Therapy-Induced Senescence Contributes to the Efficacy of Abemaciclib in Patients with Dedifferentiated Liposarcoma.

PURPOSE: We conducted research on CDK4/6 inhibitors (CDK4/6i) simultaneously in the preclinical and clinical spaces to gain a deeper understanding of how senescence influences tumor growth in humans. PATIENTS AND METHODS: We coordinated a first-in-kind phase II clinical trial of the CDK4/6i abemaciclib for patients with progressive dedifferentiated liposarcoma (DDLS) with cellular studies interrogating the molecular basis of geroconversion. RESULTS: Thirty patients with progressing DDLS enrolled and were treated with 200 mg of abemaciclib twice daily. The median progression-free survival was 33 weeks at the time of the data lock, with 23 of 30 progression-free at 12 weeks (76.7%, two-sided 95% CI, 57.7%-90.1%). No new safety signals were identified. Concurrent preclinical work in liposarcoma cell lines identified ANGPTL4 as a necessary late regulator of geroconversion, the pathway from reversible cell-cycle exit to a stably arrested inflammation-provoking senescent cell. Using this insight, we were able to identify patients in which abemaciclib induced tumor cell senescence. Senescence correlated with increased leukocyte infiltration, primarily CD4-positive cells, within a month of therapy. However, those individuals with both senescence and increased TILs were also more likely to acquire resistance later in therapy. These suggest that combining senolytics with abemaciclib in a subset of patients may improve the duration of response. CONCLUSIONS: Abemaciclib was well tolerated and showed promising activity in DDLS. The discovery of ANGPTL4 as a late regulator of geroconversion helped to define how CDK4/6i-induced cellular senescence modulates the immune tumor microenvironment and contributes to both positive and negative clinical outcomes. See related commentary by Weiss et al., p. 649.

Clinical sequencing of soft tissue and bone sarcomas delineates diverse genomic landscapes and potential therapeutic targets.

The genetic, biologic, and clinical heterogeneity of sarcomas poses a challenge for the identification of therapeutic targets, clinical research, and advancing patient care. Because there are > 100 sarcoma subtypes, in-depth genetic studies have focused on one or a few subtypes. Herein, we report a comparative genetic analysis of 2,138 sarcomas representing 45 pathological entities. This cohort is prospectively analyzed using targeted sequencing to characterize subtype-specific somatic alterations in targetable pathways, rates of whole genome doubling, mutational signatures, and subtype-agnostic genomic clusters. The most common alterations are in cell cycle control and TP53, receptor tyrosine kinases/PI3K/RAS, and epigenetic regulators. Subtype-specific associations include TERT amplification in intimal sarcoma and SWI/SNF alterations in uterine adenosarcoma. Tumor mutational burden, while low compared to other cancers, varies between and within subtypes. This resource will improve sarcoma models, motivate studies of subtype-specific alterations, and inform investigations of genetic factors and their correlations with treatment response.

Same-Cell Co-Occurrence of RAS Hotspot and BRAF V600E Mutations in Treatment-Naive Colorectal Cancer.

PURPOSE: Mitogen-activated protein kinase pathway-activating mutations occur in the majority of colorectal cancer (CRC) cases and show mutual exclusivity. We identified 47 epidermal growth factor receptor/BRAF inhibitor-naive CRC patients with dual RAS hotspot/BRAF V600E mutations (CRC-DD) from a cohort of 4,561 CRC patients with clinical next-generation sequencing results. We aimed to define the molecular phenotypes of the CRC-DD and to test if the dual RAS hotspot/BRAF V600E mutations coexist within the same cell. MATERIALS AND METHODS: We developed a single-cell genotyping method with a mutation detection rate of 96.3% and a genotype prediction accuracy of 92.1%. Mutations in the CRC-DD cohort were analyzed for clonality, allelic imbalance, copy number, and overall survival. RESULTS: Application of single-cell genotyping to four CRC-DD revealed the co-occurrence of both mutations in the following percentages of cells per case: NRAS G13D/KRAS G12C, 95%; KRAS G12D/NRAS G12V, 48%; BRAF V600E/KRAS G12D, 44%; and KRAS G12D/NRAS G13V, 14%, respectively. Allelic imbalance favoring the oncogenic allele was less frequent in CRC-DD (24 of 76, 31.5%, somatic mutations) compared with a curated cohort of CRC with a single-driver mutation (CRC-SD; 119 of 232 mutations, 51.3%; P = .013). Microsatellite instability-high status was enriched in CRC-DD compared with CRC-SD (23% v 11.4%, P = .028). Of the seven CRC-DD cases with multiregional sequencing, five retained both driver mutations throughout all sequenced tumor sites. Both CRC-DD cases with discordant multiregional sequencing were microsatellite instability-high. CONCLUSION: Our findings indicate that dual-driver mutations occur in a rare subset of CRC, often within the same tumor cells and across multiple tumor sites. Their presence and a lower rate of allelic imbalance may be related to dose-dependent signaling within the mitogen-activated protein kinase pathway.

