Prevalence of germline mutations in the TP53 gene in patients with early-onset breast cancer in the Mexican population

BACKGROUND: Heterozygous germline TP53 gene mutations result in Li-Fraumeni Syndrome (LFS). Breast cancer (BC) is the most frequent tumor in young women with LFS. An important issue related to BC in the Mexican population is the average age at diagnosis, which is approximately 11 years younger than that of patients in the United States (U.S.) and Europe. The aim of this study was to determine the prevalence of germline mutations in TP53 among young Mexican BC patients. METHODS: We searched for germline mutations in the TP53 gene using targeted next-generation sequencing (NGS) in 78 BC patients younger than 45 years old (yo) who tested negative for BRCA1/2 mutations. A group of 509 Mexican women aged 45yo or older without personal or family BC history (parents/grandparents) was used as a control. RESULTS: We identified five patients with pathogenic variants in the TP53 gene, equivalent to 6.4% (5/78). Among patients diagnosed at age 36 or younger, 9.4% (5/55) had pathogenic TP53 mutations. Three of these variants were missense mutations (c.844C > T, c.517G > A, and c.604C > T), and the other two mutations were frameshifts (c.291delC and c.273dupC) and had not been reported previously. We also identified a variant of uncertain clinical significance (VUS), c.672G > A, which causes a putative splice donor site mutation. All patients with TP53 mutations had high-grade and HER2-positive tumors. None of the 509 patients in the healthy control group had mutations in TP53. CONCLUSIONS: Among Mexican BC patients diagnosed at a young age, we identified a high proportion with germline mutations in the TP53 gene. All patients with the TP53 mutations had a family history suggestive of LFS. To establish the clinical significance of the VUS found, additional studies are needed. Pathogenic variants of TP53 may explain a substantial fraction of BC in young women in the Mexican population. Importantly, none of these mutations or other pathological variants in TP53 were found in the healthy control group.