Phase II multicohort study of atezolizumab monotherapy in multiple advanced solid cancers

The programmed death-ligand 1 inhibitor atezolizumab had shown clinical activity against several advanced malignancies.

This phase II, open-label basket study (NCT02458638) was conducted in 16 main cohorts of patients aged ≥18 years with stage III or IV solid tumors. In stage I, 12 patients were enrolled into each cohort. Treatment was atezolizumab 1200 mg intravenously every 3 weeks until loss of clinical benefit or unacceptable toxicity. The primary efficacy endpoint was the non-progression rate (NPR) at 18 weeks in treated, assessable patients. NPR ≤20% was not of interest for development as monotherapy, and NPR ≥40% was defined as the threshold of benefit/success. If ≥3 patients had non-progressive disease in stage I (interim analysis), 13 additional patients could be enrolled into stage II (final analysis). Secondary efficacy and safety endpoints were also evaluated.

Overall, 474 patients were enrolled and treated; 433 were included in the efficacy set. Due partly to slow recruitment because of competing trials and limited efficacy at interim analyses, enrollment was stopped early, including in cohorts that passed stage I boundaries of success. NPR was >20% in five cohorts: cervical cancer {n = 27; NPR 44.4% [95% confidence interval (CI) 25.5% to 64.7%]}; follicular/papillary thyroid cancer [n = 11; 54.5% (95% CI 23.4% to 83.3%)]; thymoma [n = 13; 76.9% (95% CI: 46.2% to 95.0%)]; gastroenteropancreatic (GEP) and lung neuroendocrine tumors [NETs; n = 24; 41.7% (95% CI 22.1% to 63.4%)], and low/intermediate grade carcinoid GEP and lung NETs [n = 12; 58.3% (95% CI 27.7% to 84.8%)]. Treatment-related adverse events occurred in 55.3% of patients overall, and at grade 3, 4, and 5 in 10.3%, 1.7%, and 0.4%, respectively.

Atezolizumab monotherapy was effective in the cervical cancer cohort. The interim benefit threshold was crossed in patients with follicular/papillary thyroid cancer, thymoma, and GEP and lung NETs, but recruitment was stopped before these signals could be confirmed in stage II. Safety was consistent with previous findings.