Deciphering dual clinical entities associated with TP53 pathogenic variants: Insights from 53,085 HBOC panel analyses in French laboratories.

TP53 is included in most cancer predisposition multigene panels, especially those exploring Hereditary Breast and Ovarian Cancer (HBOC) predisposition. The purpose of this study was to define the contribution of TP53 pathogenic variants (PV) to the HBOC phenotype by collecting genotypes and phenotypes of 398 patients harboring a TP53 variant identified by 53,085 HBOC panel sequencing in 15 French laboratories. Heterozygous TP53 variants were identified in 0.44% of HBOC panels, evenly distributed between PV and VUS. Breast cancers associated with TP53 were predominantly triple positive, particularly Her2+ breast cancer, in situ cancer, or phyllodes tumors (p < 0.0001 for both). Interestingly, TP53 PV were identified across all ages in breast cancer patients, with enrichment before 36y. We demonstrated that null variants were linked with the HBOC phenotype, and missense variants, especially with a dominant negative effect, with the LFS phenotype (p = 0.0096). Patients with breast cancer harboring null variants displayed an earlier age of onset compared to missense (p = 0.0030). Surprisingly, we identified, in late-onset cancer patients, TP53 hotspot PV usually identified in classic LFS, which underlines variable penetrance. Thus, this study suggests the existence of two phenotypic entities associated with TP53 PV: clinical LFS and TP53-related breast cancer. The type of TP53 variant, as well as modifying factors reflected in family history, may influence these phenotypes, and both should be considered to define the clinical follow-up of patients and relatives.