Breast Cancer · Medical · Advanced / Metastatic

IMpassion131

In first-line advanced TNBC, does atezolizumab plus conventional paclitaxel improve outcomes versus paclitaxel alone?

Trial design and population

Population / eligibility

651 patients with previously untreated unresectable locally advanced or metastatic TNBC; 45% had PD-L1-positive tumours by SP142 immune-cell assay.

Intervention vs comparator

Atezolizumab 840 mg IV days 1 and 15 plus paclitaxel 90 mg/m² days 1, 8 and 15 every 28 days vs placebo plus paclitaxel.

Sample size

651

Primary endpoint

PFS in PD-L1-positive population

Key results

In PD-L1-positive disease, median PFS was 6.0 vs 5.7 months (HR 0.82, 95% CI 0.60–1.12; P=.20). Final median OS was 22.1 vs 28.3 months (HR 1.11, 95% CI 0.76–1.64), showing no benefit.

Source-reported outcome visualization

Median PFS (PD-L1-positive) · Median

Atezolizumab + paclitaxel

6 months

Placebo + paclitaxel

5.7 months

Bars are scaled to the larger reported group value; endpoint, unit and horizon are labelled. Values are source-reported, not estimated from medians.

Absolute Effect

No statistically significant PFS benefit or OS benefit was demonstrated. Numerical OS difference is not proof of harm because the CI includes benefit and harm.

NNT: Not applicable; benefit was not demonstrated. Use only at the stated endpoint/time horizon; median survival differences are not converted into NNT.

NNH: Not quantifiable. Paclitaxel-related neuropathy and myelosuppression remain important; immune-mediated events are possible. NNH is not quantified because no single fixed-time excess-harm endpoint is selected.

Time-to-event hazard ratios and median survival are not treated as absolute risk differences. Where no defensible fixed-time NNT/NNH is available, the source-reported endpoint is visualized instead.

Safety and treatment burden

Paclitaxel-related neuropathy and myelosuppression remain important; immune-mediated events are possible. NNH is not quantified because no single fixed-time excess-harm endpoint is selected.

Follow-up, maturity and limitations

Follow-up: Final OS analysis reported 2021.

Do not generalize IMpassion130's findings to conventional paclitaxel in IMpassion131. Different chemotherapy backbone and trial outcomes matter.

Clinical interpretation

IMpassion131 failed to show benefit from adding atezolizumab to conventional paclitaxel; it should not be treated as equivalent to IMpassion130 or KEYNOTE-355.

Current-practice context · reviewed 20 October 2026

This page separates the original trial findings from contemporary treatment sequencing. Confirm current guidelines, local regulatory status, biomarker requirements, prior treatment exposure and patient-specific contraindications before applying the evidence. Historical comparators may no longer represent the current standard; subgroup findings and immature endpoints are labelled rather than generalized.

Primary and authoritative sources

Miles D, et al. Primary results from IMpassion131. Ann Oncol. 2021. Source ↗

ClinicalTrials.gov NCT03125902 Source ↗