Phase I/II Study of Lapatinib in Combination With Paclitaxel as 1L Chemotherapy for ErbB2-positive MBC

These subjects will receive weekly paclitaxel (80 mg/m2 IV for 3 weeks in a 4 week cycle) plus lapatinib (1500 mg once daily, starting on the second day of phase I). Subjects will receive a daily dose of lapatinib until disease progression or withdrawal from study treatment due to unacceptable toxicity or withdrawal of consent. Study completion is defined as deaths after administering study treatment for more than once. Subjects will be treated with paclitaxel for standard of 6 cycles, and may be continued at the discretion of investigators. If the subject experiences progression, an unacceptable toxicity related to paclitaxel, or termination of lapatinib therapy, paclitaxel therapy must be terminated any time of study period, even before 6 cycles of paclitaxel are given.