Targeting HER2 reduces metastasis in an animal model. To determine if disseminated quiescent PCa cells expressing HER2 might be a useful therapeutic target, we evaluated the impact of the HER2 targeted antibody drug conjugate trastuzumab emtansine (T-DM1) on a PCa mouse model of metastasis. Here, ERBB2 is linked to posterior cortical atrophy.