MYB Rearrangement Research Articles

Immunohistochemical marker profiles for the differentiation of collagenous spherulosis from adenoid cystic carcinoma of the breast

Collagenous spherulosis (CS) is a rare breast lesion of unknown histogenesis. Adenoid cystic carcinoma (ACC) is a rare basal-like breast carcinoma with low histological grade. CS is a benign lesion but resembles ACC. Both lesions show a similar histomorphology and feature bilineage differentiation. This study compared immunohistochemical markers in CS and ACC.We compiled n = 13 CS cases and n = 18 mammary ACCs. Fourteen marker proteins (ER, PR, HER2, GATA3, CK7, E-cadherin, CD117, CK5/14, p40, p63, SMA, CD10, calponin, P-cadherin) were evaluated by immunohistochemistry (IHC). MYB rearrangement, a common alteration in ACC, was assessed by fluorescence in situ hybridization.Patient age ranged between 40-60 years for CS lesions and 30–90 years for ACCs. 7/13 (54%) CS cases harbored a lobular carcinoma in situ (LCIS) in the luminal component. One CS/LCIS lesion occurred in a carrier of a pathogenic germline variant in CDH1/E-cadherin. MYB rearrangement was detected in 0/11 (0%) CS and 6/16 (37%) ACC cases (P = 0.054). CS was associated with expression of ER in the luminal component (P < 0.001), E-cadherin loss in the luminal component (P = 0.045), and expression of CD10 and calponin in the basal component (P < 0.001). Furthermore, CS was associated with GATA3 expression in the luminal component (12/13 [92%] versus 5/18 [27%], P < 0.001).In summary, IHC for GATA3 and E-cadherin may contribute to the differential diagnosis between CS and ACC, although these markers are not exclusively expressed in either lesion. Histologic evaluation has to take into account that CS is frequently colonized by LCIS, requiring thorough correlation of histomorphology and immunohistochemical features.

Adenoid Cystic Carcinoma of the Vulva and Vagina: A Clinicopathologic, Immunohistochemical, and Molecular Characterization of Five Cases.

Adenoid cystic carcinoma (ACC) is a rare neoplasm most frequently observed in the salivary glands, that can occur in other organs, including the vulva and vagina. Oncogenic mechanisms involving MYB, NFIB , and MYB-NFIB rearrangements have been described, but evidence in the vulva and vagina remains scarce. Our aim is to report the clinicopathologic features, immunohistochemical, and molecular findings in a series of vulvar and vaginal ACCs. Five cases were included. Medical records and slides were reviewed. Formalin-fixed paraffin-embedded material was available in 4 cases, where additional immunohistochemical and molecular studies were carried out. Fluorescence in situ hybridization using MYB, MYBL1 , and NFIB bacterial artificial chromosome-clones break-apart and MYB::NFIB BAC-clones fusion probes was performed. The patients' mean age at diagnosis was 52 years. Tumor size ranged from 0.5 to 5 cm. Microscopic examination revealed tubular, cribriform, and solid patterns. Perineural invasion was seen in 4 cases. Patients were treated with surgery, some with adjuvant radiation therapy. During follow-up (mean: 11 yr), 4 patients developed local recurrences. Recently, one of these patients developed pulmonary disease. Cam 5.2, CK5/6, CD117, and DOG-1 were positive in all 4 cases and S100 and calponin were positive in 3 cases. MYB rearrangement was present in 3 cases, including one with concurrent MYB amplification. There were no MYBL1 or NFIB rearrangements and no MYB :: NFIB fusions. Our findings corroborate that the histologic, immunohistochemical, and oncogenic background is similar between ACCs of the lower female genital tract and ACCs elsewhere, although the canonical MYB::NFIB fusion seems to be a less common finding in this location.

Solid-Basaloid Adenoid Cystic Carcinoma of the Breast: An Aggressive Subtype Enriched for Notch Pathway and Chromatin Modifier Mutations With MYB Overexpression

