Fig. 2. A subset of PRL-induced mammary cancers expresses the estrogen receptor α.

Immunohistochemistry of ERα in various mammary tumors (a-c) and the normal mammary epithelium (d); a, ERα-positive tumor, b, mixed lesion containing a subset of ERα-positive cells, c, ERα-negative cancer. Panel e shows a serial section of the mammary duct shown in panel d that was stained without the primary antibody against ERα. All slides were counterstained with hematoxylin (bar, 50 μm).