Levels of PRL, p-Akt, p-Erk and t-Erk expression were analyzed by immunoblotting using pituitaries derived from EGFR (A) or HER2 (B) transgenic mice treated with oral lapatinib or vehicle (100 mg daily for 3 wk). Four mice were selected based on matched tumor size (>3 × 2 mm), and effectiveness of lapatinib or vehicle on PRL level in each individual mouse is depicted above the blot. C, Histochemical staining of PRL, p-Erk, and p-Akt in pituitary glands derived from EGFR transgenic mice treated with lapatinib or vehicle were analyzed (×20 magnification).