A High-Content Screen for C/EBPα Expression Identifies Novel Therapeutic Agents in Dedifferentiated Liposarcoma.

PURPOSE: Dedifferentiated liposarcoma (DDLS), one of the most common and aggressive sarcomas, infrequently responds to chemotherapy. DDLS survival and growth depend on underexpression of C/EBPα, a tumor suppressor and transcriptional regulator controlling adipogenesis. We sought to screen and prioritize candidate drugs that increase C/EBPα expression and may therefore serve as differentiation-based therapies for DDLS. EXPERIMENTAL DESIGN: We screened known bioactive compounds for the ability to restore C/EBPα expression and inhibit proliferation selectively in two DDLS cell lines but not in normal adipose-derived stem cells (ASC). Selected hits' activity was validated, and the mechanism of the most potent, SN-38, was investigated. The in vivo efficacy of irinotecan, the prodrug of SN-38, was evaluated in DDLS xenograft models. RESULTS: Of 3,119 compounds, screen criteria were met by 19. Validation experiments confirmed the DDLS selectivity of deguelin, emetine, and SN-38 and showed that they induce apoptosis in DDLS cells. SN-38 had the lowest IC50 (approximately 10 nmol/L), and its pro-apoptotic effects were countered by knockdown of CEBPA but not of TP53. Irinotecan significantly inhibited tumor growth at well-tolerated doses, induced nuclear expression of C/EBPα, and inhibited HIF1α expression in DDLS patient-derived and cancer cell line xenograft models. In contrast, doxorubicin, the most common treatment for nonresectable DDLS, reduced tumor growth by 30% to 50% at a dose that caused weight loss. CONCLUSIONS: This high-content screen revealed potential treatments for DDLS. These include irinotecan, which induces apoptosis of DDLS cells in a C/EBPα-dependent, p53-independent manner, and should be clinically evaluated in patients with advanced DDLS.

Genetic characterisation of adult primary pleomorphic uterine rhabdomyosarcoma and comparison with uterine carcinosarcoma.

AIMS: To characterise the genetic alterations in adult primary uterine rhabdomyosarcomas (uRMSs) and to investigate whether these tumours are genetically distinct from uterine carcinosarcomas (UCSs). METHODS AND RESULTS: Three tumours originally diagnosed as primary adult pleomorphic uRMS were subjected to massively parallel sequencing targeting 468 cancer-related genes and RNA-sequencing. Mutational profiles were compared with those of UCSs (n = 57) obtained from The Cancer Genome Atlas. Sequencing data analyses were performed using validated bioinformatic approaches. Pathogenic TP53 mutations and high levels of genomic instability were detected in the three cases. uRMS1 harboured a likely pathogenic YTHDF2-FOXR1 fusion. uRMS2 harboured a PPP2R1A hotspot mutation and amplification of multiple genes, including WHSC1L1, FGFR1, MDM2, and CCNE1, whereas uRMS3 harboured an FBXW7 hotspot mutation and an ANKRD11 homozygous deletion. Hierarchical clustering of somatic mutations and copy number alterations revealed that these tumours initially diagnosed as pleomorphic uRMSs and UCSs were similar. Subsequent comprehensive pathological re-review of the three uRMSs revealed previously unidentified minute pan-cytokeratin-positive atypical glands in one case (uRMS3), favouring its reclassification as UCS with extensive rhabdomyosarcomatous overgrowth. CONCLUSIONS: Adult pleomorphic uRMSs harbour TP53 mutations and high levels of copy number alterations. Our findings underscore the challenge in discriminating between uRMS and UCS with rhabdomyosarcomatous differentiation.