Adenoid cystic carcinoma (AdCC) is a rare triple-negative breast cancer analogous to its extramammary counterparts. Diagnosis of the more aggressive solid-basaloid variant of AdCC (SB-AdCC) can be challenging due to poorly defined histopathologic and molecular features. We characterized 22 invasive and in situ basaloid carcinomas by morphology, immunohistochemistry, genetics, and MYB status using multiple platforms and assessed clinical behavior and neoadjuvant chemotherapy responses. After consensus review, 16/22 cases were classified as SB-AdCC. All SB-AdCC had predominantly solid growth and at least focal myxohyaline stroma and were immune-poor. Eosinophilic squamoid cells (69%, 11/16) and basement membrane-like secretions (69%, 11/16) were common, and intercalated ducts (31%, 5/16) were less frequent. SB-AdCC typically expressed SOX10 (100%, 16/16) and luminal markers (100%, 16/16 CK7; 88%, 14/16 CD117; 93%, 13/14 CAM5.2). SMA (40%, 6/15) expression was less common, and SMM (27%, 3/11), GATA3 (20%, 3/15), and p63 (25%, 4/16) were mostly negative. MYB protein and/or MYB RNA overexpression was universal in evaluable cases (13/13), with RNA in situ hybridization (10/10) more reliable than immunohistochemistry (10/11, plus 4 excisions inconclusive). Fluorescence in situ hybridization and/or next-generation sequencing identified MYB rearrangements (20%, 3/15) and amplifications/copy gains (60%, 9/15) but no MYB::NFIB fusions. SB-AdCC often had aberrations in Notch pathway (60%, including 40% NOTCH1 and 20% NOTCH2) and/or chromatin modifier (60%, including 33% CREBBP) genes, with relatively infrequent TP53 mutations (27%). Unclassified invasive basaloid carcinomas lacking described histologic features of SB-AdCC (n = 4) and basaloid ductal carcinoma in situ (n = 2) showed similar immunoprofiles and genetics as SB-AdCC, including Notch aberrations and MYB overexpression with MYB rearrangements/amplifications. Overall, nodal (22%) and distant (33%) metastases were common, and 23% of patients died of disease (mean follow-up, 35 months; n = 22). Responses were poor in all 7 neoadjuvant chemotherapy–treated patients, without any achieving pathologic complete response. The data highlight the histopathologic spectrum of basaloid carcinomas including SB-AdCC and reveal shared genetics and MYB activation, which can be diagnostically useful. Aggressive behavior and poor treatment responses emphasize a need for additional treatment approaches.

BPDCN MYB Fusions Bind Cell Cycle Gene Promoters, Reactivate Self-Renewal in Progenitor Cells and Induce Myeloid/Dendritic Leukemia

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare acute leukemia with poor prognosis arising from the plasmacytoid dendritic cell (pDC) lineage. MYB is a hematopoietic transcription factor overexpressed in many leukemias. Genomic rearrangements of MYB were identified in a significant fraction of BPDCNs, including in cases without any other clear driver mutations, and result in its fusion to one of several partner genes (Suzuki et al., Leukemia 2017). These fusions are rare or absent in other acute leukemias and the mechanisms by which they contribute to BPDCN oncogenesis are not understood. To examine the impact of Myb fusions on hematopoietic differentiation and leukemogenesis, we used mouse bone marrow progenitors immortalized by estradiol (E2)-dependent activation of HoxB8 and culture with Flt3 ligand (HoxB8-FL cells). We used HoxB8-FL cells deficient in Cdkn2a, since CDKN2A deletion is present in up to ~67% of BPDCNs (Lucioni et al., Blood 2011) but is rare in other myeloid leukemias. HoxB8-FL cells differentiate into myeloid, lymphoid and dendritic cells in vitro upon withdrawal of E2, or in vivo upon transplantation. They therefore represent lymphoid-primed multipotent progenitor (LMPP)-like cells that are unable to self-renew in the absence of E2. We co-expressed a dTom reporter with V5-tagged Myb constructs in HoxB8-FL cells: wild-type full-length Myb (Myb-FL), truncated Myb (Myb-TR) or Myb-PLEKHO1. MYB-PLEKHO1 is the most frequent fusion in BPDCN patients, while truncated Myb is analogous to recurrent BPDCN MYB fusions in which the partner is out-of-frame. Empty vector was used as a control. HoxB8-FL cells expressing Myb-FL, Myb-TR or Myb-PLEKHO1 displayed arrested differentiation upon withdrawal of E2 in vitro (Figure 1). While all empty vector-transduced cells had upregulated CD11b and/or CD11c at day 7 post-E2 withdrawal, Myb overexpression caused an accumulation of CD11b-CD11c- undifferentiated cells. In vivo, a similar effect was observed at day 7 post-transplantation: dTom+ CD11b-CD11c-CD19-B220- undifferentiated cells were still present in the bone marrow of Myb-FL, Myb-TR and Myb-PLEKHO1 recipient mice, while in empty vector recipients all dTom+ cells expressed at least one of these differentiation markers. Surprisingly, we observed long-term persistence of dTom+ cells in the peripheral blood of Myb-TR and Myb-PLEKHO1, but not Myb-FL, recipients. This developed into lethal malignancy in 100% of Myb-TR and Myb-PLEKHO1 recipients by 28 weeks (Figure 2). Malignant cells showed blast-like morphology of acute leukemia and expressed markers of a myeloid/dendritic progenitor (Kit+CD11b+Cx3cr1+). dTom+ disease was never observed in Myb-FL or empty vector recipients (log-rank P<0.001). Together, while expression of either full-length Myb or Myb fusions impaired myeloid/dendritic differentiation, only Myb rearrangements associated with BPDCN generated a fully penetrant leukemia. To investigate chromatin-level differences between physiologically expressed wild-type MYB and MYB fusions, we performed Cut&Run in K562 cells with V5-tagged MYB-FL, MYB-TR or MYB-PLEKHO1 knocked in to the endogenous MYB locus using CRISPR/Cas9 and homology-directed repair. We observed increased binding of MYB-TR and MYB-PLEKHO1 relative to MYB-FL at promoters of cell cycle genes that function at the G2/M checkpoint, including CDC20, CDCA3 and CKS2. These binding sites contained canonical MYB binding motifs, indicating that MYB fusions increase direct DNA binding at chromatin involved in control of specific cell cycle genes. Cut&Run for V5-Myb-PLEKHO1 in mouse leukemias revealed similar direct DNA binding at cell cycle gene promoters. Moreover, expression of G2/M cell cycle genes was enriched in patient BPDCNs relative to normal pDCs. Our data suggest that BPDCN MYB fusions exert distinct oncogenic effects to overexpression of wild-type MYB. In addition to arresting differentiation, BPDCN MYB fusions can reactivate self-renewal in progenitor cells, which may occur through increased direct DNA binding at cell cycle gene promoters. This may explain the simple genetics of MYB-rearranged BPDCN, which lack other recurrent myeloid-type mutations, if the fusions are sufficient to generate leukemia via these dual roles. These data also indicate that therapeutic strategies targeting MYB and/or specific cell cycle checkpoints may be active in BPDCN. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Adenoid cystic carcinoma of the orbit: a single institute experience

