Characterization of tumor mutation load (TML) in solid tumors.

Abstract

11517 Background: Rapid advances in immunotherapy have created a need for biomarkers to improve patient treatment selection. TML is proposed as a potential predictive biomarker due to its association with tumor immunogenicity. Methods: TML was assessed in 8020 tumors from 14 different cancers using somatic nonsynonymous missense mutations sequenced with a 592-gene panel. High TML was set at ≥ 17 mutations per megabase (mt/MB) based on an established concordance ( > 99%) with MSI-High in colorectal cancer (CRC). Results: Mean TML was highest in melanoma (Mel; 21 mt/MB), NSCLC (11 mt/MB), and bladder cancer (BLC; 11 mt/MB), whereas prostate cancer (PC), pancreas adenocarcinoma (PA), and renal cell carcinoma (RCC) had the lowest levels (all 6 mt/MB). High TML was seen most frequently in Mel (36%), NSCLC (15%), BLC (15%), and anal cancer (SCCA; 9%); and least frequently in PA (1.6%) and RCC (0.5%). Primary NSCLC carried lower TML than its brain metastases (11 vs. 16 mt/MB, p < 0.001). Older age was associated with higher TML in Mel (p = 0.001), CRC (p = 0.009), breast cancer (BC; p = 0.01), and NSCLC (p = 0.02). Higher TML was seen in males than in females for Mel (p = 0.002) and NSCLC (p < 0.001). Presence of mutations in oncogenic driver genes such as EGFR, ALK, ROS1 RET fusions, cMET exon 14 skipping correlated with lower TML in NSCLC (6.9 vs. 12 mt/MB, p < 0.001), as did BRAF and NRAS mutations in Mel (17 vs. 26, p = 0.003). Conversely, mutations in tumor suppressor genes such as ARID1A (CRC, NSCLC, and BLC) and NF1 (BC, CRC, Mel, BLC, and NSCLC) were associated with higher TML (p < 0.05). MSI-high was correlated with high TML in CRC and gastric cancers (p < 0.05). Conclusions: TML varied significantly among different cancers. High TML was associated with older age, absence of oncogenic mutations and presence of tumor suppressor gene mutations. Future studies will assess the impact of TML on clinical outcome and establish its role in selecting patients for immunotherapy. [Table: see text]