Patient population
The ATX study (BOOG-2006-06) was a multicenter, open-label, randomized phase II trial initiated in 2006. Women with confirmed HER2-negative locally recurrent or MBC were eligible. Patients were randomized between paclitaxel (day 1, 8, and 15) plus bevacizumab (days 1 and 15) (AT) at 4-week intervals for six cycles or paclitaxel (day 1 and 8) plus bevacizumab (day 1) plus capecitabine (ATX) at 3-week intervals for eight cycles. For this plasma analysis, we included samples from patients in the AT arm who received prior AI treatment in the adjuvant and/or metastatic setting. We only analyzed samples from the AT arm as the ATX trial showed a difference in progression-free survival (PFS) between the two treatment arms with a median PFS of 11.2 months in the ATX arm and 8.4 months in the AT arm [