Abstract Introduction/Objective Adenoid cystic carcinoma (ADCC) is a malignant neoplasm usually arising from the major and minor salivary glands. Orbital ADCC arising from the lacrimal gland is rare. They present with morphology and immunohistochemical properties identical to their salivary gland counterparts. Due to their rarity, orbital ADCCs are poorly studied. Here, we describe our institutional experience of diagnosing ADCC in orbit. Methods/Case Report We queried the electronic laboratory information system for primary tumors arising in the orbit that resulted in the diagnosis of ADCC in the last twenty years. Clinical history, radiology, and immunohistochemical profile were obtained and summarized for all cases. Results (if a Case Study enter NA) Eight cases were with the diagnosis of orbital ADCC. The age at diagnosis ranged between 38 to 79 years, with most patients diagnosed between 41 to 50 years. The male to female ratio was 1:1. The tumor size varied between 1.5 to 8.7 cm. Most tumors were graded as grade III and showed perineural invasion. Five out of eight tumors showed predominantly solid architecture. The immunohistochemical pattern was similar to salivary gland ADCC, with one case showing MYB rearrangement. Conclusion Our data suggest that orbital ADCC closely resembles their salivary gland counterparts. Although small, our study broadens the general understanding of this rare group of malignancies.

Development and characterization of patient-derived salivary gland cancer organoid cultures

ObjectiveThree-dimensional organoid cell cultures have been established for a variety of human cancers. For most rare cancers, including salivary gland cancer (SGC), these models are lacking, despite the great unmet need to study cancer biology in these diseases. Therefore, we aimed to develop patient-derived organoid (PDO) models for different subtypes of SGC. MethodsTumor samples of SGC patients were processed and embedded in Matrigel. Successful PDOs (expandable > 1*106 cells) were phenotypically characterized using immunohistochemistry (IHC) and genotypically by gene fusion analysis and by targeted and whole-exome sequencing. Successfully established PDOs were subjected to small-scale drug screening. ResultsOut of 37 attempts, 7 viable short-term PDOs were established (19 % success rate; 3 salivary duct carcinoma, 3 adenoid cystic carcinoma and 1 mucoepidermoid carcinoma). Each PDO showed close phenotypical mimicry to parental tissue. Genotypic characterization revealed that in each PDO > 97.6 % of all COSMIC annotated variants and all MYB, MYBL1 and NFIB gene rearrangements were retained. Drug screening was proven feasible in all PDOs. ConclusionWe present the first comprehensively characterized short-term SGC PDO models for three subtypes of SGC with close phenotypic and genotypic resemblance to parental tissue, which can be used for drug screening applications.

