Biphenotypic Branchioma: A Better Name Than Ectopic Hamartomatous Thymoma for a Neoplasm with HRAS Mutation
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ORIGINAL PAPER
Biphenotypic Branchioma: A Better Name Than Ectopic Hamartomatous Thymoma for a Neoplasm with HRAS Mutation Lester D. R. Thompson1 · Jeffrey Gagan2 · Antoine Washington3 · Rodney T. Miller4 · Justin A. Bishop2 Received: 1 December 2019 / Accepted: 14 January 2020 © This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply 2020
Abstract Ectopic hamartomatous thymoma is a rare neck lesion originally thought to represent a non-neoplastic hamartoma, even though thymic origin has been questioned, and there is uncertainty about whether the lesion is a neoplasm. We investigated the genetics by performing targeted next generation sequencing (NGS). Three cases were identified from the authors’ consultation files. A custom, targeted NGS panel including 1385 pan-cancer‐related genes was performed on all cases. Three patients included 2 males and 1 female, aged 50, 58 and 70 years, respectively (mean 59.3 years), with tumors arising in the low anterior neck. All cases showed classical histologic features of EHT, with one case showing intraductal carcinoma in association with the EHT. By targeted NGS, one case harbored a hotspot HRAS mutation (p.Gln61Lys), while the other two cases only showed non oncogenic variants. Dual mesoderm and endoderm derivation/differentiation (biphenotypic) has been previously recognized, with epithelial and myoepithelial components, and arising from the apparatus contributing to neck development (branchial apparatus). Thus, EHT has been shown to have genetic alterations in HRAS. These findings, without evidence of thymic derivation or an ectopic tissue location, strongly support that EHT is a true neoplasm. The name biphenotyic branchioma more correctly reflects the true nature of this dual mesoderm and endoderm derived tumor occurring in the lower neck. Keywords Ectopic hamartomatous thymoma · Biphenotypic branchioma · Carcinoma · Branchial pouch · NGS · Neoplasm
Introduction Ectopic hamartomatous thymoma (EHT) is a rare benign neoplasm that almost exclusively occurs in the lower neck of middle-aged patients with a remarkable male predominance as reported in a recent review the literature [1]. These lesions show an admixture of spindle cells, epithelial islands, and adipocytes. Since the original unifying descriptions [2–4], there has been continued discussion about nomenclature. The term biphenotypic branchioma was recently introduced
* Lester D. R. Thompson [email protected] 1
Department of Pathology, Southern California Permanente Medical Group, Woodland Hills Medical Center, 5601 De Soto Avenue, Woodland Hills, CA 91365, USA
2
Department of Pathology, University of Texas Southwestern Medical Center, Dallas, TX, USA
3
Trinity Pathology Associates, Tyler, TX, USA
4
ProPath, Dallas, TX, USA
as a better name for this lesion [1]. There has been no definitive genetic evaluation of this lesion and thus we sought to further understand the genetic features of this tumor by performing next generation s
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