AbstractBackgroundTP53 is the most commonly mutated gene across all cancer types. R175H mutation was considered structural mutation where the mutation causes misfolding of the protein and leads to a significant conformational alterations within p53's DNA binding domain. The aim of this study was to explain the reason why R175H worse the response to immunotherapy by analyzing tumor immune microenvironment through the expression of immune cells and PD‐1.Materials and MethodsPatients diagnosed with metastatic carcinoma, including colorectal cancer (CRC), breast cancer (BRCA), gastric cancer (GC), non‐small cell lung cancer (NSCLC), and 20 other cancer types, treated in a palliative setting at Samsung Medical Center between October 2019 and April 2021, were enrolled. Of these patients, those who underwent TDS analysis (TruSight™ Oncology 500 assay [TSO 500]) were finally analyzed.ResultsOf 1770 patients, 1012 (57.2%) harbored genetic alterations in TP53. All mutations were single nucleotide variants (SNVs), and the most frequent SNV was R175H (n= 84, 7.5%) which was known as one of the most common hotspot TP53 mutation. The overall survival of patients with TP53 R175H mutations was significantly worse following chemotherapy (606 vs. 456 days,p< 0.001) or immunotherapy (822 vs. 350 days,p< 0.001) compared to those with TP53 mutation in other loci. RNA sequencing indicated that the immune response‐related pathways were downregulated in tumors harboring TP53 R175H mutation. Moreover, the expression of CD8(+) T cells PD‐1 were lowered in R175H mutation tumors. In the analysis of TP53 structural domain, compared to those having TP53 mutation in other domain, patients with mutations occurring in the nuclear exporter signal (NES) and E4F1‐binding domains had significantly worse overall survival following chemotherapy (NES: 606 vs. 451 days,p= 0.043; E4F1: 606 vs. 469 days,p= 0.046) and immunotherapy (NES: 822 vs. 403 days,p< 0.001; E4F1: 822 vs. 413 days,p< 0.001). In addition, tumors with TP53 mutation and co‐existing copy number amplification of CCND1, FGF4, and FGF19 in chromosome 11 conferred worse prognosis than those with only TP53 mutation (p< 0.050).DiscussionEach TP53 mutations indicated differential treatment outcomes following chemotherapy or immunotherapy in patients with metastatic cancer. Functional analysis including RNASeq suggested that TP53 mutation downregulated immune response.ConclusionOverall, we found eachTP53mutation to indicate different prognoses in patients with metastatic tumors undergoing chemotherapy and ICI treatment. Further validations, including a prospective cohort study or a functional study, would be particularly valuable in advancing the knowledge on this aspect and developing improved prognostic parameters.