Adenoid cystic carcinoma in children and young adults: Aclinicopathological study of 12 cases.

To investigate the clinicopathological characteristics, immunoprofile, and molecular alterations of adenoid cystic carcinoma (ACC) in children and young adults. Twelve cases of ACC were included. MYB, MYBL1, Ki-67, type IV Collagen, Laminin, and LAMB1 expression were detected by immunohistochemistry. MYB and MYBL1 rearrangements were detected by fluorescence in situ hybridization. Among 12 patients, four were female and eight were male. Seven cases (58.3%) located in major salivary glands and eight cases (66.7%) were classified as Grade I. Ten tumors (83.3%) had collagenous and hyalinized stroma. MYB was positive in 83.3% cases, and the average Ki-67 labeling index (LI) was 8.3%. LAMB1, type IV Collagen, and Laminin were positive in 91.7%, 66.7%, and 58.3% cases, respectively. Besides, three out of eight tumors had MYB rearrangement. Cases without MYB rearrangement were negative for MYBL1 expression and MYBL1 rearrangement. The average follow-up time was 91.8 months. Four patients had recurrent diseases. ACC in children and young adults was seen more frequently in males and major salivary glands. Most cases had ECM and hyaline stroma. Grade III tumors, higher Ki-67 LI, negative expression of type IV Collagen, and Laminin showed a tendency of higher recurrence rate.

TBIO-10. NGS molecular profile of paediatric brain tumours: results from 92 consecutive patients treated at Centro Hospitalar Universitário de São João

Abstract AIM: Our aim was to progress in bringing molecular medicine to routine clinical practice in the setting of paediatric neuro-oncology. We have implemented a protocol between Ipatimup and Centro Hospitalar Universitário de São João for the rapid and efficient delivery of the molecular portrait of paediatric brain tumours. MATERIAL AND METHODS: We have enrolled 92 patients with the following inclusion criteria: Age 0-18 years; newly diagnosed brain tumour; previously diagnosed brain tumour, whenever it presented as rare, aggressive or refractory disease; availability of tumour material; signed informed consent. Tumour samples were centrally reviewed by expert pathologists and profiled using the Oncomine Childhood Cancer Research Assay. RESULTS: In the 92 tumours that were molecularly profiled, BRAF was the most frequently altered gene, especially in pilocytic astrocytomas, being also detected in other LGG and HGG. Other commonly mutated genes were PIK3CA and FGFR, the former in HGG and the latter in LGG. MYB and RAF1 rearrangements were also found in low grade glial/glioneuronal tumours, while HGG showed a more complex profile, with many cases harbouring multiple alterations in EGFR, PDGFRA, ATRX, H3F3A, HIST1H3B, TP53, among others. A 16-year old patient with CMMR (homozygous mutation in PMS2) developed a glioblastoma that carried nearly 5x the average number of mutations. Among the 8 medulloblastomas, 2 showed mutations in the SHH pathway (1 in PTCH1 and one in SUFU) and 2 in the WNT pathway (1 in CTNNB1 and one in APC). In the remaining cases, one ependymoma presented MYCN amplification, while no alterations were detected in 3 patients. CONCLUSIONS: This study enabled the detailed molecular study of 92 paediatric brain patients, allowing a more robust tumour classification and the identification of actionable alterations. A subset of the patients are already undergoing targeted therapy, mainly using BRAF or MEK inhibitors with generally good improvement.

Distinct clinicopathological and genomic features in solid and basaloid adenoid cystic carcinoma of the breast

Adenoid cystic carcinoma (AdCC) of the breast is a rare indolent carcinoma of salivary gland-type tumors, frequently associated with MYB genetic alteration. Solid and basaloid adenoid cystic carcinoma (SB-AdCC) is considered a sparse variant of AdCC. This study sought to search for clinicopathological and genomic features in SB-AdCC. Registered clinicopathological data on a cohort of 13 AdCC of the breast cases, including six conventional adenoid cystic carcinoma (C-AdCC) cases and seven SB-AdCC cases, were collected. MYB gene rearrangement via fluorescent in situ hybridization was investigated and MYB protein expression was evaluated by immunohistochemistry. Compared with C-AdCC, we found that the distribution of SB-AdCC cases were shifted to older age and were more frequently distant metastasis. Moreover, metastasis cases also showed a high (exceed 30%) Ki-67 index. Both groups showed MYB rearrangements and MYB protein expression, but they were less frequent in SB-AdCC than C-AdCC. To conclude, our results suggest that SB-AdCC is an aggressive variant of mammary AdCC with a higher incidence of distant metastases compared with C-AdCC, though they share common molecular features. A high Ki-67 index may be an adverse prognostic factor for metastasis.

