Atezolizumab plus anthracycline-based chemotherapy in metastatic triple-negative breast cancer: the randomized, double-blind phase 2b ALICE trial

Abstract

Immune checkpoint inhibitors have shown efficacy against metastatic triple-negative breast cancer (mTNBC) but only for PD-L1^positive disease. The randomized, placebo-controlled ALICE trial ( NCT03164993 , 24 May 2017) evaluated the addition of atezolizumab (anti-PD-L1) to immune-stimulating chemotherapy in mTNBC. Patients received pegylated liposomal doxorubicin (PLD) and low-dose cyclophosphamide in combination with atezolizumab (atezo-chemo; n = 40) or placebo (placebo-chemo; n = 28). Primary endpoints were descriptive assessment of progression-free survival in the per-protocol population (>3 atezolizumab and >2 PLD doses; n = 59) and safety in the full analysis set (FAS; all patients starting therapy; n = 68). Adverse events leading to drug discontinuation occurred in 18% of patients in the atezo-chemo arm (7/40) and in 7% of patients in the placebo-chemo arm (2/28). Improvement in progression-free survival was indicated in the atezo-chemo arm in the per-protocol population (median 4.3 months versus 3.5 months; hazard ratio (HR) = 0.57; 95% confidence interval (CI) 0.33-0.99; log-rank P = 0.047) and in the FAS (HR = 0.56; 95% CI 0.33-0.95; P = 0.033). A numerical advantage was observed for both the PD-L1^positive (n = 27; HR = 0.65; 95% CI 0.27-1.54) and PD-L1^negative subgroups (n = 31; HR = 0.57, 95% CI 0.27-1.21). The progression-free proportion after 15 months was 14.7% (5/34; 95% CI 6.4-30.1%) in the atezo-chemo arm versus 0% in the placebo-chemo arm. The addition of atezolizumab to PLD/cyclophosphamide was tolerable with an indication of clinical benefit, and the findings warrant further investigation of PD1/PD-L1 blockers in combination with immunomodulatory chemotherapy.

Fig. 1. Patient flow diagram.

The FAS included all patients who had received any IMP. The PP population comprised all patients who had received >3 doses of atezolizumab/placebo and >2 doses of PLD and could be evaluated for tumor response.

Fig. 2. Kaplan–Meier plots of survival outcomes and quality of life.

a–d, PFS assessed according to iRECIST in the PP population (a), the PD-L1^positive (b) and PD-L1^negative (c) PP population subsets and the FAS (d). e, OS in the FAS. f, Time to deterioration (reduction ≥20 points) of the global health status/quality of life score in the EORTC QLQ-C15-PAL questionnaire. The analysis includes the 62 patients (91%) in the FAS for whom a baseline value was available. The proportions of patients who completed this item at each of the subsequent timepoints are available in Extended Data Table 4. HRs with CIs were estimated using the Cox proportional hazards method. P values were calculated by the log-rank method.

Fig. 3. Subgroup analyses of PFS (FAS).

HRs (center square) with 95% CIs (error bars) for PFS in the atezo-chemo group versus the placebo-chemo group in the FAS. HRs with CIs were calculated using the Cox proportional hazards method. The number of patients in each subgroup/arm is indicated. Intrinsic subtype, PD-L1 status, TIS, tumor lymphocyte infiltration and TMB were not available for all patients.

Fig. 4. Effect of therapy on immune cell subsets and association of Tregs with PFS.

