CRISPR screens identify genomic ribonucleotides as a source of PARP-trapping lesions.

The observation that BRCA1- and BRCA2-deficient cells are sensitive to inhibitors of poly(ADP-ribose) polymerase (PARP) has spurred the development of cancer therapies that use these inhibitors to target deficiencies in homologous recombination1. The cytotoxicity of PARP inhibitors depends on PARP trapping, the formation of non-covalent protein-DNA adducts composed of inhibited PARP1 bound to DNA lesions of unclear origins1-4. To address the nature of such lesions and the cellular consequences of PARP trapping, we undertook three CRISPR (clustered regularly interspersed palindromic repeats) screens to identify genes and pathways that mediate cellular resistance to olaparib, a clinically approved PARP inhibitor1. Here we present a high-confidence set of 73 genes, which when mutated cause increased sensitivity to PARP inhibitors. In addition to an expected enrichment for genes related to homologous recombination, we discovered that mutations in all three genes encoding ribonuclease H2 sensitized cells to PARP inhibition. We establish that the underlying cause of the PARP-inhibitor hypersensitivity of cells deficient in ribonuclease H2 is impaired ribonucleotide excision repair5. Embedded ribonucleotides, which are abundant in the genome of cells deficient in ribonucleotide excision repair, are substrates for cleavage by topoisomerase 1, resulting in PARP-trapping lesions that impede DNA replication and endanger genome integrity. We conclude that genomic ribonucleotides are a hitherto unappreciated source of PARP-trapping DNA lesions, and that the frequent deletion of RNASEH2B in metastatic prostate cancer and chronic lymphocytic leukaemia could provide an opportunity to exploit these findings therapeutically.

IL-23 secreted by myeloid cells drives castration-resistant prostate cancer.

Patients with prostate cancer frequently show resistance to androgen-deprivation therapy, a condition known as castration-resistant prostate cancer (CRPC). Acquiring a better understanding of the mechanisms that control the development of CRPC remains an unmet clinical need. The well-established dependency of cancer cells on the tumour microenvironment indicates that the microenvironment might control the emergence of CRPC. Here we identify IL-23 produced by myeloid-derived suppressor cells (MDSCs) as a driver of CRPC in mice and patients with CRPC. Mechanistically, IL-23 secreted by MDSCs can activate the androgen receptor pathway in prostate tumour cells, promoting cell survival and proliferation in androgen-deprived conditions. Intra-tumour MDSC infiltration and IL-23 concentration are increased in blood and tumour samples from patients with CRPC. Antibody-mediated inactivation of IL-23 restored sensitivity to androgen-deprivation therapy in mice. Taken together, these results reveal that MDSCs promote CRPC by acting in a non-cell autonomous manner. Treatments that block IL-23 can oppose MDSC-mediated resistance to castration in prostate cancer and synergize with standard therapies.

Mapping genetic vulnerabilities reveals BTK as a novel therapeutic target in oesophageal cancer.

OBJECTIVE: Oesophageal cancer is the seventh most common cause of cancer-related death worldwide. Disease relapse is frequent and treatment options are limited. DESIGN: To identify new biomarker-defined therapeutic approaches for patients with oesophageal cancer, we integrated the genomic profiles of 17 oesophageal tumour-derived cell lines with drug sensitivity data from small molecule inhibitor profiling, identifying drug sensitivity effects associated with cancer driver gene alterations. We also interrogated recently described RNA interference screen data for these tumour cell lines to identify candidate genetic dependencies or vulnerabilities that could be exploited as therapeutic targets. RESULTS: By integrating the genomic features of oesophageal tumour cell lines with siRNA and drug screening data, we identified a series of candidate targets in oesophageal cancer, including a sensitivity to inhibition of the kinase BTK in MYC amplified oesophageal tumour cell lines. We found that this genetic dependency could be elicited with the clinical BTK/ERBB2 kinase inhibitor, ibrutinib. In both MYC and ERBB2 amplified tumour cells, ibrutinib downregulated ERK-mediated signal transduction, cMYC Ser-62 phosphorylation and levels of MYC protein, and elicited G1 cell cycle arrest and apoptosis, suggesting that this drug could be used to treat biomarker-selected groups of patients with oesophageal cancer. CONCLUSIONS: BTK represents a novel candidate therapeutic target in oesophageal cancer that can be targeted with ibrutinib. On the basis of this work, a proof-of-concept phase II clinical trial evaluating the efficacy of ibrutinib in patients with MYC and/or ERBB2 amplified advanced oesophageal cancer is currently underway (NCT02884453). TRIAL REGISTRATION NUMBER: NCT02884453; Pre-results.