Pleomorphic adenomas and mucoepidermoid carcinomas of the breast are underpinned by fusion genes.

Primary pleomorphic adenomas (PAs) and mucoepidermoid carcinomas (MECs) of the breast are vanishingly rare. Here we sought to determine whether breast PAs and MECs would be underpinned by the fusion genes reported to occur in their salivary gland counterparts. Our study included three breast PAs and one breast MEC, which were subjected to RNA sequencing (PAs, n = 2; MEC, n = 1) or to Archer FusionPlex sequencing (PA, n = 1). Our analyses revealed the presence of the HMGA2-WIF1 fusion gene in breast PA3, the CTNNB1-PLAG1 fusion gene in breast PA2, and the CRTC1-MAML2 fusion gene in the breast MEC analyzed (1/1). No oncogenic fusion genes were detected in breast PA1, and no additional oncogenic fusion genes were detected in the cases studied. The presence of the fusion genes identified was validated by fluorescence in situ hybridization (n = 1), reverse transcription-PCR (n = 1), or by both methods (n = 1). Taken together, our findings indicate that PAs and MECs arising in the breast resemble their salivary gland counterparts not only phenotypically but also at the genetic level. Furthermore, our data suggest that the molecular analysis of breast PAs and MECs might constitute a useful tool to aid in their differential diagnosis.

Novel insights into breast cancer copy number genetic heterogeneity revealed by single-cell genome sequencing.

Copy number alterations (CNAs) play an important role in molding the genomes of breast cancers and have been shown to be clinically useful for prognostic and therapeutic purposes. However, our knowledge of intra-tumoral genetic heterogeneity of this important class of somatic alterations is limited. Here, using single-cell sequencing, we comprehensively map out the facets of copy number alteration heterogeneity in a cohort of breast cancer tumors. Ou/var/www/html/elife/12-05-2020/backup/r analyses reveal: genetic heterogeneity of non-tumor cells (i.e. stroma) within the tumor mass; the extent to which copy number heterogeneity impacts breast cancer genomes and the importance of both the genomic location and dosage of sub-clonal events; the pervasive nature of genetic heterogeneity of chromosomal amplifications; and the association of copy number heterogeneity with clinical and biological parameters such as polyploidy and estrogen receptor negative status. Our data highlight the power of single-cell genomics in dissecting, in its many forms, intra-tumoral genetic heterogeneity of CNAs, the magnitude with which CNA heterogeneity affects the genomes of breast cancers, and the potential importance of CNA heterogeneity in phenomena such as therapeutic resistance and disease relapse.

Cells in the body remain healthy by tightly preventing and repairing random changes, or mutations, in their genetic material. In cancer cells, however, these mechanisms can break down. When these cells grow and multiply, they can then go on to accumulate many mutations. As a result, cancer cells in the same tumor can each contain a unique combination of genetic changes. This genetic heterogeneity has the potential to affect how cancer responds to treatment, and is increasingly becoming appreciated clinically. For example, if a drug only works against cancer cells carrying a specific mutation, any cells lacking this genetic change will keep growing and cause a relapse. However, it is still difficult to quantify and understand genetic heterogeneity in cancer. Copy number alterations (or CNAs) are a class of mutation where large and small sections of genetic material are gained or lost. This can result in cells that have an abnormal number of copies of the genes in these sections. Here, Baslan et al. set out to explore how CNAs might vary between individual cancer cells within the same tumor. To do so, thousands of individual cancer cells were isolated from human breast tumors, and a technique called single-cell genome sequencing used to screen the genetic information of each of them. These experiments confirmed that CNAs did differ ­ sometimes dramatically ­ between patients and among cells taken from the same tumor. For example, many of the cells carried extra copies of well-known cancer genes important for treatment, but the exact number of copies varied between cells. This heterogeneity existed for individual genes as well as larger stretches of DNA: this was the case, for instance, for an entire section of chromosome 8, a region often affected in breast and other tumors. The work by Baslan et al. captures the sheer extent of genetic heterogeneity in cancer and in doing so, highlights the power of single-cell genome sequencing. In the future, a finer understanding of the genetic changes present at the level of an individual cancer cell may help clinicians to manage the disease more effectively.

