Patients ( pts ) with hormone receptor positive MBC , irrespective of HER-2 status , were randomly assigned to T T + L group , tamoxifen in cycle 1 for 28 days then adding lapatinib on day 1 of cycle 2 ; or L T + L group , lapatinib in cycle 1 for 14 days , then adding tamoxifen on day 1 of cycle 2 to evaluate the potential drug-drug PK interaction at steady-state .