ESMO expert consensus statements (ECS) on the definition, diagnosis, and management of HER2-low breast cancer.

Human epidermal growth factor receptor 2 (HER2)-low breast cancer has recently emerged as a targetable subset of breast tumors, based on the evidence from clinical trials of novel anti-HER2 antibody-drug conjugates. This evolution has raised several biological and clinical questions, warranting the establishment of consensus to optimally treat patients with HER2-low breast tumors. Between 2022 and 2023, the European Society for Medical Oncology (ESMO) held a virtual consensus-building process focused on HER2-low breast cancer. The consensus included a multidisciplinary panel of 32 leading experts in the management of breast cancer from nine different countries. The aim of the consensus was to develop statements on topics that are not covered in detail in the current ESMO Clinical Practice Guideline. The main topics identified for discussion were (i) biology of HER2-low breast cancer; (ii) pathologic diagnosis of HER2-low breast cancer; (iii) clinical management of HER2-low metastatic breast cancer; and (iv) clinical trial design for HER2-low breast cancer. The expert panel was divided into four working groups to address questions relating to one of the four topics outlined above. A review of the relevant scientific literature was conducted in advance. Consensus statements were developed by the working groups and then presented to the entire panel for further discussion and amendment before voting. This article presents the developed statements, including findings from the expert panel discussions, expert opinion, and a summary of evidence supporting each statement.

APOBEC mutagenesis, kataegis, chromothripsis in EGFR-mutant osimertinib-resistant lung adenocarcinomas.

BACKGROUND: Studies of targeted therapy resistance in lung cancer have primarily focused on single-gene alterations. Based on prior work implicating apolipoprotein b mRNA-editing enzyme, catalytic polypeptide-like (APOBEC) mutagenesis in histological transformation of epidermal growth factor receptor (EGFR)-mutant lung cancers, we hypothesized that mutational signature analysis may help elucidate acquired resistance to targeted therapies. PATIENTS AND METHODS: APOBEC mutational signatures derived from an Food and Drug Administration-cleared multigene panel [Memorial Sloan Kettering Cancer Center Integrated Mutation Profiling of Actionable Cancer Targets (MSK-IMPACT)] using the Signature Multivariate Analysis (SigMA) algorithm were validated against the gold standard of mutational signatures derived from whole-exome sequencing. Mutational signatures were decomposed in 3276 unique lung adenocarcinomas (LUADs), including 93 paired osimertinib-naïve and -resistant EGFR-mutant tumors. Associations between APOBEC and mechanisms of resistance to osimertinib were investigated. Whole-genome sequencing was carried out on available EGFR-mutant lung cancer samples (10 paired, 17 unpaired) to investigate large-scale genomic alterations potentially contributing to osimertinib resistance. RESULTS: APOBEC mutational signatures were more frequent in receptor tyrosine kinase (RTK)-driven lung cancers (EGFR, ALK, RET, and ROS1; 25%) compared to LUADs at large (20%, P < 0.001); across all subtypes, APOBEC mutational signatures were enriched in subclonal mutations (P < 0.001). In EGFR-mutant lung cancers, osimertinib-resistant samples more frequently displayed an APOBEC-dominant mutational signature compared to osimertinib-naïve samples (28% versus 14%, P = 0.03). Specifically, mutations detected in osimertinib-resistant tumors but not in pre-treatment samples significantly more frequently displayed an APOBEC-dominant mutational signature (44% versus 23%, P < 0.001). EGFR-mutant samples with APOBEC-dominant signatures had enrichment of large-scale genomic rearrangements (P = 0.01) and kataegis (P = 0.03) in areas of APOBEC mutagenesis. CONCLUSIONS: APOBEC mutational signatures are frequent in RTK-driven LUADs and increase under the selective pressure of osimertinib in EGFR-mutant lung cancer. APOBEC mutational signature enrichment in subclonal mutations, private mutations acquired after osimertinib treatment, and areas of large-scale genomic rearrangements highlights a potentially fundamental role for APOBEC mutagenesis in the development of resistance to targeted therapies, which may be potentially exploited to overcome such resistance.

ESMO recommendations on the use of circulating tumour DNA assays for patients with cancer: a report from the ESMO Precision Medicine Working Group.