Identification of recurrent FHL2-GLI2 oncogenic fusion in sclerosing stromal tumors of the ovary.

Sclerosing stromal tumor (SST) of the ovary is a rare type of sex cord-stromal tumor (SCST), whose genetic underpinning is currently unknown. Here, using whole-exome, targeted capture and RNA-sequencing, we report recurrent FHL2-GLI2 fusion genes in 65% (17/26) of SSTs and other GLI2 rearrangements in additional 15% (4/26) SSTs, none of which are detected in other types of SCSTs (n = 48) or common cancer types (n = 9,950). The FHL2-GLI2 fusions result in transcriptomic activation of the Sonic Hedgehog (SHH) pathway in SSTs. Expression of the FHL2-GLI2 fusion in vitro leads to the acquisition of phenotypic characteristics of SSTs, increased proliferation, migration and colony formation, and SHH pathway activation. Targeted inhibition of the SHH pathway results in reversal of these oncogenic properties, indicating its role in the pathogenesis of SSTs. Our results demonstrate that the FHL2-GLI2 fusion is likely the oncogenic driver of SSTs, defining a genotypic-phenotypic correlation in ovarian neoplasms.

Sclerosing epithelioid mesenchymal neoplasm of the pancreas - a proposed new entity.

We have encountered pancreatic tumors with unique histologic features, which do not conform to any of the known tumors of the pancreas or other anatomical sites. We aimed to define their clinicopathologic features and whether they are characterized by recurrent molecular signatures. Eight cases were identified; studied histologically and by immunohistochemistry. Selected cases were also subjected to whole-exome sequencing (WES; n = 4), RNA-sequencing (n = 6), Archer FusionPlex assay (n = 5), methylation profiling using the Illumina MethylationEPIC (850k) array platform (n = 6), and TERT promoter sequencing (n = 5). Six neoplasms occurred in females. The mean age was 43 years (range: 26-75). Five occurred in the head/neck of the pancreas. All patients were treated surgically; none received neoadjuvant/adjuvant therapy. All patients are free of disease after 53 months of median follow-up (range: 8-94). The tumors were well-circumscribed, and the median size was 1.8 cm (range: 1.3-5.8). Microscopically, the unencapsulated tumors had a geographic pattern of epithelioid cell nests alternating with spindle cell fascicles. Some areas showed dense fibrosis, in which enmeshed tumor cells imparted a slit-like pattern. The predominant epithelioid cells had scant cytoplasm and round-oval nuclei with open chromatin. The spindle cells displayed irregular, hyperchromatic nuclei. Mitoses were rare. No lymph node metastases were identified. All tumors were positive for vimentin, CD99 and cytokeratin (patchy), while negative for markers of solid pseudopapillary neoplasm, neuroendocrine, acinar, myogenic/rhabdoid, vascular, melanocytic, or lymphoid differentiation, gastrointestinal stromal tumor as well as MUC4. Whole-exome sequencing revealed no recurrent somatic mutations or amplifications/homozygous deletions in any known oncogenes or tumor suppressor genes. RNA-sequencing and the Archer FusionPlex assay did not detect any recurrent likely pathogenic gene fusions. Single sample gene set enrichment analysis revealed that these tumors display a likely mesenchymal transcriptomic program. Unsupervised analysis (t-SNE) of their methylation profiles against a set of different mesenchymal neoplasms demonstrated a distinct methylation pattern. Here, we describe pancreatic neoplasms with unique morphologic/immunophenotypic features and a distinct methylation pattern, along with a lack of abnormalities in any of key genetic drivers, supporting that these neoplasms represent a novel entity with an indolent clinical course. Given their mesenchymal transcriptomic features, we propose the designation of "sclerosing epithelioid mesenchymal neoplasm" of the pancreas.

