Western blot analysis of Erb-B2 and EGF receptor expression in breast cancer cell lines, in CD34⁺ blood progenitor cells, and in primary tumor cells isolated from breast cancer patients. Total protein was extracted and 100 μg was run on a polyacrylamide gel unless otherwise indicated. After blotting, expression of Erb-B2 and EGF receptor was determined by staining with anti–Erb-B2 and anti–EGF receptor antisera as described in Materials and Methods.