Lapatinib and Trastuzumab With or Without Endocrine Therapy

The neoadjuvant setting is especially attractive for studies of predictive biologic correlates for several reasons including early assessment of response to therapy, access to the primary tumor, and reduced patient numbers compared to those required in the adjuvant setting. Response to neoadjuvant therapy is a validated surrogate marker for improved survival; it may be used to test the overall efficacy of neoadjuvant treatment regimens and response in the primary tumor mirrors the effect of therapy on micrometastases. 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. This is a phase II trial. Clinical efficacy will be assessed by bidimensional tumor measurements of the primary cancer at baseline, and at the end of week 12. Objective tumor response rate defined as objective bidimensional tumor measurements after neoadjuvant treatment at 12 weeks will be calculated, and assessed according to standard RECIST criteria. Pathologic responses will be graded as pathologic complete response if there is no invasive cancer in the residual breast at the time of surgery. Near pathologic complete response will also be documented as residual disease of less than 1 cm.