Abstract
BACKGROUND
Non-small cell lung cancer (NSCLC) accounts for ~50% of brain metastases. We present the genomic and immune biomarker landscape for a cohort with metastatic NSCLC to the brain.
METHODS
We analyzed brain metastases FFPE tissue (n=137; ages 40-85y (mean 65y), 52% female, 48% male) vs. primary sites (n=5533; ages 24-100+y (mean 71y), 51% female, 49% male) for advanced or metastatic NSCLC patients with comprehensive genomic and immune biomarker profiling, including PD-L1 IHC, tumor mutational burden (TMB), Tumor Immunogenic Signature (TIGS), Cell Proliferation (CP), and Cancer Testis Antigen Burden (CTAB).
RESULTS
Genomic alteration (GA) frequency for NSCLC brain metastasis versus primary sites were similar among the most frequently mutated genes except for KRAS which was significantly higher among brain metastases (39.9% vs 25.5%, p< 0.0005). No significant differences were observed for TP53 (50.7% vs 50.2%), STK11 (11.5% vs 10.9%), CDKN2A (10.1% vs 7%), or EGFR (8.0% vs 11.5%). PD-L1 expression for all cases by IHC was not significantly different (mean TPS 29.9% vs 26.3%); however, brain metastases were more likely to be PD-L1 negative (TPS< 1%) (46.3% vs 33.3%, p< 0.005). Conversely, TMB was higher in brain metastases versus primary sites (12.9 vs 10.2 muts/MB, p< 8x10-10), with more TMB-high cases (10 muts/Mb) (57.0% vs 33.5%, p< 3x10-8). Similarly, brain metastases had a higher proportion of CTAB-high cases (68.6% vs 57.6%, p=0.01). The immune response biomarker score, TIGS, was more often weak in brain metastases (52.6% vs 34.0%, p< 9x10-6).
CONCLUSION
In NSCLC, metastatic brain lesions have a larger antigen burden, with increased TMB and CTAB, likely due to the immune privileged nature of the brain, which is reflected in the lower TIGS scores and PD-L1 positivity. Despite lower PD-L1 positivity, NSCLC brain metastases with negative PD-L1 IHC may potentially benefit from immunotherapy strategies given the high TMB and CTAB.