Molecular Characterization of a Rare Dedifferentiated Liposarcoma With Rhabdomyosarcomatous Differentiation in a 24 Year Old.

Aims. The aim of this study was to identify potential driver genetic alterations in a dedifferentiated liposarcoma (DDLPS) with rhabdomyosarcomatous differentiation. Methods and Results. A 24-year-old female underwent resection of an abdominal mass, which on a previous biopsy demonstrated rhabdomyosarcomatous differentiation concerning for embryonal rhabdomyosarcoma. Histologically the resected tumor displayed a high-grade sarcoma with rhabdomyosarcomatous differentiation in the background of well-differentiated liposarcoma consistent with DDLPS. Fluorescence in situ hybridization confirmed MDM2 amplification, as did array-based copy number profiling. Whole-exome sequencing revealed a somatic FGFR1 hotspot mutation and RNA sequencing an LMNB2-MAP2K6 fusion only within the dedifferentiated component. Conclusions. This study represents an in-depth examination of a rare DDLPS with rhabdomyosarcomatous differentiation in a young individual. Additionally, it is also instructive of a potential pitfall when assessing for MDM2 amplification in small biopsies. Despite exhaustive analysis, mutation and gene copy number analysis did not identify any molecular events that would underlie the rhabdomyoblastic differentiation. Our understanding of what causes some tumors to dedifferentiate as well as undergo divergent differentiation is limited, and larger studies are needed.

Erratum: Publisher Correction: Homologous recombination DNA repair defects in PALB2-associated breast cancers.

[This corrects the article DOI: 10.1038/s41523-019-0115-9.].

Homologous recombination DNA repair defects in PALB2-associated breast cancers.

Mono-allelic germline pathogenic variants in the Partner And Localizer of BRCA2 (PALB2) gene predispose to a high-risk of breast cancer development, consistent with the role of PALB2 in homologous recombination (HR) DNA repair. Here, we sought to define the repertoire of somatic genetic alterations in PALB2-associated breast cancers (BCs), and whether PALB2-associated BCs display bi-allelic inactivation of PALB2 and/or genomic features of HR-deficiency (HRD). Twenty-four breast cancer patients with pathogenic PALB2 germline mutations were analyzed by whole-exome sequencing (WES, n = 16) or targeted capture massively parallel sequencing (410 cancer genes, n = 8). Somatic genetic alterations, loss of heterozygosity (LOH) of the PALB2 wild-type allele, large-scale state transitions (LSTs) and mutational signatures were defined. PALB2-associated BCs were found to be heterogeneous at the genetic level, with PIK3CA (29%), PALB2 (21%), TP53 (21%), and NOTCH3 (17%) being the genes most frequently affected by somatic mutations. Bi-allelic PALB2 inactivation was found in 16 of the 24 cases (67%), either through LOH (n = 11) or second somatic mutations (n = 5) of the wild-type allele. High LST scores were found in all 12 PALB2-associated BCs with bi-allelic PALB2 inactivation sequenced by WES, of which eight displayed the HRD-related mutational signature 3. In addition, bi-allelic inactivation of PALB2 was significantly associated with high LST scores. Our findings suggest that the identification of bi-allelic PALB2 inactivation in PALB2-associated BCs is required for the personalization of HR-directed therapies, such as platinum salts and/or PARP inhibitors, as the vast majority of PALB2-associated BCs without PALB2 bi-allelic inactivation lack genomic features of HRD.

PAX8-GLIS3 gene fusion is a pathognomonic genetic alteration of hyalinizing trabecular tumors of the thyroid.