Somatic complex I disruptive mitochondrial DNA mutations are modifiers of tumorigenesis that correlate with low genomic instability in pituitary adenomas.

Mitochondrial DNA (mtDNA) mutations leading to the disruption of respiratory complex I (CI) have been shown to exhibit anti-tumorigenic effects, at variance with those impairing only the function but not the assembly of the complex, which appear to contribute positively to cancer development. Owing to the challenges in the analysis of the multi-copy mitochondrial genome, it is yet to be determined whether tumour-associated mtDNA lesions occur as somatic modifying factors or as germ-line predisposing elements. Here we investigated the whole mitochondrial genome sequence of 20 pituitary adenomas with oncocytic phenotype and identified pathogenic and/or novel mtDNA mutations in 60% of the cases. Using highly sensitive techniques, namely fluorescent PCR and allele-specific locked nucleic acid quantitative PCR, we identified the most likely somatic nature of these mutations in our sample set, since none of the mutations was detected in the corresponding blood tissue of the patients analysed. Furthermore, we have subjected a series of 48 pituitary adenomas to a high-resolution array comparative genomic hybridization analysis, which revealed that CI disruptive mutations, and the oncocytic phenotype, significantly correlate with low number of chromosomal aberrations in the nuclear genome. We conclude that CI disruptive mutations in pituitary adenomas are somatic modifiers of tumorigenesis most likely contributing not only to the development of oncocytic change, but also to a less aggressive tumour phenotype, as indicated by a stable karyotype.

Whole genome sequencing of matched primary and metastatic acral melanomas.

Next generation sequencing has enabled systematic discovery of mutational spectra in cancer samples. Here, we used whole genome sequencing to characterize somatic mutations and structural variation in a primary acral melanoma and its lymph node metastasis. Our data show that the somatic mutational rates in this acral melanoma sample pair were more comparable to the rates reported in cancer genomes not associated with mutagenic exposure than in the genome of a melanoma cell line or the transcriptome of melanoma short-term cultures. Despite the perception that acral skin is sun-protected, the dominant mutational signature in these samples is compatible with damage due to ultraviolet light exposure. A nonsense mutation in ERCC5 discovered in both the primary and metastatic tumors could also have contributed to the mutational signature through accumulation of unrepaired dipyrimidine lesions. However, evidence of transcription-coupled repair was suggested by the lower mutational rate in the transcribed regions and expressed genes. The primary and the metastasis are highly similar at the level of global gene copy number alterations, loss of heterozygosity and single nucleotide variation (SNV). Furthermore, the majority of the SNVs in the primary tumor were propagated in the metastasis and one nonsynonymous coding SNV and one splice site mutation appeared to arise de novo in the metastatic lesion.

Characterization of the genomic features and expressed fusion genes in micropapillary carcinomas of the breast.

Micropapillary carcinoma (MPC) is a rare histological special type of breast cancer, characterized by an aggressive clinical behaviour and a pattern of copy number aberrations (CNAs) distinct from that of grade- and oestrogen receptor (ER)-matched invasive carcinomas of no special type (IC-NSTs). The aims of this study were to determine whether MPCs are underpinned by a recurrent fusion gene(s) or mutations in 273 genes recurrently mutated in breast cancer. Sixteen MPCs were subjected to microarray-based comparative genomic hybridization (aCGH) analysis and Sequenom OncoCarta mutation analysis. Eight and five MPCs were subjected to targeted capture and RNA sequencing, respectively. aCGH analysis confirmed our previous observations about the repertoire of CNAs of MPCs. Sequencing analysis revealed a spectrum of mutations similar to those of luminal B IC-NSTs, and recurrent mutations affecting mitogen-activated protein kinase family genes and NBPF10. RNA-sequencing analysis identified 17 high-confidence fusion genes, eight of which were validated and two of which were in-frame. No recurrent fusions were identified in an independent series of MPCs and IC-NSTs. Forced expression of in-frame fusion genes (SLC2A1-FAF1 and BCAS4-AURKA) resulted in increased viability of breast cancer cells. In addition, genomic disruption of CDK12 caused by out-of-frame rearrangements was found in one MPC and in 13% of HER2-positive breast cancers, identified through a re-analysis of publicly available massively parallel sequencing data. In vitro analyses revealed that CDK12 gene disruption results in sensitivity to PARP inhibition, and forced expression of wild-type CDK12 in a CDK12-null cell line model resulted in relative resistance to PARP inhibition. Our findings demonstrate that MPCs are neither defined by highly recurrent mutations in the 273 genes tested, nor underpinned by a recurrent fusion gene. Although seemingly private genetic events, some of the fusion transcripts found in MPCs may play a role in maintenance of a malignant phenotype and potentially offer therapeutic opportunities.

