PLAUR and small cell lung carcinoma: The consistent presence of a small uPAR-positive subpopulation of cells in all primary (lung, Figure 1, lower panels A, B, C) and metastatic (bone marrow; Figure 1, lower panels D, E, and brain; F) SCLC cell lines, in contrast to other markers, which varied in abundance, suggests that uPAR-positive cells may comprise a functionally unique subpopulation of cells.