLC16 cell line, but not in lines established from local metastases.