Genomic profiling of histological special types of breast cancer.

Histological special types of breast cancer have distinctive morphological features and account for up to 25 % of all invasive breast cancers. We sought to determine whether at the genomic level, histological special types of breast cancer are distinct from grade- and estrogen receptor (ER)-matched invasive carcinomas of no special type (IC-NSTs), and to define genes whose expression correlates with gene copy number in histological special types of breast cancer. We characterized 59 breast cancers of ten histological special types using array-based comparative genomic hybridization (aCGH). Hierarchical clustering revealed that the patterns of gene copy number aberrations segregated with ER-status and histological grade, and that samples from each of the breast cancer histological special types preferentially clustered together. We confirmed the patterns of gene copy number aberrations previously reported for lobular, micropapillary, metaplastic, and mucinous carcinomas. On the other hand, metaplastic and medullary carcinomas were found to have genomic profiles similar to those of grade- and ER-matched IC-NSTs. The genomic aberrations observed in invasive carcinomas with osteoclast-like stromal giant cells support its classification as IC-NST variant. Integrative aCGH and gene expression analysis led to the identification of 145 transcripts that were significantly overexpressed when amplified in histological special types of breast cancer. Our results illustrate that together with histological grade and ER-status, histological type is also associated with the patterns and complexity of gene copy number aberrations in breast cancer, with adenoid cystic and mucinous carcinomas being examples of ER-negative and ER-positive breast cancers with distinctive repertoires of gene copy number aberrations.

Mutation profiling of adenoid cystic carcinomas from multiple anatomical sites identifies mutations in the RAS pathway, but no KIT mutations.

AIMS: The majority of adenoid cystic carcinomas (AdCCs), regardless of anatomical site, harbour the MYB-NFIB fusion gene. The aim of this study was to characterize the repertoire of somatic genetic events affecting known cancer genes in AdCCs. METHODS AND RESULTS: DNA was extracted from 13 microdissected breast AdCCs, and subjected to a mutation survey using the Sequenom OncoCarta Panel v1.0. Genes found to be mutated in any of the breast AdCCs and genes related to the same canonical molecular pathways, as well as KIT, a proto-oncogene whose protein product is expressed in AdCCs, were sequenced in an additional 68 AdCCs from various anatomical sites by Sanger sequencing. Using the Sequenom MassARRAY platform and Sanger sequencing, mutations in BRAF and HRAS were identified in three and one cases, respectively (breast, and head and neck). KIT, which has previously been reported to be mutated in AdCCs, was also investigated, but no mutations were identified. CONCLUSIONS: Our results demonstrate that mutations in genes pertaining to the canonical RAS pathway are found in a minority of AdCCs, and that activating KIT mutations are either absent or remarkably rare in these cancers, and unlikely to constitute a driver and therapeutic target for patients with AdCC.

Genomic and mutational profiling of ductal carcinomas in situ and matched adjacent invasive breast cancers reveals intra-tumour genetic heterogeneity and clonal selection.

