Impact of age on genomic alterations and the tumor immune microenvironment in papillary thyroid cancer

Differentiated thyroid cancer in older adults has been linked to alterations in the mutational landscape and tumor immune cell infiltration that create a tumor-permissive microenvironment. We sought to determine the impact of age on genomic alterations and immune cell composition in papillary thyroid cancer (PTC). Genomic alterations, immune cell composition and clinical data were obtained using The Cancer Genome Atlas (TCGA) and computational immunogenomic analyses. Disease severity was recoded into 3 groups: Group A (T1-2N0M0), Group B (T1-3N1a-1bM0), and Group C (T4NxMx or TxNxM1). Histopathologic subtypes included conventional, follicular-variant, and tall cell variant PTC. Spearman’s rank correlation, ANOVA, t-test, and multivariable linear regression were performed. 470 PTC samples were retrieved from the TCGA portal with genomic alteration and immune cell composition data. TERT promoter alterations were more common in patients ≥ 65 years (26% vs 4%, p<0.0001). Tumor mutational burden increased with increasing age (r=0.463, p<0.0001). Increasing age was associated with decreased CD8+ T cells (r=-0.15, p=0.01) using CIBERSORT and decreased B cells (r=-0.13), CD8+ T cells (r=-0.19) and neutrophils (r=-0.14, p<0.05) using TIMER. Multivariate regression found that increasing age was independently associated with increased resting NK cells and resting dendritic cells, and decreased naïve B cells and CD8+ T cells (p<0.05). PTC tumors of older adults are characterized by increased TERT promoter alterations, increased tumor mutational burden, and a decreased cytotoxic CD8+ T and increased resting dendritic cell immune infiltrate. Further studies are needed to determine if these changes in immune cell infiltrate are associated with compromised outcomes.