Circulating tumour DNA (ctDNA) assays conducted on plasma are rapidly developing a strong evidence base for use in patients with cancer. The European Society for Medical Oncology convened an expert working group to review the analytical and clinical validity and utility of ctDNA assays. For patients with advanced cancer, validated and adequately sensitive ctDNA assays have utility in identifying actionable mutations to direct targeted therapy, and may be used in routine clinical practice, provided the limitations of the assays are taken into account. Tissue-based testing remains the preferred test for many cancer patients, due to limitations of ctDNA assays detecting fusion events and copy number changes, although ctDNA assays may be routinely used when faster results will be clinically important, or when tissue biopsies are not possible or inappropriate. Reflex tumour testing should be considered following a non-informative ctDNA result, due to false-negative results with ctDNA testing. In patients treated for early-stage cancers, detection of molecular residual disease or molecular relapse, has high evidence of clinical validity in anticipating future relapse in many cancers. Molecular residual disease/molecular relapse detection cannot be recommended in routine clinical practice, as currently there is no evidence for clinical utility in directing treatment. Additional potential applications of ctDNA assays, under research development and not recommended for routine practice, include identifying patients not responding to therapy with early dynamic changes in ctDNA levels, monitoring therapy for the development of resistance mutations before clinical progression, and in screening asymptomatic people for cancer. Recommendations for reporting of results, future development of ctDNA assays and future clinical research are made.

Comprehensive assessment of germline pathogenic variant detection in tumor-only sequencing.

BACKGROUND: Tumor-only sequencing, implemented for the identification of somatic variants, is oftentimes used for the detection of actionable germline variants. We sought to determine whether tumor-only sequencing assays are suitable for detection of actionable germline variants, given their importance for the delivery of targeted therapies and risk-reducing measures. PATIENTS AND METHODS: The detection of germline variants affecting moderate- and high-penetrance cancer susceptibility genes (CSGs) by tumor-only sequencing was compared to clinical germline testing in 21 333 cancer patients who underwent tumor and germline testing using the Food and Drug Administration (FDA)-authorized Memorial Sloan Kettering-Integrated Mutation Profiling of Actionable Targets (MSK-IMPACT) assay. Seven homologous recombination deficiency (HRD), two DNA damage response (DDR) and four mismatch repair (MMR) genes, as well as NF1, RB1 and TP53 were included in the analysis. FDA-authorized and New York State Department of Health-approved sequencing methods for germline, tumor/normal and tumor-only sequencing assays and analytical pipelines were employed. RESULTS: In patients who underwent tumor and germline sequencing, as compared to clinical genetic testing, tumor-only sequencing failed to detect 10.5% of clinically actionable pathogenic germline variants in CSGs, including 18.8%, 12.8% and 7.3% of germline variants in MMR, DDR and HRD genes, respectively. The sensitivity for detection of pathogenic germline variants by tumor-only sequencing was 89.5%. Whilst the vast majority of pathogenic germline exonic single-nucleotide variants (SNVs) and small indels were detected by tumor-only sequencing, large percentages of germline copy number variants, intronic variants and repetitive element insertions were not detected. CONCLUSIONS: Tumor-only sequencing is adequate for the detection of clinically actionable germline variants, particularly for SNVs and small indels; however, a small subset of alterations affecting HRD, DDR and MMR genes may not be detected optimally. Therefore, for high-risk patients with negative tumor-only sequencing results, clinical genetic testing could be considered given the impact of these variants on therapy and genetic counseling.

ESMO recommendations on the standard methods to detect RET fusions and mutations in daily practice and clinical research.

Aberrant activation of RET is a critical driver of growth and proliferation in diverse solid tumours. Multikinase inhibitors (MKIs) showing anti-RET activities have been tested in RET-altered tumours with variable results. The low target specificity with consequent increase in side-effects and off-target toxicities resulting in dose reduction and drug discontinuation are some of the major issues with MKIs. To overcome these issues, new selective RET inhibitors such as pralsetinib (BLU-667) and selpercatinib (LOXO-292) have been developed in clinical trials, with selpercatinib recently approved by the Food and Drug Administration (FDA). The results of these trials showed marked and durable antitumour activity and manageable toxicity profiles in patients with RET-altered tumours. The European Society for Medical Oncology (ESMO) Translational Research and Precision Medicine Working Group (TR and PM WG) launched a collaborative project to review the available methods for the detection of RET gene alterations, their potential applications and strategies for the implementation of a rational approach for the detection of RET fusion genes and mutations in human malignancies. We present here recommendations for the routine clinical detection of targetable RET rearrangements and mutations.