The mechanisms underlying the progression from ductal carcinoma in situ (DCIS) to invasive ductal carcinoma (IDC) of the breast are yet to be fully elucidated. Several hypotheses have been put forward to explain the progression from DCIS to IDC, including the selection of a subpopulation of cancer cells with specific genetic aberrations, and the acquisition of new genetic aberrations or non-genetic mechanisms mediated by the tumour microenvironment. To determine whether synchronously diagnosed ipsilateral DCI and IDCs have modal populations with distinct repertoires of gene copy number aberrations and mutations in common oncogenes, matched frozen samples of DCIS and IDC were retrieved from 13 patients and subjected to microarray-based comparative genomic hybridization (aCGH) and Sequenom MassARRAY (Oncocarta v 1.0 panel). Fluorescence in situ hybridization and Sanger sequencing were employed to validate the aCGH and Sequenom findings, respectively. Although the genomic profiles of matched DCI and IDCs were similar, in three of 13 matched pairs amplification of distinct loci (ie 1q41, 2q24.2, 6q22.31, 7q11.21, 8q21.2 and 9p13.3) was either restricted to, or more prevalent in, the modal population of cancer cells of one of the components. Sequenom MassARRAY identified PIK3CA mutations restricted to the DCIS component in two cases, and in a third case the frequency of the PIK3CA mutant allele reduced from 49% in the DCIS to 25% in the IDC component. Despite the genomic similarities between synchronous DCIS and IDC, our data provide strong circumstantial evidence to suggest that in some cases the progression from DCIS to IDC is driven by the selection of non-modal clones that harbour a specific repertoire of genetic aberrations.

Adenoid cystic carcinomas constitute a genomically distinct subgroup of triple-negative and basal-like breast cancers.

Adenoid cystic carcinoma (AdCC) is a rare form of triple-negative and basal-like breast cancer that has an indolent clinical behaviour. Four breast AdCCs were recently shown to harbour the recurrent chromosomal translocation t(6;9)(q22-23;p23-24), which leads to the formation of the MYB-NFIB fusion gene. Our aims were (i) to determine the prevalence of the MYB-NFIB fusion gene in AdCCs of the breast; (ii) to characterize the gene copy number aberrations found in AdCCs; and (iii) to determine whether AdCCs are genomically distinct from histological grade-matched or triple-negative and basal-like invasive ductal carcinomas of no special type (IDC-NSTs). The presence of the MYB-NFIB fusion gene was investigated in 13 AdCCs of the breast by fluorescence in situ hybridization (FISH) and reverse transcriptase-PCR (RT-PCR), and MYB and BRCA1 RNA expression was determined by quantitative RT-PCR. Fourteen AdCCs, 14 histological grade-matched IDC-NSTs, and 14 IDC-NSTs of triple-negative and basal-like phenotype were microdissected and subjected to high-resolution microarray-based comparative genomic hybridization (aCGH). The MYB-NFIB fusion gene was detected in all but one AdCC. aCGH analysis demonstrated a relatively low number of copy number aberrations and a lack of recurrent amplifications in breast AdCCs. Contrary to grade-matched IDC-NSTs, AdCCs lacked 1q gains and 16q losses, and in contrast with basal-like IDC-NSTs, AdCCs displayed fewer gene copy number aberrations and expressed MYB and BRCA1 at significantly higher levels. Breast AdCCs constitute an entity distinct from grade-matched and triple-negative and basal-like IDC-NSTs, emphasizing the importance of histological subtyping of triple-negative and basal-like breast carcinomas.

Immunophenotypic and genomic characterization of papillary carcinomas of the breast.

Papillary carcinomas are a special histological type of breast cancer and have a relatively good outcome. We characterized the genomic and phenotypic characteristics of papillary carcinomas to determine whether they would constitute an entity distinct from grade- and oestrogen receptor (ER)-matched invasive ductal carcinomas of no special type (IDC-NSTs). The phenotype of 63 papillary carcinomas of the breast and grade- and ER-matched IDC-NSTs was determined by immunohistochemistry. DNA of sufficient quality was extracted from 49 microdissected papillary carcinomas and 49 microdissected grade- and ER-matched IDC-NSTs. These samples were subjected to high-resolution microarray-based comparative genomic hybridization (aCGH) and Sequenom MassARRAY sequencing analysis of 19 known oncogenes. Papillary carcinomas were predominantly of low histological grade, expressed immunohistochemical markers consistent with a luminal phenotype, and a lower rate of lymph node metastasis and p53 expression than grade- and ER-matched IDC-NSTs. Papillary carcinomas displayed less genomic aberrations than grade- and ER-matched IDC-NSTs; however, the patterns of gene copy number aberrations found in papillary carcinomas were similar to those of ER- and grade-matched IDC-NSTs, including 16q losses. Furthermore, PIK3CA mutations were found in 43% and 29% of papillary carcinomas and grade- and ER-matched IDC-NSTs, respectively. The genomic profiles of encapsulated, solid and invasive papillary carcinomas, the three morphological subtypes, were remarkably similar. Our results demonstrate that papillary carcinomas are a homogeneous special histological type of breast cancer. The similarities in the genomic profiles of papillary carcinomas and grade- and ER-matched IDC-NSTs suggest that papillary carcinomas may be best positioned as part of the spectrum of ER-positive breast cancers, rather than as a distinct entity. Furthermore, the good prognosis of papillary carcinomas may stem from the low rates of lymph node metastasis and p53 expression, low number of gene copy number aberrations and high prevalence of PIK3CA mutations.

