Haptotaxis of human breast cancer cells to extracellular matrix proteins. SUM 149 and SUM 102 cells (105) were placed into the top chamber of a Costar well coated with laminin (50 μg/ml) or collagen I (10 μg/ml) and allowed to invade for 24 hours. Invasive cells were stained with propidium iodide and quantified in 10 random microscopic fields. Micrographs were taken at 200× magnification. Data are expressed as mean ± SEM of at least three independent experiments.