Clinical, molecular, and immunologic profiling of brain metastases (BM) in head and neck squamous cell carcinoma (HNSCC).

6036 Background: BM is a rare complication of HNSCC that carries a high rate of morbidity and poor prognosis. Clinical risk factors, molecular characteristics, and the immunogenicity of HNSCC BM are not well defined, leaving a critical knowledge gap in this field. We performed one of the largest multi-institutional analyses summarizing the clinical, molecular, and immunologic profile of 61 cases of BM-HNSCC. Methods: We conducted a pooled analysis of the clinical characteristics pertaining to BM-HNSCC from 3 academic institutions (n=24). Next-generation sequencing (NGS) and immune profiling (IP) of primary and BM specimens was conducted on a subset of cases (n=19 and n=16, respectively); there were 3 paired samples for NGS and 0 for IP. Four samples (2 BM and 2 non-BM) were submitted to Phase Genomics, Inc for evaluation of structural variants in BM genomes by proximity ligation sequencing (PLS). These results were complimented by a comparative analysis of genomic alterations in an additional cohort of BM (n=37) and local samples (n=4082) submitted for NGS at Foundation Medicine, Inc (FMI). Statistical comparisons were done using Fisher’s exact testing of 2x2 contingency tables with p-values controlled for FDR by the Benjamini-Hochberg procedure. Results: Clinical features were as follows: median age at diagnosis 59 years, 75% male, 55% current/former smokers, 75% oropharyngeal primary, and 84% HPV+ or p16+. The most frequently altered genes in BM specimens (62% HPV/p16+) were ATM (54%), KMT2A (54%), PTEN (46%), RB1 (46%), and TP53 (46%). BM and non-BM samples demonstrated significant levels of structural rearrangement ranging from 9 to 90 variants by PLS. IP identified lower densities of CD8+, PD1+, PDL1+, and FOXP3+ cells in BMs compared to primary tumors. PDL1 combined positive scores were <1% in 12/13 unpaired samples (92%; 10 BM and 2 primary). The FMI BM-HNSCC cohort (51% HPV+) identified CDKN2A (40.5%), TP53 (37.8%), and PIK3CA (27.0%) as the most frequently altered genes. Enrichment analysis of the FMI cohort showed MAP2K2 alterations significantly enriched in BM (11.8% vs 6.4%, P=0.005) and TSC1 alterations significantly enriched in the local site (67.3% vs 37.8%, P=0.008). HPV+ was also significantly enriched in the BM cohort (51.25% vs 26.11%, P=0.001). Overall survival from BM diagnosis was 6m (range 0-27m). Conclusions: HNSCC patients with BM have higher-than-expected proportions of oropharyngeal primary site and HPV/p16-positivity. The most frequent molecular alterations in BM samples are also commonly found in non-BM HNSCC, including targetable PIK3CA alterations. MAP2K2 alterations were significantly enriched in BM compared to non-BM samples, which warrants further investigation. BM samples also tended to have lower markers of immunogenicity. This latter finding could have important clinical implications when considering immunotherapy or immune-modulating drugs.