A whole-genome massively parallel sequencing analysis of BRCA1 mutant oestrogen receptor-negative and -positive breast cancers.

BRCA1 encodes a tumour suppressor protein that plays pivotal roles in homologous recombination (HR) DNA repair, cell-cycle checkpoints, and transcriptional regulation. BRCA1 germline mutations confer a high risk of early-onset breast and ovarian cancer. In more than 80% of cases, tumours arising in BRCA1 germline mutation carriers are oestrogen receptor (ER)-negative; however, up to 15% are ER-positive. It has been suggested that BRCA1 ER-positive breast cancers constitute sporadic cancers arising in the context of a BRCA1 germline mutation rather than being causally related to BRCA1 loss-of-function. Whole-genome massively parallel sequencing of ER-positive and ER-negative BRCA1 breast cancers, and their respective germline DNAs, was used to characterize the genetic landscape of BRCA1 cancers at base-pair resolution. Only BRCA1 germline mutations, somatic loss of the wild-type allele, and TP53 somatic mutations were recurrently found in the index cases. BRCA1 breast cancers displayed a mutational signature consistent with that caused by lack of HR DNA repair in both ER-positive and ER-negative cases. Sequencing analysis of independent cohorts of hereditary BRCA1 and sporadic non-BRCA1 breast cancers for the presence of recurrent pathogenic mutations and/or homozygous deletions found in the index cases revealed that DAPK3, TMEM135, KIAA1797, PDE4D, and GATA4 are potential additional drivers of breast cancers. This study demonstrates that BRCA1 pathogenic germline mutations coupled with somatic loss of the wild-type allele are not sufficient for hereditary breast cancers to display an ER-negative phenotype, and has led to the identification of three potential novel breast cancer genes (ie DAPK3, TMEM135, and GATA4).

Functional characterization of the 19q12 amplicon in grade III breast cancers.

INTRODUCTION: The 19q12 locus is amplified in a subgroup of oestrogen receptor (ER)-negative grade III breast cancers. This amplicon comprises nine genes, including cyclin E1 (CCNE1), which has been proposed as its 'driver'. The aim of this study was to identify the genes within the 19q12 amplicon whose expression is required for the survival of cancer cells harbouring their amplification. METHODS: We investigated the presence of 19q12 amplification in a series of 313 frozen primary breast cancers and 56 breast cancer cell lines using microarray comparative genomic hybridisation (aCGH). The nine genes mapping to the smallest region of amplification on 19q12 were silenced using RNA interference in phenotypically matched breast cancer cell lines with (MDA-MB-157 and HCC1569) and without (Hs578T, MCF7, MDA-MB-231, ZR75.1, JIMT1 and BT474) amplification of this locus. Genes whose silencing was selectively lethal in amplified cells were taken forward for further validation. The effects of cyclin-dependent kinase 2 (CDK2) silencing and chemical inhibition were tested in cancer cells with and without CCNE1 amplification. RESULTS: 19q12 amplification was identified in 7.8% of ER-negative grade III breast cancer. Of the nine genes mapping to this amplicon, UQCRFS1, POP4, PLEKHF1, C19ORF12, CCNE1 and C19ORF2 were significantly over-expressed when amplified in primary breast cancers and/or breast cancer cell lines. Silencing of POP4, PLEKHF1, CCNE1 and TSZH3 selectively reduced cell viability in cancer cells harbouring their amplification. Cancer cells with CCNE1 amplification were shown to be dependent on CDK2 expression and kinase activity for their survival. CONCLUSIONS: The 19q12 amplicon may harbour more than a single 'driver', given that expression of POP4, PLEKHF1, CCNE1 and TSZH3 is required for the survival of cancer cells displaying their amplification. The observation that cancer cells harbouring CCNE1 gene amplification are sensitive to CDK2 inhibitors provides a rationale for the testing of these chemical inhibitors in a subgroup of patients with ER-negative grade III breast cancers.