The clinical behavior and genomic features of the so-called adenoid cystic carcinomas of the solid variant with basaloid features

Classic adenoid cystic carcinomas (C-AdCCs) of the breast are rare, relatively indolent forms of triple negative cancers, characterized by recurrent MYB or MYBL1 genetic alterations. Solid and basaloid adenoid cystic carcinoma (SB-AdCC) is considered a rare variant of AdCC yet to be fully characterized. Here, we sought to determine the clinical behavior and repertoire of genetic alterations of SB-AdCCs. Clinicopathologic data were collected on a cohort of 104 breast AdCCs (75 C-AdCCs and 29 SB-AdCCs). MYB expression was assessed by immunohistochemistry and MYB-NFIB and MYBL1 gene rearrangements were investigated by fluorescent in-situ hybridization. AdCCs lacking MYB/MYBL1 rearrangements were subjected to RNA-sequencing. Targeted sequencing data were available for 9 cases. The invasive disease-free survival (IDFS) and overall survival (OS) were assessed in C-AdCC and SB-AdCC. SB-AdCCs have higher histologic grade, and more frequent nodal and distant metastases than C-AdCCs. MYB/MYBL1 rearrangements were significantly less frequent in SB-AdCC than C-AdCC (3/14, 21% vs 17/20, 85% P < 0.05), despite the frequent MYB expression (9/14, 64%). In SB-AdCCs lacking MYB rearrangements, CREBBP, KMT2C, and NOTCH1 alterations were observed in 2 of 4 cases. SB-AdCCs displayed a shorter IDFS than C-AdCCs (46.5 vs 151.8 months, respectively, P < 0.001), independent of stage. In summary, SB-AdCCs are a molecularly heterogeneous but clinically aggressive group of tumors. Less than 25% of SB-AdCCs display the genomic features of C-AdCC. Defining whether these tumors represent a single entity or a collection of different cancer types with a similar basaloid histologic appearance is warranted.

Mutational landscape of primary pulmonary salivary gland-type tumors through targeted next-generation sequencing

ObjectivesPrimary pulmonary salivary gland-type tumors (PSGTs) mainly comprise of mucoepidermoid carcinoma (MEC) and adenoid cystic carcinoma (ACC), which are rare and molecularly poorly understood. This study aimed to profile the molecular alterations of PSGTs via targeted next-generation sequencing (NGS). Material and methodsImmunohistochemistry was used to screen PSGTs in 32 patients and MAML2 and MYB rearrangements were detected using fluorescence in situ hybridization. 1021-Genepanel of targeted NGS was conducted to profile genomic mutations in all the PSGT patients. ResultsAmong the 32 patients, 25 had MEC and 7 had ACC. MAML2 and MYB rearrangements were detected in 80.0% (20/25) of the MEC and 71.4% (5/7) of the ACC patients. Among the MEC patients, 10 (40.0%) had ≥1 mutation, and 6 of them had 11 isolated mutations with abundance >5%, namely NFE2L2, MYOD1, INPP4B, CCND2, SNTG1, HSPD1, TGFBR1, RBM10, NOTCH4, ASXL1, and PTPRD mutations. The remaining 4 patients had 9 mutations with abundance <5%, namely KMT2A, PDCD11, FLT1, BRCA2, APC, SLX4, FOXP1, FGFR1, and HRAS mutations. All the ACC patients had mutations, which were enriched in 5 pathways including the PI3K and NOTCH pathways, chromatin and cytoskeleton remodeling, and DNA damage. These results explain PSGTs harbor distinct driver features of MAML2 or MYB rearrangement, accompanied with wide mutational diversity with very low rate of somatic mutation. Several important pathways, including the NOTCH and PI3K pathways, and chromatin remodeling could be targeted to improve the survival in patients with ACC.

Recent updates in salivary gland tumors of the lung.

