Prevalence and functional consequence of TP53 mutations in pediatric adrenocortical carcinoma: a children's oncology group study

Abstract

Purpose: Adrenocortical carcinoma (ACC) is a rare pediatric malignancy. It occurs in excess among individuals with the Li-Fraumeni syndrome, which results primarily from germline mutations in the TP53 gene. Prior series exploring frequencies of germline TP53 mutation among children with ACC have been small, geographically limited, or subject to referral bias. The functional consequence of mutations has not been related to phenotype. We provide a genotype-phenotype analysis of TP53 mutations in pediatric ACC and propose a model for tissue-specific effects based on adrenocortical ontogeny.

Patients and methods: Eighty-eight consecutive, unrelated children with ACC, unselected for family history, underwent germline TP53 sequencing. Rate and distribution of mutations were identified. Functional analysis was performed for novel TP53 variants. Correlation with the International Agency for Research on Cancer p53 database further delineated mutational distribution, association with family history, and risk for multiple primary malignancies (MPMs).

Results: Germline mutations were present in 50% of children. These mutations did not correspond to the conventional hotspot mutations. There was a wide range of mutant protein function. Patients bearing alleles encoding protein with higher functionality were less likely to have a strong family cancer history, whereas those with greater loss of function had MPMs and/or positive family history. In patients with MPMs, ACC was the most frequent initial malignancy. Finally, we demonstrated age-dependent rates of TP53 mutation positivity.

Conclusion: TP53 mutations are prevalent in children with ACC but decline with age. Mutations result in a broad spectrum of functional loss. Effect of individual mutations may predict carrier and familial disease penetrance with potentially broad implications for clinical surveillance and counseling.

Fig 1.

Distribution of germline TP53 mutation type in (A) the current cohort, (B) all reported pedigrees with adrenocortical carcinoma (ACC) in the International Agency for Research on Cancer (IARC) database, and (C) all pedigrees (all tumor types) in the IARC database. COG, Children's Oncology Group.

Fig 2.

(A) Functional activity of TP53 variants expressed in H1299 cells as determined by transactivation of TP53-responsive luciferase reporter (or a control reporter with point mutations in the response element which abolish TP53 binding [MutBS], Data Supplement). Expression of TP53 was confirmed by Western blot. C275X and Ins933a variants result in truncated proteins with faster migration. Vinculin staining demonstrates equal protein loading. All lanes except C275X and Ins933a demonstrate a full-length TP53 (53 kDa) and a smaller breakdown product. Loss-of-function alleles are associated with higher expression (presumably mediated by lack of negative feedback). (B) Data in panel A ranked based on activity and correlated with clinical presentation. Black rectangles indicate a family history consistent with Li-Fraumeni syndrome (LFS)/Li-Fraumeni–like syndrome (LFLS). White rectangles indicate absence of a significant family history in a complete pedigree containing three or more generations. Hatched rectangles indicate insufficient data to establish or exclude a family history of cancer predisposition. MPM, multiple primary malignancies; MR ACC, multiply recurrent adrenocortical carcinoma; mutBS, mutated TP53 binding site; WT, wild type.

Fig 3.

Colony reduction assays. Fourteen days after transfection, plates were stained with crystal violet and the remaining colony numbers were quantified manually. Representative plates of (A) vector, (B) wild-type (WT) TP53-transfected, or (C) TP53^R273H-transfected cells. R273H is a hotspot mutation with minimal residual TP53 function. (D) Quantification of data for all alleles is shown. MutBS, mutated TP53 binding site.

Fig 4.

Prevalence of germline TP53 mutations based on age at diagnosis. Aggregate data from this study, as well as those of Herrmann et al and Raymond et al are included in this representation. Percentage of individuals with TP53 germline mutations is indicated.