Genomic profiling of mitochondrion-rich breast carcinoma: chromosomal changes may be relevant for mitochondria accumulation and tumour biology.

Oncocytic carcinomas are composed of mitochondrion-rich cells. Though recognised by the WHO classification as a histological special type of breast cancer, their status as a discrete pathological entity remains a matter of contention. Given that oncocytic tumours of other anatomical sites display distinct clinico-pathological and molecular features, we sought to define the molecular genetic features of mitochondrion-rich breast tumours and to compare them with a series of histological grade- and oestrogen receptor status-matched invasive ductal carcinomas of no special type. Seventeen mitochondrion-rich breast carcinomas, including nine bona fide oncocytic carcinomas, were profiled with antibodies against oestrogen, progesterone and androgen receptors, HER2, Ki67, GCDFP-15, chromogranin, epithelial membrane antigen, cytokeratin 7, cytokeratin 14, CD68 and mitochondria antigen. These tumours were microdissected and DNA extracted from samples with >70% of tumour cells. Fourteen cases yielded DNA of sufficient quality/quantity and were subjected to high-resolution microarray comparative genomic hybridisation analysis. The genomic profiles were compared to those of 28 grade- and oestrogen receptor status-matched invasive ductal carcinomas of no special type. Oncocytic and other mitochondrion-rich tumours did not differ significantly between themselves. As a group, mitochondrion-rich carcinomas were immunophenotypically heterogenous. Recurrent copy number changes were similar to those described in unselected breast cancers. However, unsupervised and supervised analysis identified a subset of mitochondrion-rich cancers, which often displayed gains of 11q13.1-q13.2 and 19p13. Changes in the latter two chromosomal regions have been shown to be associated with oncocytic tumours of the kidney and thyroid, respectively, and host several nuclear genes with specific mitochondrial function. Our results indicate that in a way akin to oncocytic tumours of other anatomical sites, at least a subset of mitochondrion-rich breast carcinomas may be underpinned by a distinct pattern of chromosomal changes potentially relevant for mitochondria accumulation and constitute a discrete molecular entity.

Non-existence of caveolin-1 gene mutations in human breast cancer.

Caveolin-1 is the principal constituent protein of caveolae, which are specialised plasma membrane invaginations with diverse biological roles. Caveolin-1 is suggested to have tumour suppressive functions and CAV1 gene mutations have been reported in 20% of breast cancers. The aim of the present study was to evaluate the frequency of CAV1 mutations in a large cohort of optimally accrued breast cancers. Two independent series of breast cancer samples were analysed: 82 fresh-frozen grade 3 and 158 formalin-fixed paraffin-embedded invasive ductal carcinomas of no special type were consecutively accrued and subjected to microdissection of neoplastic epithelial cells prior to DNA extraction. Thirty-nine human breast cancer cell lines were also included in this study. The trans-membrane region of CAV1 and adjacent sequences, where mutations are reported to cluster, were amplified by PCR, followed by direct sequencing and mutational analysis. None of the reported CAV1 gene mutations, including CAV1 (P132L), were identified in either clinical samples (95% CI: 0-1.5%) or human breast cancer cell lines analysed. One novel non-synonymous germline polymorphism was detected within a reported region of high mutational frequency. This study does not corroborate the reported frequent occurrence of CAV1 gene mutations, including CAV1 (P132L), in primary human breast carcinomas. Our findings demonstrate that if CAV1 mutations do exist, their overall mutational frequency is substantially lower than positive reports have suggested. Taken together with other studies, which have also failed to identify CAV1 mutations, our data call into question the existence and biological and clinical relevance of CAV1 gene mutations in human breast cancer.

Molecular evidence in support of the neoplastic and precursor nature of microglandular adenosis.

