Branchioma is an uncommon benign neoplasm with an adult male predominance, typically occurring in the lower neck region. Different names have been used for this entity in the past (ectopic hamartomatous thymoma, branchial anlage mixed tumor, thymic anlage tumor, biphenotypic branchioma), but currently, the term branchioma has been widely accepted. Branchioma is composed of endodermal and mesodermal lineage derivatives, in particular epithelial islands, spindle cells, and mature adipose tissue without preexistent thymic tissue or evidence of thymic differentiation. Twenty-three branchiomas were evaluated morphologically. Eighteen cases with sufficient tissue were assessed by immunohistochemistry, next-generation sequencing (NGS) using the Illumina Oncology TS500 panel, and fluorescence in situ hybridization (FISH) using an RB1 dual-color probe. All cases showed a biphasic morphology of epithelial and spindle cells with intermingled fatty tissue. Carcinoma arising in branchioma was detected in three cases. The neoplastic cells showed strong AE1/3 immunolabeling (100%), while the spindle cells expressed CD34, p63, and SMA (100%); AR was detected in 40-100% of nuclei (mean, 47%) in 14 cases. Rb1 showed nuclear loss in ≥ 95% of neoplastic cells in 16 cases (89%), while two cases revealed retained expression in 10-20% of tumor cell nuclei. NGS revealed a variable spectrum of likely pathogenic variants (n = 5) or variants of unknown clinical significance (n = 6). Loss of Rb1 was detected by FISH in two cases. Recent developments support branchioma as a true neoplasm, most likely derived from the rudimental embryological structures of endoderm and mesoderm. Frequent Rb1 loss by immunohistochemistry and heterozygous deletion by FISH is a real pitfall and potential confusion with other Rb1-deficient head and neck neoplasms (i.e., spindle cell lipoma), especially in small biopsy specimens.

• Klíčová slova
• And neck, Branchioma, CD34, Ectopic hamartomatous thymoma, Head, RET, Retinoblastoma 1,
• MeSH
• branchiom * patologie   MeSH
• dospělí MeSH
• hybridizace in situ fluorescenční MeSH
• lidé MeSH
• molekulární biologie MeSH
• nádory brzlíku * MeSH
• nádory glandulární a epitelové * MeSH
• nádory měkkých tkání * patologie   MeSH
• nádory sítnice * MeSH
• retinoblastom * genetika   patologie   MeSH
• thymom * MeSH
• Check Tag
• dospělí MeSH
• lidé MeSH
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH

Two benign adenomatous lesions are commonly recognized within the sinonasal tract, namely respiratory epithelial adenomatoid hamartoma (REAH) and seromucinous hamartoma (SH). We present 10 hitherto unrecognized benign polypoid nasal and sinonasal tumoriform lesions having in average 3.6 cm in largest dimension, which are histogenetically related to SH and REAH. In addition to typical structures of REAH and SH, these lesions contained an additional characteristic and slightly atypical adenomatous component, which we termed atypical sinonasal glands arising in SH (ASGSH). ASGSH often produced deep red colored secretion with peripheral clearing similar to that seen in thyroid follicles. In contrast to SH, ASGSH was endowed by both secretory and myoepithelial layers and had mostly angulated shapes with snout-like protrusions into the lumens. Both layers were formed by an irregular, disorganized, and often incomplete cell lining, which had slightly atypical cytological features without mitoses. In 3 cases, ASGSHs revealed sebaceous differentiation, and in 3 cases the stroma produced a well-differentiated cartilage. Neoplastic nature of ASGSH was supported by finding of various mutations as revealed by next generation sequencing in five cases. In two cases each, we found identical mutations in BRAF gene (Val600Glu), and RET gene (Arg912Trp), respectively and in one case FAT1 gene alteration (Pro1665Leu).