Recommendations for the use of next-generation sequencing (NGS) for patients with metastatic cancers: a report from the ESMO Precision Medicine Working Group.

Next-generation sequencing (NGS) allows sequencing of a high number of nucleotides in a short time frame at an affordable cost. While this technology has been widely implemented, there are no recommendations from scientific societies about its use in oncology practice. The European Society for Medical Oncology (ESMO) is proposing three levels of recommendations for the use of NGS. Based on the current evidence, ESMO recommends routine use of NGS on tumour samples in advanced non-squamous non-small-cell lung cancer (NSCLC), prostate cancers, ovarian cancers and cholangiocarcinoma. In these tumours, large multigene panels could be used if they add acceptable extra cost compared with small panels. In colon cancers, NGS could be an alternative to PCR. In addition, based on the KN158 trial and considering that patients with endometrial and small-cell lung cancers should have broad access to anti-programmed cell death 1 (anti-PD1) antibodies, it is recommended to test tumour mutational burden (TMB) in cervical cancers, well- and moderately-differentiated neuroendocrine tumours, salivary cancers, thyroid cancers and vulvar cancers, as TMB-high predicted response to pembrolizumab in these cancers. Outside the indications of multigene panels, and considering that the use of large panels of genes could lead to few clinically meaningful responders, ESMO acknowledges that a patient and a doctor could decide together to order a large panel of genes, pending no extra cost for the public health care system and if the patient is informed about the low likelihood of benefit. ESMO recommends that the use of off-label drugs matched to genomics is done only if an access programme and a procedure of decision has been developed at the national or regional level. Finally, ESMO recommends that clinical research centres develop multigene sequencing as a tool to screen patients eligible for clinical trials and to accelerate drug development, and prospectively capture the data that could further inform how to optimise the use of this technology.

ESMO recommendations on the standard methods to detect NTRK fusions in daily practice and clinical research.

BACKGROUND: NTRK1, NTRK2 and NTRK3 fusions are present in a plethora of malignancies across different histologies. These fusions represent the most frequent mechanism of oncogenic activation of these receptor tyrosine kinases, and biomarkers for the use of TRK small molecule inhibitors. Given the varying frequency of NTRK1/2/3 fusions, crucial to the administration of NTRK inhibitors is the development of optimal approaches for the detection of human cancers harbouring activating NTRK1/2/3 fusion genes. MATERIALS AND METHODS: Experts from several Institutions were recruited by the European Society for Medical Oncology (ESMO) Translational Research and Precision Medicine Working Group (TR and PM WG) to review the available methods for the detection of NTRK gene fusions, their potential applications, and strategies for the implementation of a rational approach for the detection of NTRK1/2/3 fusion genes in human malignancies. A consensus on the most reasonable strategy to adopt when screening for NTRK fusions in oncologic patients was sought, and further reviewed and approved by the ESMO TR and PM WG and the ESMO leadership. RESULTS: The main techniques employed for NTRK fusion gene detection include immunohistochemistry, fluorescence in situ hybridization (FISH), RT-PCR, and both RNA-based and DNA-based next generation sequencing (NGS). Each technique has advantages and limitations, and the choice of assays for screening and final diagnosis should also take into account the resources and clinical context. CONCLUSION: In tumours where NTRK fusions are highly recurrent, FISH, RT-PCR or RNA-based sequencing panels can be used as confirmatory techniques, whereas in the scenario of testing an unselected population where NTRK1/2/3 fusions are uncommon, either front-line sequencing (preferentially RNA-sequencing) or screening by immunohistochemistry followed by sequencing of positive cases should be pursued.

Ultra-deep next-generation sequencing of plasma cell-free DNA in patients with advanced lung cancers: results from the Actionable Genome Consortium.

