Circulating PRL and TSH (as a control) levels in EGFR or HER2 transgenic mice before and after treatment of oral lapatinib (100 mg daily for 3 wk). Same number (7 in each group) of mice were also treated with vehicle as a control. A, PRL levels before and after treatment in EGFR transgenic mice. B, PRL levels before and after treatment in HER2 transgenic mice. C, TSH levels pre- and postlapatinib in EGFR transgenic mice. D, TSH levels pre- and postlapatinib in EGFR transgenic mice *, P < .01; #, P > .05.