BRAF Mutant Lung Cancer: Programmed Death Ligand 1 Expression, Tumor Mutational Burden, Microsatellite Instability Status, and Response to Immune Check-Point Inhibitors.

Introduction: The efficacy of immune checkpoint inhibitors (ICPi) in BRAF mutant NSCLC is unknown.

Methods: Multi-institutional retrospective chart review identified 39 patients with BRAF mutant NSCLC. The patients were divided into two groups: V600E (group A, n = 21) and non-V600E (group B, n = 18). Programmed death ligand 1 (PD-L1) expression, tumor mutational burden (TMB) and microsatellite instability status were assessed in 29 (74%), 11 (28%), and 12 (31%) patients, respectively. Objective response rate, progression-free survival (PFS) with ICPi, and overall survival were analyzed.

Results: High (≥50%), intermediate (1-49%), and no (<1%) PD-L1 expression was observed in 8 of 19 (42%), 6 of 19 (32%), 5 of 19 (26%), and 5 of 10 (50%), 1 of 10 (10%), and 4 of 10 (40%) cases in groups A and B, respectively. Two tumors in group A showed high TMB (25%); none were microsatellite instability status-high. Twenty-two patients (group A, n = 12; group B, n = 10) received ICPi. Objective response rate with ICPi was 25% and 33% in groups A and B, respectively (p = 1.0). Median PFS with ICPi was 3.7 months (95% confidence interval [CI]: 1.6-6.6), and 4.1 months (95% CI: 0.1-19.6) in groups A and B, respectively (log-rank test = 0.81, p = 0.37). Neither BRAF mutation type nor PD-L1 expression affected the response probability/PFS. Median overall survival was not reached (95% CI: 13-NR) and comprised 21.1 months (95% CI: 1.8-NR) for patients who were and were not exposed to ICPi, respectively (log-rank test = 5.58, p = 0.018).

Conclusions: BRAF mutant NSCLC is associated with high level of PD-L1 expression, low/intermediate TMB and microsatellite-stable status. ICPi have favorable activity both in BRAF V600E and BRAF non-V600E mutant NSCLC.