Salivary gland tumors are uncommon primary lesions in the lung. Their morphologic, immunophenotypic, and molecular characteristics resemble those of their counterparts in the head and neck or elsewhere. Most common primary pulmonary salivary gland tumors include mucoepidermoid carcinoma, adenoid cystic carcinoma, and epithelial-myoepithelial carcinoma. The study of these neoplasms is hampered by their paucity. Therefore, studies are in general small or restricted to individual cases. Despite this challenge recent advances have been made specifically at the molecular level. Molecular alterations such as MAML2 rearrangements in mucoepidermoid carcinoma, MYB rearrangements in adenoid cystic carcinomas, and EWSR1 rearrangements in hyalinizing clear cell carcinomas and myoepithelial tumors have been identified. These molecular alterations might be helpful in the distinction of these salivary gland tumors from other neoplasms in the lung. However, the distinction from metastatic disease remains challenging. Awareness of these tumors and knowledge of available ancillary studies to confirm the diagnosis is important to avoid misdiagnosis which might lead to differences in treatment, management, and prognosis. Further studies are needed to identify biomarkers to better predict patient's outcome and for individual management and treatment of patients.

MYB rearrangements and over-expression in T-cell acute lymphoblastic leukemia.

We investigated MYB rearrangements (MYB-R) and the levels of MYB expression, in 331 pediatric and adult patients with T-cell acute lymphoblastic leukemia (T-ALL). MYB-R were detected in 17 cases and consisted of MYB tandem duplication (tdup) (= 14) or T cell receptor beta locus (TRB)-MYB (= 3). As previously reported, TRB-MYB was found only in children (1.6%) while MYB tdup occurred in both age groups, although it was slightly more frequent in children (5.2% vs 2.8%). Shared features of MYB-R T-ALL were a non-early T-cell precursor (ETP) phenotype, a high incidence of NOTCH1/FBXW7 mutations (81%) and CDKN2AB deletions (70.5%). Moreover, they mainly belonged to HOXA (=8), NKX2-1/2-2/TLX1 (=4), and TLX3 (=3) homeobox-related subgroups. Overall, MYB-R cases had significantly higher levels of MYB expression than MYB wild type (MYB-wt) cases, although high levels of MYB were detected in ~ 30% of MYB-wt T-ALL. Consistent with the transcriptional regulatory networks, cases with high MYB expression were significantly enriched within the TAL/LMO subgroup (P = .017). Interestingly, analysis of paired diagnosis/remission samples demonstrated that a high MYB expression was restricted to the leukemic clone. Our study has indicated that different mechanisms underlie MYB deregulation in 30%-40% of T-ALL and highlighted that, MYB has potential as predictive/prognostic marker and/or target for tailored therapy.

Primary Pituitary Adenoid Cystic Carcinoma: A Rare Salivary Gland-Like Tumor in the Sella.

Adenoid cystic carcinoma (ACC) is a tumor of the exocrine glands that originates primarily from the minor and major salivary glands, nasopharynx, and lacrimal glands. ACC grows slowly but is locally aggressive and prone to recurrence. It is uncommon for ACCs to develop in the pituitary gland as a primary tumor. We present a case of primary pituitary ACC extending to the sphenoid sinus resembling an invasive adenoma in a 71-year-old woman with a history of nasal epistaxis. We reviewed other reported cases of pituitary ACCs with retrospective validation of whether the tumor was primary or not. The intrasellar tumor exhibited MYB rearrangement with enlargement and destruction of the sella turcica and dural tears toward the sphenoid sinus, which would be consistent for a tumor originating from the pituitary gland. Including our case, only four intrasellar and one suprasellar ACC have been confirmed as primary tumors. All intrasellar ACCs had the characteristic of some form of invasion of neighboring structures with evidence of hyperprolactinemia. ACC could develop in the pituitary gland as a form of salivary gland-like tumor derived from the ectopic salivary gland rests. ACCs rarely arise from the pituitary gland; however, the accurate determination of primary occurrence is difficult because of the invasive nature of these tumors, and the anatomical relationship with the sphenoid sinus and the cavernous sinus. Excessive bleeding from the tumor or unexpected internal carotid artery injury should be avoided during surgery for primary and secondary pituitary ACC.

Adenoid cystic carcinoma and basaloid carcinoma of the breast: A clinicopathological study

Adenoid cystic carcinoma of the breast (ACCB) is a rare triple negative tumor (TNT) with an excellent prognosis in most cases. Three different histologic types are recognized: classic ACCB, solid basaloid ACCB (SB-ACCB), and ACCB with high-grade transformation. A majority of these tumors show characteristic molecular and immunohistochemical (IHC) features, with fusion of MYB and NFIB genes and overexpression of MYB, respectively. Basaloid carcinomas of the breast (BCB) are infrequently described. They resemble SB-ACCB and TNT of no special type (TNT-NST).We have studied the clinicopathological features of 17 ACCB and 9 BCB, investigating the expression of MYB by IHC and the rearrangements of MYB by fluorescence in situ hybridization (FISH).MYB was expressed by IHC in 15 ACCB and in 3 BCB. MYB FISH detected rearrangements in 11 ACCB and in 2 BCB.After a mean follow-up of 90 months, with a range of 12–204 months, 2 patients with ACCB with high-grade transformation and 1 patient with BCB developed metastases and died of disease.In summary, most ACCB have a good prognosis, but tumors with adverse histopathological features may metastasize. BCB may overlap with ACCB and TNT-NST, and their prognosis should be further studied.

