Survival of gastric cancer (GC) patients is not determined by the predominant genomic ancestry (PGA): Results from an ethnically admixed Brazilian cohort of GC patients.

Abstract

e15588 Background: Clinical characteristics, treatment response and overall survival of GC patients differ between Asian and non-Asian countries. Here we evaluated the possible associations between PGA, clinical characteristics and survival in an admixed GC Brazilian cohort. Methods: We included 112 GC pts diagnosed and treated at AC Camargo Cancer Center (São Paulo, Brazil) before 2013. The study was approved by local IRB. Genomic DNA was used for capture-based enrichment of a customized gene panel including 99 genes. Libraries were sequenced in the NextSeq 500 platform (Illumina), using paired-end reads (2x75bp). Ancestries were determined through a set of ancestry informative markers (AIMs), covered by target and off-target reads, described by Elhaik et al. (2014). Results: An average of 406 AIMs were recovered from the available samples, revealing average ancestries was as follows: 55.4% European, 27.7% Asian, 8.9% African; 8% of subjects were highly admixed (HA; < 50% of any ancestry). We found no association between PGA and age at diagnosis (p = 0.58), tumor location (p = 0.34), Lauren (p = 0.24) and staging (p = 0.68). There was an association between PGA and gender (p = 0.04) and a marginal association between PGA and EBV (p = 0.056). BRCA2 was the only gene enriched in the Asian subgroup, compared to the other groups combined (p = 0.009). The median follow-up time was 95 months. We found no differences in median overall survival (OS) (p = 0.4) or disease-free survival (DFS) (p = 0.6) according to PGA. The HA subgroup presented worst survival outcomes compared to the other groups aggregated (mOS 34m; 95%CI 5-80 x mOS 71m; 95% CI 44-85, respectively), but the difference was not statistically significant (HR 1,73; 95% CI 0.74-4.05; p = 0.2). Even for patients with > 75% AIMs for any given ancestry, we found no differences in OS between Europeans (n = 25; mOS 86m; 95%CI 80-NA), Asians (n = 22; mOS 83m; 95%CI 51-NA) and Africans (n = 5; mOS 67m; 95%CI 22-NA), p = 0.4. Conclusions: The most prevalent ancestries in this Brazilian GC cohort were European, followed by Asian and African. Although we found associations between ancestry and a few clinical aspects, PGA was not associated with survival.