BACKGROUND: Noninvasive genotyping using plasma cell-free DNA (cfDNA) has the potential to obviate the need for some invasive biopsies in cancer patients while also elucidating disease heterogeneity. We sought to develop an ultra-deep plasma next-generation sequencing (NGS) assay for patients with non-small-cell lung cancers (NSCLC) that could detect targetable oncogenic drivers and resistance mutations in patients where tissue biopsy failed to identify an actionable alteration. PATIENTS AND METHODS: Plasma was prospectively collected from patients with advanced, progressive NSCLC. We carried out ultra-deep NGS using cfDNA extracted from plasma and matched white blood cells using a hybrid capture panel covering 37 lung cancer-related genes sequenced to 50 000× raw target coverage filtering somatic mutations attributable to clonal hematopoiesis. Clinical sensitivity and specificity for plasma detection of known oncogenic drivers were calculated and compared with tissue genotyping results. Orthogonal ddPCR validation was carried out in a subset of cases. RESULTS: In 127 assessable patients, plasma NGS detected driver mutations with variant allele fractions ranging from 0.14% to 52%. Plasma ddPCR for EGFR or KRAS mutations revealed findings nearly identical to those of plasma NGS in 21 of 22 patients, with high concordance of variant allele fraction (r = 0.98). Blinded to tissue genotype, plasma NGS sensitivity for de novo plasma detection of known oncogenic drivers was 75% (68/91). Specificity of plasma NGS in those who were driver-negative by tissue NGS was 100% (19/19). In 17 patients with tumor tissue deemed insufficient for genotyping, plasma NGS identified four KRAS mutations. In 23 EGFR mutant cases with acquired resistance to targeted therapy, plasma NGS detected potential resistance mechanisms, including EGFR T790M and C797S mutations and ERBB2 amplification. CONCLUSIONS: Ultra-deep plasma NGS with clonal hematopoiesis filtering resulted in de novo detection of targetable oncogenic drivers and resistance mechanisms in patients with NSCLC, including when tissue biopsy was inadequate for genotyping.

A combinatorial biomarker predicts pathologic complete response to neoadjuvant lapatinib and trastuzumab without chemotherapy in patients with HER2+ breast cancer.

BACKGROUND: HER2-positive (+) breast cancers, defined by HER2 overexpression and/or amplification, are often addicted to HER2 to maintain their malignant phenotype. Yet, some HER2+ tumors do not benefit from anti-HER2 therapy. We hypothesize that HER2 amplification levels and PI3K pathway activation are key determinants of response to HER2-targeted treatments without chemotherapy. PATIENTS AND METHODS: Baseline HER2+ tumors from patients treated with neoadjuvant lapatinib plus trastuzumab [with endocrine therapy for estrogen receptor (ER)+ tumors] in TBCRC006 (NCT00548184) were evaluated in a central laboratory for HER2 amplification by fluorescence in situ hybridization (FISH) (n = 56). HER2 copy number (CN) and FISH ratios, and PI3K pathway status, defined by PIK3CA mutations or PTEN levels by immunohistochemistry were available for 41 tumors. Results were correlated with pathologic complete response (pCR; no residual invasive tumor in breast). RESULTS: Thirteen of the 56 patients (23%) achieved pCR. None of the 11 patients with HER2 ratio <4 and/or CN <10 achieved pCR, whereas 13/45 patients (29%) with HER2 ratio ≥4 and/or CN ≥10 attained pCR (P = 0.0513). Of the 18 patients with tumors expressing high PTEN or wild-type (WT) PIK3CA (intact PI3K pathway), 7 (39%) achieved pCR, compared with 1/23 (4%) with PI3K pathway alterations (P = 0.0133). Seven of the 16 patients (44%) with HER2 ratio ≥4 and intact PI3K pathway achieved pCR, whereas only 1/25 (4%) patients not meeting these criteria achieved pCR (P = 0.0031). CONCLUSIONS: Our findings suggest that there is a clinical subtype in breast cancer with high HER2 amplification and intact PI3K pathway that is especially sensitive to HER2-targeted therapies without chemotherapy. A combination of HER2 FISH ratio and PI3K pathway status warrants validation to identify patients who may be treated with HER2-targeted therapy without chemotherapy.

The European Society for Medical Oncology (ESMO) Precision Medicine Glossary.