The hyalinizing trabecular adenoma/tumor is a rare and poorly characterized follicular-derived thyroid neoplasm recently shown to harbor recurrent PAX8-GLIS1 or PAX8-GLIS3 gene fusions. Here we sought to define the repertoire of genetic alterations of hyalinizing trabecular tumors, and whether PAX8-GLIS3 fusions are pathognomonic for hyalinizing trabecular tumors. A discovery series of eight hyalinizing trabecular tumors was subjected to RNA-sequencing (n = 8), whole-exome sequencing (n = 3) or targeted massively parallel sequencing (n = 5). No recurrent somatic mutations or copy number alterations were identified in hyalinizing trabecular tumor, whereas RNA-sequencing revealed the presence of a recurrent genetic rearrangement involving PAX8 (2q14.1) and GLIS3 (9p24.2) genes in all cases. In this in-frame fusion gene, which comprised exons 1-2 of PAX8 and exons 3-11 of GLIS3, GLIS3 is likely placed under the regulation of PAX8. Reverse transcription RT-PCR and/or fluorescence in situ hybridization analyses of a validation series of 26 hyalinizing trabecular tumors revealed that the PAX8-GLIS3 gene fusion was present in all hyalinizing trabecular tumors (100%). No GLIS1 rearrangements were identified. Conversely, no PAX8-GLIS3 gene fusions were detected in a cohort of 237 control thyroid neoplasms, including 15 trabecular thyroid lesions highly resembling hyalinizing trabecular tumor from a morphological standpoint, as well as trabecular/solid follicular adenomas, solid/trabecular variants of papillary carcinoma, and Hurthle cell adenomas or carcinomas. Our data provide evidence to suggest that the PAX8-GLIS3 fusion is pathognomonic for hyalinizing trabecular tumors, and that the presence of the PAX8-GLIS3 fusion in thyroid neoplasms may be used as an ancillary marker for the diagnosis of hyalinizing trabecular tumor, thereby avoiding overtreatment in case of misdiagnoses with apparently similar malignant tumors.

Whole-exome sequencing and RNA sequencing analyses of acinic cell carcinomas of the breast.

AIMS: Acinic cell carcinoma (ACC) of the breast is a rare histological form of triple-negative breast cancer (TNBC). Despite its unique histology, targeted sequencing analysis has failed to identify recurrent genetic alterations other than those found in common forms of TNBC. Here we subjected three breast ACCs to whole-exome and RNA sequencing to determine whether they would harbour a pathognomonic genetic alteration. METHODS AND RESULTS: DNA and RNA samples from three breast ACCs were subjected to whole-exome sequencing and RNA-sequencing, respectively. Somatic mutations, copy number alterations, mutational signatures and fusion genes were determined with state-of-the-art bioinformatics methods. Our analyses revealed TP53 hotspot mutations associated with loss of heterozygosity of the wild-type allele in two cases. Mutations affecting homologous recombination DNA repair-related genes were found in two cases, and an MLH1 pathogenic germline variant was found in one case. In addition, copy number analysis revealed the presence of a somatic BRCA1 homozygous deletion and focal amplification of 12q14.3-12q21.1, encompassing MDM2, HMGA2, FRS2, and PTPRB. No oncogenic in-frame fusion transcript was identified in the three breast ACCs analysed. CONCLUSIONS: No pathognomonic genetic alterations were detected in the breast ACCs analysed. These tumours have somatic genetic alterations similar to those of common forms of TNBC, and may show homologous recombination deficiency or microsatellite instability. These findings provide further insights into why breast ACCs, which are usually clinically indolent, may evolve into or in parallel with high-grade TNBC.

Assessment of HMGA2 and PLAG1 rearrangements in breast adenomyoepitheliomas.