AIMS: Microglandular adenosis (MGA) is a proliferative breast lesion, which has been proposed to be a potential precursor of triple-negative breast cancers. The aims of this study were to determine whether MGAs harbour genetic alterations and if any such genetic aberrations found in MGAs are similar to those found in matched invasive carcinomas. METHODS AND RESULTS: Twelve cases of MGA and/or atypical MGA (AMGA), 10 of which were associated with invasive carcinoma, were evaluated. Immunohistochemical profiling revealed that all invasive carcinomas were of triple-negative phenotype and expressed S100, cytokeratins 8/18 and 'basal' markers. The morphologically distinct components of each case (MGA, AMGA and/or invasive carcinoma) were microdissected and subjected to microarray comparative genomic hybridization. Apart from three typical MGAs, all samples harboured genetic alterations. The percentage of the genome affected by copy number aberrations in MGA/AMGA ranged from 0.5 to 61.9%, indicating varying levels of genetic instability. In three cases, MGA/AMGA displayed copy number aberrations similar to those found in matched invasive components, providing strong circumstantial evidence that MGA may constitute the substrate for the invasive carcinoma development. CONCLUSIONS: Our results support the contention that MGA can be a clonal lesion and non-obligate precursor of triple-negative breast cancer.

Functional characterization of EMSY gene amplification in human cancers.

The 11q13-q14 locus is frequently amplified in human cancers, with a complex structure harbouring multiple potential oncogenic drivers. The EMSY gene has been proposed as a driver of the third core of the 11q13-q14 amplicon. This gene encodes a protein reported to be a BRCA2-binding partner, which when over-expressed would lead to impairment of BRCA2 functions and could constitute a mechanism for BRCA2 inactivation in non-hereditary breast and ovarian cancers. We hypothesized that if EMSY amplification abrogates BRCA2 functions, cells harbouring this aberration would be unable to elicit competent homologous recombination DNA repair and, therefore, may have increased sensitivity to genotoxic therapies and potent PARP inhibitors. Microarray-based comparative genomic hybridization of cell lines from distinct tumour sites, including breast, ovary, pancreas, oesophagus, lung and the oral cavity, led to the identification of 10 cell lines with EMSY amplification and 18 without. EMSY amplification was shown to correlate with EMSY mRNA levels, although not all cell lines harbouring EMSY amplification displayed EMSY mRNA or protein over-expression. RNA interference-mediated silencing of EMSY did not lead to a reduction in cell viability in tumour models harbouring EMSY amplification. Cell lines with and without EMSY amplification displayed a similar ability to elicit RAD51 foci in response to DNA damaging agents, and similar sensitivity to cisplatin and olaparib. Taken together, this suggests that EMSY is unlikely to be a driver of the 11q13-q14 amplicon and does not have a dominant role in modulating the response to agents targeting cells with defective homologous recombination.

High-throughput detection of fusion genes in cancer using the Sequenom MassARRAY platform.

Fusion genes have pivotal roles in the development and progression of human cancer and offer potential for rational drug design. Massively parallel sequencing has identified a panoply of in-frame expressed fusion genes, but early reports suggest that the majority of these are present at very low prevalence or are private events. Conventional methods for the identification of recurrent expressed fusion genes in large cohorts of cancers (eg fluorescence in situ hybridization (FISH) and reverse transcriptase PCR (RT-PCR)) are time consuming and prone to artifacts. Here, we describe a novel high-throughput strategy for the detection of recurrent fusion genes in cancer based on the Sequenom MassARRAY platform. Fusion genes were initially identified by massively parallel sequencing of breast cancer cell lines. For each fusion gene, two Sequenom probes were designed. Primary human breast cancers and cancer cell lines were interrogated for 10 fusion genes. Sensitivity, specificity, and predictive values of the MassARRAY method were then determined using FISH and qRT-PCR as the 'gold standard.' By combining two probes per fusion gene, the negative and positive predictive values were 100 and 71.4%, respectively. All fusion genes identified by massively parallel sequencing were accurately detected. No recurrent fusion genes were found. The MassARRAY-based approach described here may, therefore, be employed as a high-throughput screening tool for known fusion genes in human cancer. In keeping with other highly sensitive assays, further refinement of this technique is necessary to reduce the number of false-positive results.

