The tumor microenvironment (TME) and atezolizumab + nab-paclitaxel (A+nP) activity in metastatic triple-negative breast cancer (mTNBC): IMpassion130.

1006 Background: IMpassion130 was the first randomized phase 3 study to show clinical benefit of cancer immunotherapy (CIT) in untreated PD-L1+ mTNBC. Enhanced A + nP efficacy vs placebo (P) + nP was seen in pts with a richer immune TME but was confined to PD-L1 IC+ pts (PD-L1–expressing immune cells on ≥1% of tumor area; Emens JNCI 2021). While TNBC molecular subtyping and CD8 localization are prognostic in early TNBC, it is unknown whether these features are associated with CIT benefit in mTNBC. This exploratory analysis aimed to identify TME components associated with A + nP efficacy in IMpassion130. Methods: IHC was used to assess PD-L1 status (VENTANA SP142) and immune phenotypes (inflamed/excluded/desert per CD8 stromal/intratumoral localization; Mariathasan Nature 2018). RNA-seq was used for molecular subtyping (Burstein CCR 2015) and pathway analyses (MSigDB Hallmark). Cox regression was used to compare PFS/OS between A + nP vs P + nP, adjusted for prior taxanes, liver mets. Results: Sample classification and PD-L1 distribution are shown (Table). Improved PFS with A + nP vs P + nP was seen in PD-L1 IC+ inflamed and excluded tumors, but improved OS was limited to PD-L1 IC+ inflamed tumors. PD-L1 IC+ basal-like immune activated (BLIA) and immune suppressed (BLIS) subgroups derived PFS benefit, but OS benefit was limited to PD-L1 IC+ BLIA subgroups. In PD-L1 IC+ pts, pathway analysis identified proliferation/DNA damage repair (basal-like tumor features) and angiogenesis/ER response (higher in luminal androgen receptor [LAR]/ mesenchymal [MES] tumors) were associated with improved and reduced PFS, respectively. Conclusions: PD-L1 IC+ immune-inflamed tumors and PD-L1 IC+ BLIA tumors show highest CIT sensitivity, and LAR tumors may be resistant to CIT. These data warrant further study and validation. Clinical trial information: NCT02425891 .[Table: see text]