Analysis of the Li-Fraumeni Spectrum Based on an International Germline TP53 Variant Data Set: An International Agency for Research on Cancer TP53 Database Analysis

IMPORTANCE: Li-Fraumeni syndrome is a cancer predisposition syndrome that is associated with a high, lifelong risk of a broad spectrum of cancers that is caused by pathogenic TP53 germline variants. A definition that reflects the broad phenotypic spectrum that has evolved since the gene discovery is lacking, and mechanisms leading to phenotypic differences remain largely unknown. OBJECTIVE: To define the phenotypic spectrum of Li-Fraumeni syndrome and conduct phenotype-genotype associations across the phenotypic spectrum. DESIGN, SETTING, AND PARTICIPANTS: We analyzed and classified the germline variant data set of the International Agency for Research on Cancer TP53 database that contains data on a cohort of 3034 persons from 1282 families reported in the scientific literature since 1990. We defined the term Li-Fraumeni spectrum to encompass (1) phenotypic Li-Fraumeni syndrome, defined by the absence of a pathogenic/likely pathogenic TP53 variant in persons/families meeting clinical Li-Fraumeni syndrome criteria; (2) Li-Fraumeni syndrome, defined by the presence of a pathogenic/likely pathogenic TP53 variant in persons/families meeting Li-Fraumeni syndrome testing criteria; (3) attenuated Li-Fraumeni syndrome, defined by the presence of a pathogenic/likely pathogenic TP53 variant in a person/family with cancer who does not meet Li-Fraumeni syndrome testing criteria; and (4) incidental Li-Fraumeni syndrome, defined by the presence of a pathogenic/likely pathogenic TP53 variant in a person/family without a history of cancer. Data analysis occurred from November 2020 to March 2021. MAIN OUTCOMES AND MEASURES: Differences in variant distribution and cancer characteristics in patients with a germline TP53 variant who met vs did not meet Li-Fraumeni syndrome testing criteria. RESULTS: Tumor spectra showed significant differences, with more early adrenal (n = 166, 6.5% vs n = 0), brain (n = 360, 14.17% vs n = 57, 7.46%), connective tissue (n = 303, 11.92% vs n = 56, 7.33%), and bone tumors (n = 279, 10.98% vs n = 3, 0.39%) in patients who met Li-Fraumeni syndrome genetic testing criteria (n = 2139). Carriers who did not meet Li-Fraumeni syndrome genetic testing criteria (n = 678) had more breast (n = 292, 38.22% vs n = 700, 27.55%) and other cancers, 45% of them occurring after age 45 years. Hotspot variants were present in both groups. Several variants were exclusively found in patients with Li-Fraumeni syndrome, while others where exclusively found in patients with attenuated Li-Fraumeni syndrome. In patients who met Li-Fraumeni syndrome genetic testing criteria, most TP53 variants were classified as pathogenic/likely pathogenic (1757 of 2139, 82.2%), whereas 40.4% (404 of 678) of TP53 variants identified in patients who did not meet the Li-Fraumeni syndrome genetic testing criteria were classified as variants of uncertain significance, conflicting results, likely benign, benign, or unknown. CONCLUSIONS AND RELEVANCE: The findings of this cohort study suggest that this new classification, Li-Fraumeni spectrum, is a step toward understanding the factors that lead to phenotypic differences and may serve as a model for other cancer predisposition syndromes.