PBMCs collected at pre-trial screening and after 8 weeks of trial treatment were assessed for different immune cell subsets by flow cytometry. All patients in the FAS for whom paired samples were available were included in the analysis (placebo-chemo n = 18, atezo-chemo n = 29). The gating strategy is shown in Supplementary Fig. 1. Cell counts were estimated by multiplying the percentage of each subset within the lymphocyte gate by the clinical lymphocyte differential cell count obtained for each patient at each timepoint. Fold changes from screening were calculated and log₂-transformed. The baseline level is indicated with a dotted line. Data are presented as box and whisker plots, with the center line showing the median and the hinges showing the IQR. Whiskers show minimum and maximum values. a, Immune cell absolute cell counts. Immune cell subsets are defined as follows: CD4 T cells (CD3⁺CD4⁺CD8⁻), CD8 T cells (CD3⁺CD4⁻CD8⁺), Tregs (CD3⁺CD4⁺Foxp3⁺CD25^Hi), B cells (CD3⁻CD19⁺), NK cells (CD3⁻CD56⁺), NKT cells (CD3⁺CD56⁺) and gd-T cells (CD3⁺gd-TCR⁺). b, Percentage of T cell subsets. CD4 and CD8 subsets are shown as a percentage of total lymphocytes, and Tregs are shown as a percentage of total CD4⁺ T cells. Two-tailed P values were calculated using the Wilcoxon matched-pairs signed-rank test. c,d, Kaplan–Meier analysis of PFS in the placebo-chemo group compared to the atezo-chemo group in patients with low (≤ median; c) and high (> median; d) levels of Tregs as percentage of total CD4⁺ T cells. Two-tailed P values were calculated using the log-rank test and HRs with CIs using the Cox proportional hazards method.

Extended Data Fig. 1. Kaplan-Meier plots of progression-free and overall survival by PD-L1 status (FAS).

Progression-free survival by iRECIST in the PD-L1 positive (a) and negative (b) subgroups of the full analysis set. Overall survival in the PD-L1 positive (c) and negative (d) full analysis set. Hazard ratios with confidence intervals were calculated using the Cox proportional hazards method. PD-L1, Programmed death-ligand 1; FAS, full analysis set; HR, hazard ratio; CI, confidence interval.

Extended Data Fig. 2. Swimmer plot.

Duration of treatment and treatment responses in the PP population. The length of the bars represent the time from randomization to disease progression (iRECIST) or censoring. Symbols denote the first time a treatment response (other than progression) is documented, patients censored for progression, and the last date of study treatment.

Extended Data Fig. 3. Kaplan-Meier plots of progression-free survival with high and low Tumor Inflammation Signature.

Progression-free survival by iRECIST in the subpopulation with high (> 66^th percentile) and low (≤ 66^th percentile) tumor inflammation signature (TIS) in the atezo-chemo (a) and placebo-chemo (b) group. Tumor Inflammation Signature was assessed by analysis of pre-treatment biopsies on the NanoString BC360 assay. All patients in the full analysis set for whom samples were available were included in the analysis (placebo-chemo n = 17, atezo-chemo n = 27). Hazard ratios (HR) with confidence intervals (CI) were calculated using the Cox proportional hazards method.

Extended Data Fig. 4. Correlation between Tumor Inflammation Signature and other biomarkers.

a: Tumor Inflammation Signature (TIS) in patients with PD-L1 negative and positive tumors. Both analyses were done on archival pre-study biopsies. For 28 of the 44 patients, the analyses were done in the same tumor sample, while 16 of the tumors analyzed for PD-L1 did not contain enough material to be analyzed for TIS. For these biopsies, the Nanostring assay was performed on a different archival biopsy. b: TIS in patients with low and high infiltration of lymphocytes in tumor. Tumor-infiltrating lymphocyte (TIL) abundance was assessed in study-specific pre-treatment biopsies, whereas TIS was analyzed in archival biopsies, due to the limited volume of the screening biopsies. Tumor Inflammation Signature was assessed by a single analysis of pre-treatment biopsies on the NanoString BC360 assay. All patients for whom a suitable archival biopsy was available were included in the analysis (n = 44). PD-L1 expression (SP142 ASSAY) and TIL were assessed once for each biopsy, by two experienced breast cancer pathologists that were blinded for treatment arm and clinical outcome. Two-sided p-values were calculated using the Wilcoxon rank sum test. In the box plots, the center line represents the median value and the box limits represent the upper and lower quartiles. The whiskers extends to the extreme values, omitting outliers extending > 1.5 x IQR from the box limits, these are shown in the dot plot. TIS, Tumor Inflammation Signature; PD-L1, programmed death-ligand 1; TIL, tumor-infiltrating lymphocytes.