LGG-31. CHARACTERIZING TEMPORAL GENOMIC HETEROGENEITY IN PEDIATRIC LOW GRADE GLIOMAS: ANALYSIS OF AN EXPANDED MULTI-INSTITUTIONAL COHORT WITH 101 PAIRED TUMOR SAMPLES

INTRODUCTIONRecent discoveries have provided valuable insight into the genomic landscape of pediatric low grade gliomas (LGGs) at diagnosis, facilitating molecularly targeted treatment. However, little is known about their temporal and therapy-related genomic heterogeneity. An adequate understanding of the evolution of pediatric LGGs’ genomic profiles over time is critically important in guiding decisions about targeted therapeutics and diagnostic biopsy at recurrence.METHODSFluorescence in situ hybridization, mutation-specific immunohistochemistry, and exome analyses were performed on paired tumor samples from primary diagnostic and subsequent surgeries.RESULTS101 tumor samples from 48 patients (43 with 2 specimens, 5 with 3 specimens) from 3 institutions underwent testing. BRAF fusion and BRAFV600E status were conserved in 100% and 97% of paired specimens, respectively. No loss or gain of IDH1 mutations or FGFR1, NTRK2, MYB, or MYBL1 rearrangements were detected over time. Histologic diagnosis remained the same in all tumors, with no acquired H3K27M mutations or malignant transformation. CDKN2A deletions were acquired in 7 patients (including 3 who received chemotherapy [2 with temozolomide] and 1 who received radiation), and were associated with a trend toward shorter time to progression (median: 5.5 vs. 13.0 months [p=0.08]).CONCLUSIONSMost targetable genetic alterations in pediatric LGGs, including BRAF alterations, are conserved at recurrence and following chemotherapy or radiation. However, CDKN2A deletion acquisition was demonstrated and may define a higher risk group. Given potential for targeted therapies for tumors acquiring CDKN2A deletions, performing a biopsy at recurrence may be indicated in certain patients, especially those with rapid progression.

MYB RNA In Situ Hybridization Facilitates Sensitive and Specific Diagnosis of Adenoid Cystic Carcinoma Regardless of Translocation Status

Adenoid cystic carcinoma (AdCC) can demonstrate histologic and immunohistochemical (IHC) overlap with a wide range of salivary and nonsalivary tumors, especially in small biopsy specimens. While MYB fluorescence in situ hybridization (FISH) frequently is used to confirm the diagnosis of AdCC, the pathognomonic MYB-NFIB fusion is only present in 40% to 70% of cases. Likewise, although MYB RNA overexpression is seen in the vast majority of AdCC regardless of translocation status, MYB IHC has shown suboptimal specificity for this diagnosis. In this study, we sought to determine whether a novel chromogenic RNA in situ hybridization (ISH) platform could directly detect MYB RNA overexpression and offer a rapid diagnostic adjunct for AdCC. We performed MYB RNA ISH on 84 cases of AdCC as well as 128 other salivary tumors and 108 basaloid and sinonasal carcinomas that mimic AdCC. MYB RNA ISH was 92% sensitive for AdCC, including 97% of cases with MYB rearrangement and 83% without MYB rearrangement by FISH. It was also 89% specific for AdCC overall, with 95% specificity among other salivary tumors and 81% specificity in basaloid and sinonasal carcinomas. In contrast, MYB IHC was 94% sensitive but just 54% specific for AdCC. Overall, MYB RNA ISH provides superior sensitivity for the diagnosis of AdCC compared with MYB FISH and superior specificity compared with MYB IHC. This assay could provide a useful tool for rapidly confirming the diagnosis of AdCC in formalin-fixed, paraffin-embedded specimens.

