Mammosphere-derived cells from pleural effusions are tumorigenic. Five thousand uncultured or mammosphere-derived cells were injected into severe combined immunodeficiency disease mice, and tumour development was monitored. Survival graphs for PE14 (a) and PE66 (b) are shown. (c) Survival curves of mice injected with different numbers of cells (as indicated) derived from PE14 mammospheres. (d) Tumours derived from cells isolated from PE14 mammosphere cultures were removed, fixed, sectioned, and stained for CD24 (SWA11), MUC1, and CK14 and CK19 expression, as described in Materials and methods. CK, cytokeratin; H&E, haematoxylin and eosin; ms, mammosphere; PE, pleural effusion.