Branchioma: immunohistochemical and molecular genetic study of 23 cases highlighting frequent loss of retinoblastoma 1 immunoexpression.

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.

Branchioma with a nested/organoid morphology: molecular profiling of a distinctive potentially misleading variant and reappraisal of potential relationship to CD34-positive/Rb1-deficient tumors of the neck.

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.

Molecular Profiling of Salivary Oncocytic Mucoepidermoid Carcinomas Helps to Resolve Differential Diagnostic Dilemma With Low-grade Oncocytic Lesions.

Oncocytic mucoepidermoid carcinoma (OMEC) is a rare but diagnostically challenging variant of mucoepidermoid carcinoma (MEC). OMEC is notable for differential diagnostic considerations that are raised as a result of overlap with other benign and low-grade oncocytic salivary gland tumors. Diffuse and strong immunoreactivity of p63 protein may be useful in distinguishing OMEC from its mimics. However, focal p63 staining can be present in benign oncytomas. Presence of mucin-containing cells, mucinous cystic formation, and foci of extravasated mucin are considered a hallmark of MEC. True mucocytes may be, however, very few and hardly discernable in OMECs. Recent evidence has shown that most MECs harbor gene fusions involving MAML2. A retrospective review of archived pathology files and the authors' own files was conducted to search for "low-grade/uncertain oncocytic tumor," "oncocytoma," and "oncocytic carcinoma" in the period from 1996 to 2019. The tumors with IHC positivity for p63 and/or p40, and S100 negativity, irrespective of mucicarmine staining, were tested by next-generation sequencing using fusion-detecting panels to detect MAML2 gene rearrangements. Two index cases from consultation practice (A.S. and A.A.) of purely oncocytic low-grade neoplasms without discernible mucinous cells showed a CRTC1-MAML2 fusion using next-generation sequencing, and were reclassified as OMEC. In total, 22 cases of oncocytic tumors, retrieved from the authors' files, and from the Salivary Gland Tumor Registry, harbored the MAML2 gene rearrangements. Presence of mucocytes, the patterns of p63 and SOX10 immunopositivity, and mucicarmine staining were inconsistent findings. Distinguishing OMEC devoid of true mucinous cells from oncocytoma can be very challenging, but it is critical for proper clinical management. Diffuse and strong positivity for p63 and visualization of hidden mucocytes by mucicarmine staining may be misleading and does not always suffice for correct diagnosis. Our experience suggests that ancillary studies for the detection of MAML2 rearrangement may provide useful evidence in difficult cases.

A Clinicopathological Study of 29 Spitzoid Melanocytic Lesions With ALK Fusions, Including Novel Fusion Variants, Accompanied by Fluorescence In Situ Hybridization Analysis for Chromosomal Copy Number Changes, and Both TERT Promoter and Next-Generation Sequencing Mutation Analysis.

ALK-fused spitzoid neoplasms represent a distinctive group of melanocytic lesions. To date, few studies addressed genetic and chromosomal alterations in these lesions beyond the ALK rearrangements. Our objective was to study genetic alterations, including ALK gene fusions, telomerase reverse transcriptase promoter (TERT-p) mutations, chromosomal copy number changes, and mutations in other genes. We investigated 29 cases of Spitz lesions (11 Spitz nevi and 18 atypical Spitz tumors), all of which were ALK immunopositive. There were 16 female and 13 male patients, with age ranging from 1 to 43 years (mean, 18.4 years). The most common location was the lower extremity. Microscopically, all neoplasms were polypoid or dome shaped with a plexiform, predominantly dermally located proliferation of fusiform to spindled melanocytes with mild to moderate pleomorphism. The break-apart test for ALK was positive in 17 of 19 studied cases. ALK fusions were detected in 23 of 26 analyzable cases by Archer FusionPlex Solid Tumor Kit. In addition to the previously described rearrangements, 3 novel fusions, namely, KANK1-ALK, MYO5A-ALK, and EEF2-ALK, were found. Fluorescence in situ hybridization for copy number changes yielded one case with the loss of RREB1 among 21 studied cases. TERT-p hotspot mutation was found in 1 of 23 lesions. The mutation analysis of 271 cancer-related genes using Human Comprehensive Cancer Panel was performed in 4 cases and identified in each case mutations in several genes with unknown significance, except for a pathogenic variant in the BLM gene. Our study confirms that most ALK fusion spitzoid neoplasms can be classified as atypical Spitz tumors, which occurs in young patients with acral predilection and extends the spectrum of ALK fusions in spitzoid lesions, including 3 hitherto unreported fusions. TERT-p mutations and chromosomal copy number changes involving 6p25 (RRB1), 11q13 (CCND1), 6p23 (MYB), 9p21 (CDKN2A), and 8q24 (MYC) are rare in these lesions. The significance of mutation in other genes remains unknown.