P16 Immunoexpression in sinonasal and nasopharyngeal adenoid cystic carcinomas: a potential pitfall in ruling out HPV‐related multiphenotypic sinonasal carcinoma

Adenoid cystic carcinoma (AdCC) is frequent in the sinonasal region. The recently described human papilloma virus (HPV)-related multiphenotypic sinonasal carcinoma (HMSC) histopathologically resembles solid AdCC, but has a better outcome. Thus, clinical and pathogenetic differences between HMSC and sinonasal AdCC necessitate their distinction. We conducted this study to assess p16 immunoexpression in previously diagnosed AdCC cases, and to identify HMSC cases in p16 immunopositive cases. Cases diagnosed as sinonasal and nasopharyngeal AdCC were retrieved. Histomorphological features were reviewed. Immunohistochemistry (IHC) for p16 was performed. HPV testing was performed in p16-positive cases by mRNA in-situ hybridisation (mRNA ISH) and polymerase chain reaction (PCR) assay. MYB rearrangement was assessed by fluorescence in-situ hybridisation. One hundred and two AdCC cases were retrieved. Six cases (5.9%) showed diffuse p16 positivity. HPV mRNA ISH and PCR were negative in p16-positive cases. Two cases showed MYB rearrangement. p16-positive cases were composed of basaloid cells demonstrating a cribriform pattern, at least focally. The predominant pattern was cribriform in three and solid in three cases. One case showed two distinct components: keratinising squamous cell carcinoma and cribriform AdCC. Other morphological patterns seen were tubular, reticular, epithelial-myoepithelial carcinoma-like, and glomeruloid, forming a minor component of the tumour area. p16 staining alone, even when diffuse and strong, cannot be used as a surrogate for HPV testing to distinguish sinonasal AdCC from HMSC. p16 IHC should be accompanied by more specific methods, such as mRNA ISH, so as not to erroneously diagnose HMSC over sinonasal AdCC, bearing in mind the highly aggressive nature of the latter.

Gliome de bas grade avec altération de MYBL1 : observation d’une nouvelle entité tumorale pédiatrique

Diffuse gliomas with MYB or MYBL1 alterations are rare tumours mostly affecting children or young adults with long-term epilepsy. This category of glioma includes two morphological subtypes. The angiocentric subtype is characterized by an angiocentric pattern of growth and a frequent MYB:QKI fusion. The isomorphic subtype corresponds to a highly differentiated astrocytic glioma with low cellularity, low proliferation and no specific microscopic features. The diagnosis is based on the imaging, demonstrating a supratentorial tumor, associated with the confirmation of a MYB or MYBL1 rearrangement. Here, we report the case of a 7-year-old child who presented a right frontal brain lesion corresponding to an isomorphic diffuse glioma with MYBL1 alteration.

Solid-type adenoid cystic carcinoma of the breast, a distinct molecular entity enriched in NOTCH and CREBBP mutations.

Adenoid cystic carcinoma (ACC) of the breast with a predominant solid pattern is difficult to diagnose with certainty and differentiate from more common triple-negative breast cancers (TNBCs) of basal-phenotype. To better characterize solid ACC, we performed a clinical, morphological, immunohistochemical, and molecular comparative analysis of 33 ACCs of the breast comprising 17 solid variant ACCs and 16 conventional ACCs. Solid ACCs displayed basaloid morphology with an exclusive or predominant epithelial cell population associated with decreased myoepithelial differentiation, while demonstrating MYB protein overexpression similar to the more common type of ACC. Strong and diffuse MYB expression by immunochemistry was observed in 14/17 (82%) of solid ACCs while MYB rearrangements were detected by break apart fluorescence in situ hybridization (FISH) in only 3/16 (19%) of solid ACCs. Conversely, weak MYB immunohistochemical expression was observed in only 7/204 (3%) of TNBC. Solid ACCs displayed a transcriptomic profile distinct from conventional ACCs with 549 genes showing a highly significant differential expression between conventional and solid ACC [false discovery rate (FDR) < 0.01; log2FC > |1|]. EnrichR and Kegg Pathway analyses identified PI3K-Akt and focal adhesion signaling pathways as significantly overexpressed in conventional ACCs compared with solid ACCs which significantly overexpressed the nitrogen metabolism pathway. CREBBP mutations and NOTCH activating gene mutations were only present in solid ACCs, concerning 5/16 (31%) of cases for each gene. Tumors with NOTCH activating mutations displayed a strong diffuse nuclear NICD1 staining, an established marker of Notch pathway activation. Solid ACCs also differed from basal-type TNBC, with fewer TP53 mutations and a more stable genomic profile on array comparative genomic hybridization (CGH). In summary, solid-type ACC of the breast is a distinct molecular entity within the ACC family and is different from common basal-type TNBC. MYB is a diagnostically useful biomarker of solid ACC and NOTCH could be a novel potential therapeutic target in 30% of cases.