Abstract
PURPOSE: Tumor Protein 53 (p53) expressed from gene TP53 is a seminal tumor suppressor. We aimed to characterize mutational and nonmutational mechanisms of p53 dysfunction in myelodysplastic syndromes (MDS) and to investigate their clinical effect. PATIENTS AND METHODS: We analyzed a cohort of 6,204 patients with MDS and subsets of patients with available information on RNA sequencing of tumor cells (n = 109), high-dimensional phenotype of immune cells (n = 77), and multiomics analysis (RNA sequencing and proteomics) on single cells (n = 15). An independent validation was performed on 914 patients. RESULTS: Biallelic TP53 inactivation was a powerful driver of disease progression and identified high-risk patients, regardless of variant allele frequency. Monoallelic and biallelic inactivation represent disease stages occurring as a multihit process in MDS with TP53 mutations, thus potentially refining the optimal timing of therapeutic interventions in these patients. We identified a subset of MDS (5%) characterized by TP53 wild-type and hyperexpression of abnormal p53 protein in bone marrow progenitors that exhibit dismal outcome. These patients presented upstream p53 signaling aberrations in Pi3K cascade; RAS, WNT, and NF-KB pathways; and MDM2 gene amplification, together with a downstream dysregulation of p53 targets. MDS with p53 dysfunction displayed a distinct immune dysregulation involving myeloid-derived inflammation and impaired antigen presentation, which may be a driver of their poor prognosis and provide the groundwork for innovative immunotherapies. CONCLUSION: The identification of nonmutational p53 dysfunction in MDS may lay the foundation for a mechanistic classification of myeloid neoplasms, moving beyond a purely molecular stratification. The recognition of patients with p53 dysfunction is relevant to provide correct disease-risk assessment and interventions, as well as to refine the design of clinical trials.