Safety and efficacy of tiragolumab, atezolizumab and chemotherapy for early-stage or PD-L1-positive advanced triple-negative breast cancer: a phase Ib study

Abstract

Background: Immune checkpoint inhibitors have transformed the management of triple-negative breast cancer (TNBC) but outcomes could be improved further. We explored combining the T-cell immunoreceptor with immunoglobulin and ITIM domains (TIGIT) inhibitor tiragolumab with atezolizumab-containing regimens for patients with early-stage or advanced TNBC. Patients and methods: This multinational open-label phase Ib study included two cohorts. In cohort A [programmed death-ligand 1 (PD-L1)-positive advanced TNBC], patients received first-line tiragolumab with atezolizumab and nabpaclitaxel. The primary endpoint was confirmed objective response rate. In cohort B (early-stage TNBC, irrespective of PD-L1 status), patients were randomised to receive tiragolumab, atezolizumab and sequential taxane- and anthracycline-based neoadjuvant therapy with (arm A) or without (arm B) carboplatin. The primary objective was to evaluate safety in arm A versus arm B. Results: Between September 2020 and October 2021, 83 patients were enrolled from 24 sites in eight countries. In cohort A (n = 41), the confirmed objective response rate was 54% [95% confidence interval (CI) 37% to 69%], median duration of response in 22 responding patients was 7.2 months (95% CI 4.9-13.1 months), median progression-free survival was 6.5 months (95% CI 5.4-9.0 months) and median overall survival was 24.6 months (95% CI 14.7 months-not estimable). Five patients (12%) discontinued tiragolumab for adverse events. In cohort B (n = 42), carboplatin was associated with more haematological effects but no increase in pathologic complete response rate [arm A: 46% (95% CI 24% to 68%); arm B: 55% (95% CI 32% to 77%)]. Adverse events led to treatment discontinuation in 23% and 20% of patients in arms A and B, respectively. Conclusions: The activity of tiragolumab-containing regimens appeared similar to that of atezolizumab plus chemotherapy in randomised phase III trials in early-stage and advanced TNBC. The safety profile of all three regimens was consistent with previous experience of similar regimens in other tumour types and with symptoms of the underlying disease. Clinical trial registration: ClinicalTrials.gov NCT04584112.