title: Papillary thyroid carcinoma with nodular fasciitis-like stroma and β-catenin mutations should be renamed papillary thyroid carcinoma with desmoid-type fibromatosis.
abstract: Various histological variants of papillary thyroid carcinoma have been reported, some with clinical implications, some with peculiar, sometimes misleading morphologies. One of these rare and poorly characterized variants is papillary thyroid carcinoma with nodular fasciitis-like stroma, of which fewer than 30 cases have been documented, mostly as isolated reports. It is a dual tumor comprising a malignant epithelial proliferation that harbors typical features of conventional papillary thyroid carcinoma, admixed with a prominent mesenchymal proliferation resembling nodular fasciitis or fibromatosis. Thus, the terms papillary thyroid carcinoma with nodular fasciitis-like stroma and papillary thyroid carcinoma with fibromatosis-like stroma are used interchangeably; however, the former term suggests a self-limited and regressing disease, whereas the latter one suggests a recurrent and potentially aggressive one. Better genetic and ultrastructural characterization could lead to more appropriate terminology and management. We performed detailed clinicopathological and molecular analyses of two cases of PTC with prominent mesenchymal proliferation that developed in the thyroid gland of two male patients aged 34 and 48. In both cases, the epithelial component harbored a heterozygous somatic activating BRAF mutation (p.V600E). Also, in both cases, the mesenchymal component showed typical aberrant nuclear and cytoplasmic immunoreactivity for β-catenin and harbored a heterozygous somatic activating mutation in the corresponding CTNNB1 gene (p.S45P). This mutation has never been reported in thyroid stroma; in other tissues, it is typical of desmoid-type fibromatosis rather than nodular fasciitis-like stroma. We therefore propose that in cases of papillary thyroid carcinoma with a prominent mesenchymal component, mutations in CTNNB1 should be sought; when they are present, the term 'papillary thyroid carcinoma with desmoid-type fibromatosis' should be used. As the mesenchymal component of these tumors is not expected to concentrate radioactive iodine, special considerations apply to clinical evaluation and follow-up, which should be brought to the attention of the treating specialist.
authors.affiliation: Institute of Pathology, Lausanne University Hospital, Lausanne, Switzerland.
authors.forename: Caterina
authors.initials: C
authors.lastname: Rebecchini
authors.affiliation: Institute of Pathology, Lausanne University Hospital, Lausanne, Switzerland.
authors.forename: Antoine
authors.initials: A
authors.lastname: Nobile
authors.affiliation: Pathology Unit, IRCCS - Arcispedale Santa Maria Nuova, Reggio Emilia, Italy.
authors.forename: Simonetta
authors.initials: S
authors.lastname: Piana
authors.affiliation: Institute of Pathology, Lausanne University Hospital, Lausanne, Switzerland.
authors.forename: Rossella
authors.initials: R
authors.lastname: Sarro
authors.affiliation: Institute of Pathology, Lausanne University Hospital, Lausanne, Switzerland.
authors.forename: Bettina
authors.initials: B
authors.lastname: Bisig
authors.affiliation: Service of Endocrinology, Diabetes and Metabolism, Lausanne University Hospital, Lausanne, Switzerland.
authors.forename: Sykiotis P
authors.initials: SP
authors.lastname: Gerasimos
authors.affiliation: Institute of Pathology, Lausanne University Hospital, Lausanne, Switzerland.
authors.forename: Chiara
authors.initials: C
authors.lastname: Saglietti
authors.affiliation: Department of Visceral Surgery, Lausanne University Hospital, Lausanne, Switzerland.
authors.forename: Maurice
authors.initials: M
authors.lastname: Matter
authors.affiliation: Service of Endocrinology, Diabetes and Metabolism, Lausanne University Hospital, Lausanne, Switzerland.
authors.forename: Laura
authors.initials: L
authors.lastname: Marino
authors.affiliation: Institute of Pathology, Lausanne University Hospital, Lausanne, Switzerland.
authors.forename: Massimo
authors.initials: M
authors.lastname: Bongiovanni
mesh_terms: D000328:Adult; D002291:Carcinoma, Papillary / Q000235:genetics / Q000473:pathology*; D018222:Desmoid Tumors / Q000235:genetics / Q000473:pathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation; D017154:Stromal Cells / Q000473:pathology; D009626:Terminology as Topic; D013961:Thyroid Gland / Q000473:pathology*; D013964:Thyroid Neoplasms / Q000235:genetics / Q000473:pathology*; D051176:beta Catenin / Q000235:genetics
chemical_list: C495270:CTNNB1 protein, human; D051176:beta Catenin