The neoantigen landscape of the coding and noncoding cancer genome space

Tumor mutation burden (TMB) is a measure to predict patient responsiveness to immune checkpoint immunotherapy since with increased mutation frequency, the likelihood of a greater neoantigen burden is increased. Although neoantigen prediction tools exist, tumor neoantigen burden (TNB) has not been adopted as measures to predict immunotherapy response. With both measures, current guidelines are limited to the coding regions, but ectopic expression of sequences in the noncoding space may potentially be a source of neoantigens. Here we analyzed a pan-cancer cohort of 574 advanced disease stage patients with whole genome and transcriptome sequencing to report mutation burden and neoantigen counts within the coding and noncoding regions. We evaluated the efficacy of TNB, reported as tumor neoantigen counts (TNC), including neoantigens derived from the expression of noncoding regions, compared to TMB as a predictor of response to immunotherapy for 80 patients who had received treatment. We found that TMB was the best predictor of response to immunotherapy, whereas expression derived TNC from the noncoding regions did not improve prediction of response. Therefore, there is minimal benefit in extending the calculation of TNC to the noncoding space for the purposes of predicting response. However, it is likely that there is a wealth of neoantigens derived from the noncoding space that may impact patient outcomes and treatments.