Background: Precision medicine is rapidly evolving within the field of oncology and has brought many new concepts and terminologies that are often poorly defined when first introduced, which may subsequently lead to miscommunication within the oncology community. The European Society for Medical Oncology (ESMO) recognises these challenges and is committed to support the adoption of precision medicine in oncology. To add clarity to the language used by oncologists and basic scientists within the context of precision medicine, the ESMO Translational Research and Personalised Medicine Working Group has developed a standardised glossary of relevant terms. Materials and methods: Relevant terms for inclusion in the glossary were identified via an ESMO member survey conducted in Autumn 2016, and by the ESMO Translational Research and Personalised Medicine Working Group members. Each term was defined by experts in the field, discussed and, if necessary, modified by the Working Group before reaching consensus approval. A literature search was carried out to determine which of the terms, 'precision medicine' and 'personalised medicine', is most appropriate to describe this field. Results: A total of 43 terms are included in the glossary, grouped into five main themes-(i) mechanisms of decision, (ii) characteristics of molecular alterations, (iii) tumour characteristics, (iv) clinical trials and statistics and (v) new research tools. The glossary classes 'precision medicine' or 'personalised medicine' as technically interchangeable but the term 'precision medicine' is favoured as it more accurately reflects the highly precise nature of new technologies that permit base pair resolution dissection of cancer genomes and is less likely to be misinterpreted. Conclusions: The ESMO Precision Medicine Glossary provides a resource to facilitate consistent communication in this field by clarifying and raising awareness of the language employed in cancer research and oncology practice. The glossary will be a dynamic entity, undergoing expansion and refinement over the coming years.

Compromised BRCA1-PALB2 interaction is associated with breast cancer risk.

The major breast cancer suppressor proteins BRCA1 and BRCA2 play essential roles in homologous recombination (HR)-mediated DNA repair, which is thought to be critical for tumor suppression. The two BRCA proteins are linked by a third tumor suppressor, PALB2, in the HR pathway. While truncating mutations in these genes are generally pathogenic, interpretation of missense variants remains a challenge. To date, patient-derived missense variants that disrupt PALB2 binding have been identified in BRCA1 and BRCA2; however, there has not been sufficient evidence to prove their pathogenicity in humans, and no variants in PALB2 that disrupt either its BRCA1 or BRCA2 binding have been reported. Here we report on the identification of a novel PALB2 variant, c.104T>C (p.L35P), that segregates in a family with a strong history of breast cancer. Functional analyses showed that L35P abrogates the PALB2-BRCA1 interaction and completely disables its abilities to promote HR and confer resistance to platinum salts and PARP inhibitors. Whole-exome sequencing of a breast cancer from a c.104T>C carrier revealed a second, somatic, truncating mutation affecting PALB2, and the tumor displays hallmark genomic features of tumors with BRCA mutations and HR defects, cementing the pathogenicity of L35P. Parallel analyses of other germline variants in the PALB2 N-terminal BRCA1-binding domain identified multiple variants that affect HR function to varying degrees, suggesting their possible contribution to cancer development. Our findings establish L35P as the first pathogenic missense mutation in PALB2 and directly demonstrate the requirement of the PALB2-BRCA1 interaction for breast cancer suppression.

Mechanism of action of a WWTR1(TAZ)-CAMTA1 fusion oncoprotein.

The WWTR1 (protein is known as TAZ)-CAMTA1 (WC) fusion gene defines epithelioid hemangioendothelioma, a malignant vascular cancer. TAZ (transcriptional coactivator with PDZ binding motif) is a transcriptional coactivator and end effector of the Hippo tumor suppressor pathway. It is inhibited by phosphorylation by the Hippo kinases LATS1 and LATS2. Such phosphorylation causes cytoplasmic localization, 14-3-3 protein binding and the phorphorylation of a terminal phosphodegron promotes ubiquitin-dependent degradation (the phosphorylation of the different motifs has several effects). CAMTA1 is a putative tumor suppressive transcription factor. Here we demonstrate that TAZ-CAMTA1 (TC) fusion results in its nuclear localization and constitutive activation. Consequently, cells expressing TC display a TAZ-like transcriptional program that causes resistance to anoikis and oncogenic transformation. Our findings elucidate the mechanistic basis of TC oncogenic properties, highlight that TC is an important model to understand how the Hippo pathway can be inhibited in cancer, and provide approaches for targeting this chimeric protein.

Response to dual HER2 blockade in a patient with HER3-mutant metastatic breast cancer.

