Trastuzumab is an efficacious agent in HER2 overexpressing breast cancers. Our results with neoadjuvant trastuzumab indicate that its efficacy may be better in patients with treatment-naïve tumors compared to metastatic disease, with 26% of patients showing a partial response after only 3 weeks of therapy. No patients progressed during this 3-week period. We have also conducted a neoadjuvant lapatinib study given as a single agent for 6 weeks. The response rates in this second study have been impressive with greater than 80% responses in patients with HER2 positive locally advanced breast cancers. It is likely that the true response rate to HER2 blockade would be higher had therapy been continued for longer. We therefore hypothesize that lapatinib, a dual tyrosine kinase inhibitor, together with trastuzumab, will result in tumor regression when given as neoadjuvant therapy in HER2 overexpressing breast cancer. We will compare lapatinib plus trastuzumab for 12 weeks, and if the tumors express ER, estrogen deprivation will also be administered.