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