Can TP53-mutant follicular adenoma be a precursor of anaplastic thyroid carcinoma?

Mutations of the TP53 tumor suppressor gene are highly prevalent in thyroid anaplastic carcinomas (AC) but are also reported in some well-differentiated cancers and even in benign adenomas. The natural history of TP53-mutant adenomas and whether they may represent a precursor for well-differentiated cancer or AC is largely unknown. Similarly, the frequency of TP53 mutations in thyroid nodules found on routine molecular analysis of fine-needle aspiration (FNA) samples is not established. A database on 44,510 FNA samples from thyroid nodules with predominantly indeterminate cytology tested using ThyroSeq v3 was reviewed to identify TP53-mutant cases and analyze their genetic profile and available clinicopathological findings. Among 260 (0.6%) selected thyroid nodules, 36 had an isolated TP53 mutation and 224 carried a combination of TP53 with other genetic alterations. No significant difference was observed between these groups with respect to patient age, gender, nodule size, and spectrum of TP53 mutations. Histopathologically, 86% of the resected nodules with isolated TP53 mutations were benign (mostly adenomas), whereas 82% of nodules carrying TP53 mutations co-occurring with other alterations were cancers (P = 0.001), including de-differentiated AC. TP53-mutant benign tumors and well-differentiated cancers often had scattered single neoplastic cells with bizarre nuclei resembling those comprising AC. Our study demonstrates that a small but distinct proportion of thyroid nodules carry a TP53 mutation, either as a single genetic event or in combination with other alterations. While the latter is mostly cancers prone to dedifferentiation, there is at least a theoretical possibility that TP53-mutated adenomas may represent a precursor for such cancers, including AC.

Automated summary

Mutations of the TP53 gene are common in thyroid anaplastic carcinomas and can also be found in benign adenomas. Our study found that thyroid nodules with TP53 mutations either alone or in combination with other alterations may represent precursors for well-differentiated cancers, including anaplastic carcinomas.