• Klíčová slova
• Atypical adenomatous lesions arising in REAH/seromucinous hamartoma, REAH, Respiratory adenomatoid hamartoma, Sebaceous differentiation, Seromucinous hamartoma,
• Publikační typ
• časopisecké články MeSH

Branchioma (previously called ectopic hamartomatous thymoma, branchial anlage mixed tumor, or thymic anlage tumor) is a rare lower neck lesion with an adult male predominance and an uncertain histogenesis. Except for 4 cases, all branchiomas described in the literature were benign. Recently, HRAS mutation was detected in one case, but still little is known about the molecular genetic background of this rare entity. We herein report the histological, immunohistochemical, and molecular genetic analysis of a branchioma with a nested/organoid (neuroendocrine-like) morphology in a 78-year-old man. Histology revealed classical branchioma areas merging with nested/organoid cellular component lacking conventional features of malignancy. Immunohistochemistry was positive for high-molecular-weight cytokeratins. CD34 was expressed in the spindle cell component. Moreover, the tumor cells showed near-complete loss of retinoblastoma (RB1) expression (<1% of cells positive). All neuroendocrine markers (synaptophysin, chromogranin, and INSM1) were negative. Next-generation sequencing (TSO500 Panel) revealed 5 pathogenic/likely pathogenic mutations including 1 mutation in KRAS and 2 different mutations in each of MSH6 and PTEN. FISH and DNA sequencing were negative for RB1 gene alterations. To our knowledge, this is the first report of a branchioma showing misleading nested/organoid morphology and the first report on Rb1 immunodeficiency in this entity, in addition to multiple gene mutations revealed by NGS.

• Klíčová slova
• Androgen receptor, Branchioma, CD34, Ectopic hamartomatous thymoma, Head and neck, Neuroendocrine carcinoma-like, RB1 gene, Retinoblastoma,
• MeSH
• branchiom * patologie   MeSH
• lidé MeSH
• nádory měkkých tkání * MeSH
• nádory sítnice * MeSH
• organoidy patologie   MeSH
• represorové proteiny MeSH
• retinoblastom * genetika   patologie   MeSH
• senioři MeSH
• Check Tag
• lidé MeSH
• mužské pohlaví MeSH
• senioři MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• kazuistiky MeSH
• Názvy látek
• INSM1 protein, human MeSH Prohlížeč
• represorové proteiny MeSH

We report a case of a 67-year-old male patient with a sinonasal tumor that showed areas of classic biphenotypic sinonasal sarcoma (BSNS) which in some sections sharply transitioned into high-grade rhabdomyosarcoma. Immunohistochemically, the conventional BSNS parts showed S100 protein, SMA, PAX7, and focal MyoD1 expression, whereas desmin and myogenin were negative. In contrast, the cells in high-grade areas expressed desmin, MyoD1, myogenin, and PAX7, while being negative for S100 protein and SMA. Using the Archer FusionPlex assay, the classical PAX3::MAML3 gene fusion was detected. FISH for PAX3 and MAML3 confirmed a break of these genes in both components. Despite aggressive therapy, the tumor progression resulted in the patient's death. The herein presented case, together with 2 previously published cases of BSNS with high-grade transformation, helps to better understand this novel phenomenon. Although the risk for such transformation appears low, it has important clinical and diagnostic implications which are discussed.

• Klíčová slova
• Biphenotypic sinonasal sarcoma, High-grade transformation, PAX3::MAML3, Rhabdomyosarcoma,
• MeSH
• alveolární rhabdomyosarkom * MeSH
• desmin MeSH
• imunohistochemie MeSH
• lidé středního věku MeSH
• lidé MeSH
• myogenin MeSH
• nádorové biomarkery genetika   MeSH
• nádory měkkých tkání * genetika   MeSH
• nádory vedlejších dutin nosních * patologie   MeSH
• proteiny S100 MeSH
• rhabdomyosarkom * genetika   MeSH
• sarkom * genetika   MeSH
• trans-aktivátory MeSH
• transkripční faktor PAX3 genetika   MeSH
• Check Tag
• lidé středního věku MeSH
• lidé MeSH
• mužské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• kazuistiky MeSH
• Názvy látek
• desmin MeSH
• MAML3 protein, human MeSH Prohlížeč
• myogenin MeSH
• nádorové biomarkery MeSH
• PAX3 protein, human MeSH Prohlížeč
• proteiny S100 MeSH
• trans-aktivátory MeSH
• transkripční faktor PAX3 MeSH