Breast adenomyoepitheliomas (AMEs) are rare epithelial-myoepithelial neoplasms that may occasionally produce myxochondroid matrix, akin to pleomorphic adenomas (PAs). Regardless of their anatomic location, PAs often harbor rearrangements involving HMGA2 or PLAG1. We have recently shown that the repertoire of somatic genetic alterations of AMEs varies according to their estrogen receptor (ER) status; whilst the majority of ER-positive AMEs display mutually exclusive PIK3CA or AKT1 hotspot mutations, up to 60% of ER-negative AMEs harbor concurrent HRAS Q61 hotspot mutations and mutations affecting either PIK3CA or PIK3R1. Here, we hypothesized that a subset of AMEs lacking these somatic genetic alterations could be underpinned by oncogenic fusion genes, in particular those involving HMGA2 or PLAG1. Therefore, we subjected 13 AMEs to RNA-sequencing for fusion discovery (n = 5) and/or fluorescence in situ hybridization (FISH) analysis for HMGA2 and PLAG1 rearrangements (n = 13). RNA-sequencing revealed an HMGA2-WIF1 fusion gene in an ER-positive AME lacking HRAS, PIK3CA and AKT1 somatic mutations. This fusion gene, which has been previously described in salivary gland PAs, results in a chimeric transcript composed of exons 1-5 of HMGA2 and exons 3-10 of WIF1. No additional in-frame fusion genes or HMGA2 or PLAG1 rearrangements were identified in the remaining AMEs analyzed. Our results demonstrate that a subset of AMEs lacking mutations affecting HRAS and PI3K pathway-related genes may harbor HMGA2-WIF1 fusion genes, suggesting that a subset of breast AMEs may be genetically related to PAs or that a subset of AMEs may originate in the context of a PA.

The Genomic Landscape of Mucinous Breast Cancer.

Mucinous carcinoma of the breast (MCB) is a rare histologic form of estrogen receptor (ER)-positive/HER2-negative breast cancer (BC) characterized by tumor cells floating in lakes of mucin. We assessed the genomic landscape of 32 MCBs by whole-exome sequencing and/or RNA-sequencing. GATA3 (23.8%), KMT2C (19.0%), and MAP3K1 (14.3%) were the most frequently mutated genes in pure MCBs. In addition, two recurrent but not pathognomonic fusion genes, OAZ1-CSNK1G2 and RFC4-LPP, were detected in 3/31 (9.7%) and 2/31 (6.5%) samples, respectively. Compared with ER-positive/HER2-negative common forms of BC, MCBs displayed lower PIK3CA and TP53 mutation rates and fewer concurrent 1q gains and 16q losses. Clonal decomposition analysis of the mucinous and ductal components independently microdissected from five mixed MCBs revealed that they are clonally related and evolve following clonal selection or parallel evolution. Our findings indicate that MCB represents a genetically distinct ER-positive/HER2-negative form of BC.

Recurrent MED12 exon 2 mutations in benign breast fibroepithelial lesions in adolescents and young adults.

AIMS: Most benign breast fibroepithelial lesions (FEL) in adults harbour recurrent somatic MED12 exon 2 mutations and rare TERT promoter hotspot mutations. We sought to determine the frequency of MED12 exon 2 and TERT promoter hotspot mutations in fibroadenomas (FA) and benign phyllodes tumours (BePT) in adolescents and young adults. METHODS: DNA from 21 consecutive FAs and eight consecutive BePTs in adolescents and young adults was subjected to Sanger sequencing of the exon 2 of MED12 and the TERT promoter hotspot locus. RESULTS: We identified MED12 exon 2 mutations in 62% and 88% of FAs and BePTs, respectively, and no TERT promoter hotspot mutations. The majority of the MED12 exon 2 mutations identified were in-frame deletions (60%). CONCLUSIONS: As in adults, benign FELs in juvenile patients harbour recurrent MED12 exon 2 mutations.

Loss-of-function mutations in ATP6AP1 and ATP6AP2 in granular cell tumors.

Granular cell tumors (GCTs) are rare tumors that can arise in multiple anatomical locations, and are characterized by abundant intracytoplasmic granules. The genetic drivers of GCTs are currently unknown. Here, we apply whole-exome sequencing and targeted sequencing analysis to reveal mutually exclusive, clonal, inactivating somatic mutations in the endosomal pH regulators ATP6AP1 or ATP6AP2 in 72% of GCTs. Silencing of these genes in vitro results in impaired vesicle acidification, redistribution of endosomal compartments, and accumulation of intracytoplasmic granules, recapitulating the cardinal phenotypic characteristics of GCTs and providing a novel genotypic-phenotypic correlation. In addition, depletion of ATP6AP1 or ATP6AP2 results in the acquisition of oncogenic properties. Our results demonstrate that inactivating mutations of ATP6AP1 and ATP6AP2 are likely oncogenic drivers of GCTs and underpin the genesis of the intracytoplasmic granules that characterize them, providing a genetic link between endosomal pH regulation and tumorigenesis.

