A Phase II, Randomized, Open-label Study of Lapatinib Plus Chemotherapy Versus Trastuzumab Plus Chemotherapy in HER2-positive and p95HER2-positive Metastatic Breast Cancer

This is a Phase II, randomized, open-label, multi-center study evaluating the efficacy and
safety of lapatinib in combination with chemotherapy versus trastuzumab in combination with
chemotherapy in women with HER2-positive and p95HER2-positive metastatic breast cancer
(MBC). Eligible subjects will have newly diagnosed metastatic breast cancer (Stage IV)
either as a primary diagnosis or as a recurrence following treatment of curative intent; not
have received systemic or local treatment for MBC and have breast cancer that is positive
for HER2 and p95HER2. The primary objective is to compare progression-free survival (PFS)
of lapatinib plus chemotherapy versus trastuzumab plus chemotherapy as first-line treatment
in subjects with MBC exhibiting concurrent HER2 overexpression (and/or gene amplification)
and expression of carboxy-terminal fragments of HER2 (p95HER2). The secondary objectives are
to evaluate overall survival, overall response rate, clinical benefit response rate and the
safety as well as tolerability of lapatinib plus chemotherapy and trastuzumab plus
chemotherapy.