Pathologic and molecular responses to neoadjuvant trastuzumab and/or lapatinib from a phase II randomized trial in HER2-positive breast cancer (TRIO-US B07)

In this neoadjuvant trial (TRIO-US B07), participants with early-stage HER2-positive breast cancer (N=128) were randomized to receive trastuzumab (T), lapatinib (L), or both (TL) as HER2-targeted therapy, with each participant given one cycle of this designated anti-HER2 therapy alone followed by six cycles of standard combination chemotherapy with the same anti-HER2 therapy. We observed similar pathologic complete response (pCR) rates between T and TL, and a lower pCR rate with L. Higher-level amplification of HER2 and hormone receptor-negative status were associated with a higher pCR rate. Higher pre-treatment immune infiltrate trended toward higher pCR rate in T-treated groups, and greater HR expression correlated with lower immune infiltrate. Large shifts in tumor, immune, and stromal gene expression occurred after one cycle of HER2-targeted therapy. In contrast to pCR rates, the L-containing arms exhibited greater proliferation reduction than T at this timepoint. Immune expression signatures increased in all arms after one cycle of HER2-targeted therapy, decreasing again by the time of surgery. Our results inform approaches to early assessment of sensitivity to anti-HER2 therapy and shed light on the role of the immune microenvironment in response to HER2-targeted agents.