ß-Catenin pathway activation in breast cancer is associated with triple-negative phenotype but not with CTNNB1 mutation.

Aberrant ß-catenin expression as determined by assessment of its subcellular localization constitutes a surrogate marker of Wnt signalling pathway activation and has been reported in a subset of breast cancers. The association of ß-catenin/Wnt pathway activation with clinical outcome and the mechanisms leading to its activation in breast cancers still remain a matter of controversy. The aims of this study were to address the distribution of ß-catenin expression in invasive breast cancers, the correlations between ß-catenin expression and clinicopathological features and survival of breast cancer patients, and to determine whether aberrant ß-catenin expression is driven by CTNNB1 (ß-catenin encoding gene) activating mutations. Immunohistochemistry was performed on a tissue microarray containing 245 invasive breast carcinomas from uniformly treated patients, using two anti-ß-catenin monoclonal antibodies. Selected samples were subjected to CTNNB1 exon 3 mutation analysis by direct gene sequencing. A good correlation between the two ß-catenin antibodies was observed (Spearman's r >0.62, P<0.001). Respectively, 31 and 11% of the cases displayed lack/reduction of ß-catenin membranous expression and nuclear accumulation. Complete lack of ß-catenin expression was significantly associated with invasive lobular carcinoma histological type. Subgroup analysis of non-lobular cancers or non-lobular grade 3 carcinomas revealed that lack/reduction of ß-catenin membranous expression and/or nuclear accumulation were significantly associated with oestrogen receptor negativity, absence of HER2 gene amplification and overexpression, lack/reduction of E-cadherin expression and tumours of triple-negative and basal-like phenotype. Univariate survival analysis revealed a significant association between ß-catenin nuclear expression and shorter metastasis-free and overall survival in the whole cohort; however, ß-catenin nuclear expression was not an independent predictor of outcome in multivariate analysis. No CTNNB1 mutations were identified in the 28 selected breast carcinomas analysed. In conclusion, ß-catenin/Wnt pathway activation is preferentially found in triple-negative/basal-like breast carcinomas, is associated with poor clinical outcome and is unlikely to be driven by CTNNB1 mutations in breast cancer.

Mucinous carcinoma of the breast is genomically distinct from invasive ductal carcinomas of no special type.

Mucinous carcinomas are a rare entity accounting for up to 2% of all breast cancers, which have been shown to display a gene expression profile distinct from that of invasive ductal carcinomas of no special type (IDC-NSTs). Here, we have defined the genomic aberrations that are characteristic of this special type of breast cancer and have investigated whether mucinous carcinomas might constitute a genomic entity distinct from IDC-NSTs. Thirty-five pure and 11 mixed mucinous breast carcinomas were assessed by immunohistochemistry using antibodies against oestrogen receptor (ER), progesterone receptor, HER2, Ki67, cyclin D1, cortactin, Bcl-2, p53, E-cadherin, basal markers, neuroendocrine markers, and WT1. Fifteen pure mucinous carcinomas and 30 grade- and ER-matched IDC-NSTs were microdissected and subjected to high-resolution microarray-based comparative genomic hybridization (aCGH). In addition, the distinct components of seven mixed mucinous carcinomas were microdissected separately and subjected to aCGH. Pure mucinous carcinomas consistently expressed ER (100%), lacked HER2 expression (97.1%), and showed a relatively low level of genetic instability. Unsupervised hierarchical cluster analysis revealed that pure mucinous carcinomas were homogeneous and preferentially clustered together, separately from IDC-NSTs. They less frequently harboured gains of 1q and 16p and losses of 16q and 22q than grade- and ER-matched IDC-NSTs, and no pure mucinous carcinoma displayed concurrent 1q gain and 16q loss, a hallmark genetic feature of low-grade IDC-NSTs. Finally, both components of all but one mixed mucinous carcinoma displayed similar patterns of genetic aberrations and preferentially clustered together with pure mucinous carcinomas on unsupervised clustering analysis. Our results demonstrate that mucinous carcinomas are more homogeneous between themselves at the genetic level than IDC-NSTs. Both components of mixed mucinous tumours are remarkably similar at the molecular level to pure mucinous cancers, suggesting that mixed mucinous carcinomas may be best classified as variants of mucinous cancers rather than of IDC-NSTs.