Renal small cell oncocytoma with pseudorosettes A histomorphologic, immunohistochemical, and molecular genetic study of 10 cases.

A cohort of a heretofore not described rare subtype of renal oncocytoma, small cell oncocytoma with pseudorosettes is presented. Patients were 6 women and 4 men with ages ranging from 51 to 76 years. The tumors displayed areas composed of small cells ("oncoblasts") featuring scant cytoplasm and small, round monomorphic nuclei. The small cell areas constituted 15% to 60% of the total tumor volume (mean, 28.5%; median, 22.5%). No necrosis or mitotic activity was discerned. All tumors also contained areas composed of characteristic oncocytes comprising 40% to 85% of the total tumor volume. In all cases, a varying number of pseudorosettes were identified. The pseudorosettes were composed of small globules of (periodic acid-Schiff-positive) hyaline basal membrane-like material surrounded by small "oncoblastic" cells. The immunohistochemical profile was variable, including at least focal positivity for AE1-3 (10/10), cytokeratin 7 (7/10), epithelial membrane antigen (10/10), c-kit (6/10), antimitochondrial antigen (MIA;10/10), PAX-2 (9/10), AMACR (racemase;6/10), CD10 (5/10), parvalbumin (8/10), vimentin (6/10), claudin 7 (10/10), and claudin 8 (3/10). No immunoreactivity for carbonic anhydrase 9, HMB-45, S-100A1, and TFE3 was documented. We found no differences in the immunophenotype in the small cell oncocytes/oncoblasts that formed pseudorosettes and those that did not. However, there were differences in the immunohistochemical profile of classic oncocytes and small cell oncocytes/oncoblasts. Using array comparative genomic hybridization, no chromosomal changes were identified in any of the cases examined (n = 3). No numerical changes of chromosomes 7 and 17 were revealed on fluorescence in situ hybridization analysis (n = 3). In conclusion, we herein present the first study on small cell renal oncocytomas with formation of pseudorosettes. This is a rare subtype of oncocytoma, which may, especially on a core biopsy, present differential diagnostic difficulties. The immunohistochemical profile of these tumors is variable and differs in significant respects from that of conventional renal oncocytoma. Awareness of this entity and its immunohistochemical variability should help in distinguishing this rare tumor from malignant tumors with similar (small cell) histomorphologic features. All tumors behaved in a benign fashion during follow-up (mean, 3.1 years; median, 1 year).

Massive squamous metaplasia of the thyroid gland-- report of three cases.

Three cases of massive squamous cell metaplasia in Hashimoto's thyroiditis are reported. The patients were two men and one woman aged 24, 52, and 55 years, respectively. In all three patients, the glandular parenchyma was replaced by hypocellular fibrous tissue with scattered chronic inflammatory infiltrate. Follicular cells were almost absent; the majority of residual epithelial cells formed squamous nests that were partly solid and partly cystic. There were three types of epithelial cells - squamous, basaloid, and follicular, with oncocytic differentiation. The squamous and basaloid cells showed strong positivity high molecular weight (HMW) cytokeratin, moderate to strong expression of galectin-3 (2/3), and nuclear expression of p63 protein (2/3). The staining pattern of p63 was identical to that of HMW, with predominant positivity at the periphery of cell nests. In one case, weak but unequivocal positivity of thyroid transcription factor-1 also was present. We believe that metaplasia was caused by Hashimoto's thyroiditis. The cases presented here are extremely rare, and only two convincing similar cases have been reported in the English literature so far. They may represent a diagnostic pitfall and should not be misdiagnosed as a malignancy, in particular as squamous cell or mucoepidermoid carcinoma.

Thread-like bridging strands: a morphologic feature present in all adenomatoid tumors.

Adenomatoid tumor (AT) is a benign, relatively rare neoplasm occurring primarily in the genital tract of both genders. Histologically, ATs were composed of fibrous tissue, which are separated by numerous slit-like and pseudotubular spaces. Peculiar "thread-like bridging strands" (TBS) crossing the pseudotubular spaces are typical morphologic feature. In this study, the frequency of occurrence of these TBS within a large series of ATs in various organs was examined. Sixty-nine cases were included in our study. Twenty-eight cases occurred in women, 41 cases in men. Tumors were located in the myometrium, fallopian tube, ovary, epididymis, tunica albuginea, and testicular parenchyma. Tumor size ranged from 0.8 to 8.2 cm (mean, 2.7 cm). TBS were found in 100% of cases. Presence of thin intraluminal TBS within ATs was a constant morphologic feature independently on gender and localization of the lesions. Ultrastructurally, they were always formed by apposition of attenuated cytoplasm of two adjacent mesothelial cells. In our opinion, TBS are morphologically very specific for ATs and we are not aware of any other epithelial structure in any organ demonstrating as appearance similar to these TBS of ATs.