TPS1104Background: Treatment for mTNBC is limited, with chemotherapy the mainstay (bevacizumab is approved in > 80 countries). Atezolizumab (atezo; MPDL3280A), a humanized anti-PDL1 antibody, inhibits PD-L1 binding to PD-1 and B7.1 but leaves PD-L2/PD-1 binding intact. mTNBC has high levels of tumor-infiltrating immune cells, increased PD-L1 expression and high mutation rates that may generate immunogenic neoantigens, making it a good candidate for PD-L1–targeted therapy. It is hypothesized that atezo’s single-agent activity in TNBC could be enhanced with chemotherapy by exposing the immune system to high levels of tumor antigens and modulating T-cell and NK cell functions. Nab-paclitaxel (pac) has high antitumor activity that may favorably alter the immune microenvironment, and atezo + nab-pac resulted in promising activity and tolerable safety. A Phase III multicenter, randomized, double-blind, placebo-controlled trial (IMpassion130) has been initiated to evaluate atezo + nab-pac in first-line mTNBC. Me...