BACKGROUND: HER3 activating mutations have been shown in preclinical models to be oncogenic and ligand-independent, but to depend on kinase-active HER2. PATIENTS AND METHODS: Whole-exome sequencing of the primary HER2-negative breast cancer and its HER2-negative synchronous liver metastasis from a 46-year-old female revealed the presence of an activating and clonal HER3 G284R mutation. RESULTS: HER2 dual blockade with trastuzumab and lapatinib as third-line therapy led to complete metabolic response in 2 weeks and confirmed radiological partial response after 8 weeks. Following the resection of the liver metastasis, the patient remains disease-free 40 weeks after initiation of the HER2 dual blockade therapy. Immunohistochemical analysis demonstrated a substantial reduction of phospho-rpS6 and phospho-AKT in the post-therapy biopsy of the liver metastasis. DISCUSSION: This is the first-in-man evidence that anti-HER2 therapies are likely effective in breast cancers harboring HER3 activating mutations.

The evaluation of tumor-infiltrating lymphocytes (TILs) in breast cancer: recommendations by an International TILs Working Group 2014.

BACKGROUND: The morphological evaluation of tumor-infiltrating lymphocytes (TILs) in breast cancer (BC) is gaining momentum as evidence strengthens for the clinical relevance of this immunological biomarker. Accumulating evidence suggests that the extent of lymphocytic infiltration in tumor tissue can be assessed as a major parameter by evaluation of hematoxylin and eosin (H&E)-stained tumor sections. TILs have been shown to provide prognostic and potentially predictive value, particularly in triple-negative and human epidermal growth factor receptor 2-overexpressing BC. DESIGN: A standardized methodology for evaluating TILs is now needed as a prerequisite for integrating this parameter in standard histopathological practice, in a research setting as well as in clinical trials. This article reviews current data on the clinical validity and utility of TILs in BC in an effort to foster better knowledge and insight in this rapidly evolving field, and to develop a standardized methodology for visual assessment on H&E sections, acknowledging the future potential of molecular/multiplexed approaches. CONCLUSIONS: The methodology provided is sufficiently detailed to offer a uniformly applied, pragmatic starting point and improve consistency and reproducibility in the measurement of TILs for future studies.

Capturing intra-tumor genetic heterogeneity by de novo mutation profiling of circulating cell-free tumor DNA: a proof-of-principle.

BACKGROUND: Plasma-derived cell-free tumor DNA (ctDNA) constitutes a potential surrogate for tumor DNA obtained from tissue biopsies. We posit that massively parallel sequencing (MPS) analysis of ctDNA may help define the repertoire of mutations in breast cancer and monitor tumor somatic alterations during the course of targeted therapy. PATIENT AND METHODS: A 66-year-old patient presented with synchronous estrogen receptor-positive/HER2-negative, highly proliferative, grade 2, mixed invasive ductal-lobular carcinoma with bone and liver metastases at diagnosis. DNA extracted from archival tumor material, plasma and peripheral blood leukocytes was subjected to targeted MPS using a platform comprising 300 cancer genes known to harbor actionable mutations. Multiple plasma samples were collected during the fourth line of treatment with an AKT inhibitor. RESULTS: Average read depths of 287x were obtained from the archival primary tumor, 139x from the liver metastasis and between 200x and 900x from ctDNA samples. Sixteen somatic non-synonymous mutations were detected in the liver metastasis, of which 9 (CDKN2A, AKT1, TP53, JAK3, TSC1, NF1, CDH1, MML3 and CTNNB1) were also detected in >5% of the alleles found in the primary tumor sample. Not all mutations identified in the metastasis were reliably identified in the primary tumor (e.g. FLT4). Analysis of ctDNA, nevertheless, captured all mutations present in the primary tumor and/or liver metastasis. In the longitudinal monitoring of the patient, the mutant allele fractions identified in ctDNA samples varied over time and mirrored the pharmacodynamic response to the targeted therapy as assessed by positron emission tomography-computed tomography. CONCLUSIONS: This proof-of-principle study is one of the first to demonstrate that high-depth targeted MPS of plasma-derived ctDNA constitutes a potential tool for de novo mutation identification and monitoring of somatic genetic alterations during the course of targeted therapy, and may be employed to overcome the challenges posed by intra-tumor genetic heterogeneity. REGISTERED CLINICAL TRIAL: www.clinicaltrials.gov, NCT01090960.

