Markers of proliferation (Ki67) and downstream kinase signaling (pMAPK) in A431 epidermoid carcinoma xenografts were decreased after treatment with panitumumab. Fixed tissue sections were prepared from A431 xenograft tumors from mice treated with either 500 μg IgG2 control vehicle or 500 μg panitumumab twice a week for two weeks. Qualitative changes in Ki67 or pMAPK immunoreactivity were visualized with DAB and hematoxylin counterstain. Micron bars = 100 μm for low magnification images on the left and 10 μm for high magnification images on the right. Representative fields are shown.