Examples of HER-2 and p21WAF1/CIP1 immunoreactivity in infiltrating ductal carcinoma of the breast. Immunostaining was performed as described in Materials and methods, and nuclei were counterstained with haematoxylin. (a) A tumour showing HER-2 overexpression, with (b) a concomitant predominance of cytoplasmic p21WAF1/CIP1 staining and minimal or no nuclear p21WAF1/CIP1 expression. (c) A HER-2-negative tumour, with (d) a predominance of nuclear p21WAF1/CIP1 expression compared with cytoplasmic p21WAF1/CIP1 , which was proportionately less on intensity distribution scoring in 10 fields. Insets in panels (b) and (d) show higher-power views of the same fields. Magnification × 3–4.