Biomarker changes associated with the development of resistance to aromatase inhibitors (AIs) in estrogen receptor-positive breast cancer.

BACKGROUND: The purpose of this study was to identify any differences in key biomarkers associated with estrogen action between biopsies taken at diagnosis and at recurrence or progression during treatment with an aromatase inhibitor (AI). PATIENTS AND METHODS: Patients were retrospectively identified from a clinical database as having relapsed or progressed during AI treatment. Immunohistochemistry was carried out against estrogen receptor (ER), progesterone receptor (PgR), human epidermal growth factor receptor 2 (HER2), insulin-like growth factor type-1 receptor (IGF1R), insulin receptor substrate-1 (IRS-1), stathmin, phosphatase and tensin homolog and Ki67. RESULTS: Fifty-five pairs of samples were identified with ER- and/or PgR-positive diseases. Four (7%) patients were ER-negative at progression. Overall, PgR levels were lower in the recurrence sample, but 35% of cases remained positive. IGF1R levels decreased significantly. There were no substantial changes in HER2, IRS-1 or stathmin levels to indicate a role in resistance. Higher Ki67 levels at resistance indicate more proliferative disease. CONCLUSIONS: The phenotype of AI-recurrent lesions shows high between-tumour heterogeneity. There is evidence of an increase in Ki67, a reduction in IGF1R and a loss of ER expression in some individuals and some activation of growth factor signalling pathways that may explain resistance in individuals and merit treatment targeted to those pathways. Biopsy at recurrence will be necessary to identify the relevant target for individuals.

Integrative molecular and functional profiling of ERBB2-amplified breast cancers identifies new genetic dependencies.

Overexpression of the receptor tyrosine kinase ERBB2 (also known as HER2) occurs in around 15% of breast cancers and is driven by amplification of the ERBB2 gene. ERBB2 amplification is a marker of poor prognosis, and although anti-ERBB2-targeted therapies have shown significant clinical benefit, de novo and acquired resistance remains an important problem. Genomic profiling has demonstrated that ERBB2+ve breast cancers are distinguished from ER+ve and 'triple-negative' breast cancers by harbouring not only the ERBB2 amplification on 17q12, but also a number of co-amplified genes on 17q12 and amplification events on other chromosomes. Some of these genes may have important roles in influencing clinical outcome, and could represent genetic dependencies in ERBB2+ve cancers and therefore potential therapeutic targets. Here, we describe an integrated genomic, gene expression and functional analysis to determine whether the genes present within amplicons are critical for the survival of ERBB2+ve breast tumour cells. We show that only a fraction of the ERBB2-amplified breast tumour lines are truly addicted to the ERBB2 oncogene at the mRNA level and display a heterogeneous set of additional genetic dependencies. These include an addiction to the transcription factor gene TFAP2C when it is amplified and overexpressed, suggesting that TFAP2C represents a genetic dependency in some ERBB2+ve breast cancer cells.

Identification of novel determinants of resistance to lapatinib in ERBB2-amplified cancers.

The gene encoding the receptor tyrosine kinase ERBB2, also known as HER2, is amplified and/or overexpressed in up to 15% of breast cancers. These tumours are characterised by an aggressive phenotype and poor clinical outcome. Although therapies targeted at ERBB2 have proven effective, many patients fail to respond to treatment or become resistant and the reasons for this are still largely unknown. Using a high-throughput functional screen we assessed whether genes found to be recurrently amplified and overexpressed in ERBB2+ve breast cancers mediate resistance to the ERBB2-targeted agent lapatinib. Lapatinib-resistant ERBB2-amplified breast cancer cell lines were screened, in the presence or absence of lapatinib, with an RNA interference library targeting 369 genes recurrently amplified and overexpressed in both ERBB2-amplified breast cancer tumours and cell lines. Small interfering RNAs targeting a number of genes caused sensitivity to lapatinib in this context. The mechanisms of resistance conferred by the identified genes were further investigated and in the case of NIBP (TRAPPC9), lapatinib resistance was found to be mediated through NF-κB signalling. Our results indicate that specific amplified and/ or overexpressed genes found in ERBB2-amplified breast cancer may mediate response to ERBB2-targeting agents.