CHICAGO – according to interim findings from the ongoing and a retrospective analysis of data from several prior studies.
The retrospective analysis also demonstrated the value of tissue tumor mutational burden (tTMB) as a biomarker for checkpoint inhibition benefit in patients with metastatic urothelial carcinoma and melanoma.
Progression-free survival (PFS) at a minimum of 6 months in 58 evaluable NSCLC patients from the single-arm phase 2b B-F1RST study of first-line atezolizumab monotherapy was 9.5 vs. 2.8 months in those with a high (16 or greater mutations/coding sequence) vs. low (less than 16 mutations/coding sequence) blood tumor mutational burden (bTMB) score (hazard ratio, 0.49),, reported during an oral abstract session at the of the American Society of Clinical Oncology.
Progression-free survival hazard ratios improved as bTMB scores increased, explained Dr. Velcheti, associate director of the Center for Immuno-Oncology Research at Taussig Cancer Institute, Cleveland Clinic.
“At the prespecified cutoff of 16, the hazard ratio is 0.51 and this suggests strong correlation of bTMB with clinical benefit,” he said.
The objective response rate in these biomarker evaluable patients was 12.1% and the disease control rate was 25.9%; in the high vs. low bTMB patients the overall response rate was 36.4% vs. 6.4%, he noted, adding that the responses in the high bTMB patients were deeper and more durable, and the safety profile of atezolizumab () in the trial thus far is consistent with the known adverse event profile for the agent.
Further, prior studies, including the randomized phase 3
In the current study, bTMB was evaluated prospectively for the first time as a predictive marker for first-line atezolizumab in stage IIIb-IVb locally advanced or metastatic NSCLC using a next-generation sequencing-based panel. Patients were treated with atezolizumab at a dose of 1,200 mg intravenously every 3 weeks until disease progression, unacceptable toxicity, or loss of clinical benefit.
The findings show preliminary utility of bTMB as a predictive biomarker for PFS and ORR, and further support bTMB selection of patients in the ongoing phase 3 B-FASTtudy, which is currently enrolling, Dr. Velcheti said, noting that the findings are encouraging, as 30% of patients with NSCLC have inadequate tumor tissue for molecular testing at diagnosis.
B-F1RST is also ongoing, but has completed enrollment at 153 patients. Primary analysis results will be presented later this year, he said.
Similarly, tTMB was associated with checkpoint inhibitor efficacy across tumor types and lines of therapy in the retrospective analysis of data from seven atezolizumab monotherapy trials.
The overall response rate (ORR) in 987 patients from those studies was 16%, but the response rates were 30% vs. 14% in 125 patients with high tTMB scores vs. 812 patients with low tTMB scores,, reported during the oral abstract session.
Median duration of response (DOR) was 16.6 months overall but was 29 vs. 14 months in those with high vs. low tTMB scores, respectively, added Dr. Gandara, a professor and director of the thoracic oncology program at the University of California, Davis.
This association was not seen in control cohorts of the three randomized studies included in the analysis (OAK, POPLAR, and), he noted, explaining that the pooled overall response rate in controls was 14.9%, and the response rate in those with high vs. low tTMB scores was 14.4% and 15.1%, respectively.
Further, an exploratory analysis of the three randomized studies showed that PFS increased with increasing levels of tumor mutational burden (TMB). The hazard ratio for PFS at TMB greater than or equal to 16 was 0.71, and the association occurred only in patients receiving atezolizumab.
“As has been previously reported from other studies, [high TMB] identifies a patient population which is distinct from [programmed death-ligand 1] immunohistochemistry and yet complementary,” he said, noting that both high tTMB and high PD-L1 have been shown to predict response independently, and in the current study it is the “small proportion of patients with both [high] TMB and PD-L1 ... that have the best response rate.”
The findings, which highlight “the association of high TMB and enrichment of ORR, DOR, and PFS benefit with atezolizumab monotherapy across indications and lines of therapy,” and demonstrate that high TMB may serve as a surrogate for neoantigen load (NAL – a component of TMB that has been linked with immune response) and complement PD-L1 expression in enriching for clinical benefit from immunotherapy, he concluded, noting that harmonization efforts are underway to standardize TMB platforms and computational algorithms.
Dr. Velcheti has reported financial relationships with Amgen, AstraZeneca/MedImmune, Bristol-Myers Squibb, and many others. He has received research funding to his institution from Alkermes, Altor BioScience, Atreca, Bristol-Myers Squibb, and others. Dr. Gandara reported financial relationships with ARIAD, AstraZeneca, Boehringer Ingelheim, Celgene, and many others. He has received research funding to his institution from AstraZeneca/MedImmune, Bristol-Myers Squibb, Clovis Oncology, Genentech, and others.
SOURCES: Velcheti V et al. ASCO 2018 ; Legrand FA et al. ASCO 2018 .