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

[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 nab-paclitaxel. 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.