Solid papillary breast carcinomas resembling the tall cell variant of papillary thyroid neoplasms (solid papillary carcinomas with reverse polarity) harbour recurrent mutations affecting IDH2 and PIK3CA: a validation cohort.

AIMS: Solid papillary breast carcinoma resembling the tall cell variant of papillary thyroid neoplasms (BPTC), also known as solid papillary carcinoma with reverse polarity, is a rare histological type of breast cancer that resembles morphologically the tall cell variant of papillary thyroid carcinoma. BPTCs are characterised by IDH2 R172 hotspot somatic mutations or mutually exclusive TET2 somatic mutations, concurrently with mutations affecting PI3K pathway-related genes. We sought to characterise their histology and investigate the frequency of IDH2 and PIK3CA mutations in an independent cohort of BPTCs, as well as in conventional solid papillary carcinomas (SPCs). METHODS AND RESULTS: Six BPTCs, not previously analysed molecularly, and 10 SPCs were reviewed centrally. Tumour DNA was extracted from microdissected histological sections and subjected to Sanger sequencing of the IDH2 R172 hotspot locus and exons 9 and 20 of PIK3CA. All six BPTCs were characterised by solid, papillary and follicular architecture with circumscribed, invasive tumour nodules composed of epithelial cells with reverse polarity. IDH2 mutations were identified in all six BPTCs (three R172S, two R172T and one R172G), four of which also harboured PIK3CA mutations (two H1047R, one Q546K and one Q546R). By contrast, all SPCs lacked IDH2 mutations, while one of 10 harboured a PIK3CA mutation (H1047R). CONCLUSION: We validated the presence of IDH2 R172 hotspot mutations and PIK3CA hotspot mutations in 100% and 67% BPTCs tested, respectively, and documented absence of IDH2 R172 mutations in SPCs. These findings confirm the genotypical-phenotypical correlation reported previously in BPTC, which constitutes an entity distinct from conventional SPC.

MYBL1 rearrangements and MYB amplification in breast adenoid cystic carcinomas lacking the MYB-NFIB fusion gene.

Breast adenoid cystic carcinoma (AdCC), a rare type of triple-negative breast cancer, has been shown to be driven by MYB pathway activation, most often underpinned by the MYB-NFIB fusion gene. Alternative genetic mechanisms, such as MYBL1 rearrangements, have been reported in MYB-NFIB-negative salivary gland AdCCs. Here we report on the molecular characterization by massively parallel sequencing of four breast AdCCs lacking the MYB-NFIB fusion gene. In two cases, we identified MYBL1 rearrangements (MYBL1-ACTN1 and MYBL1-NFIB), which were associated with MYBL1 overexpression. A third AdCC harboured a high-level MYB amplification, which resulted in MYB overexpression at the mRNA and protein levels. RNA-sequencing and whole-genome sequencing revealed no definite alternative driver in the fourth AdCC studied, despite high levels of MYB expression and the activation of pathways similar to those activated in MYB-NFIB-positive AdCCs. In this case, a deletion encompassing the last intron and part of exon 15 of MYB, including the binding site of ERG-1, a transcription factor that may downregulate MYB, and the exon 15 splice site, was detected. In conclusion, we demonstrate that MYBL1 rearrangements and MYB amplification probably constitute alternative genetic drivers of breast AdCCs, functioning through MYBL1 or MYB overexpression. These observations emphasize that breast AdCCs probably constitute a convergent phenotype, whereby activation of MYB and MYBL1 and their downstream targets can be driven by the MYB-NFIB fusion gene, MYBL1 rearrangements, MYB amplification, or other yet to be identified mechanisms. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.