Invasion and anchorage-independent growth of breast cancer cells in the presence of premenopausal African-American or Caucasian-American breast extracellular matrix molecules (ECM). (a) Cell invasion through transwell inserts, precoated with equal amounts of ECM. Data are representative of four independent experiments. (b) Soft agar assays. Cells were stained with nitrobluetetrazolium before counting after 10 days of growth. The entire dish was analyzed and colonies larger than 1 μm in diameter were counted. Data represent mean ± standard error of three separate experiments. *P < 0.05 **P < 0.01, ***P < 0.001; paired t test. (c) Gelatin zymography. ECM was isolated from six pools of 3-7 patients/pool. Results are representative of three experiments performed in triplicate. AA = African-American; CAU = Caucasian-American.