Optimal targeting of PI3K-AKT and mTOR in advanced oestrogen receptor-positive breast cancer.

The growing availability of targeted therapies for patients with advanced oestrogen receptor-positive breast cancer has improved survival, but there remains much to learn about the optimal management of these patients. The PI3K-AKT and mTOR pathways are among the most commonly activated pathways in breast cancer, whose crucial role in the pathogenesis of this tumour type has spurred major efforts to target this pathway at specific kinase hubs. Approvals for oestrogen receptor-positive advanced breast cancer include the PI3K inhibitor alpelisib for PIK3CA-mutated tumours, the AKT inhibitor capivasertib for tumours with alterations in PIK3CA, AKT1, or PTEN, and the mTOR inhibitor everolimus, which is used irrespective of mutation status. The availability of different inhibitors leaves physicians with a potentially challenging decision over which of these therapies should be used for individual patients and when. In this Review, we present a comprehensive summary of our current understanding of the pathways and the three inhibitors and discuss strategies for the optimal sequencing of therapies in the clinic, particularly after progression on a CDK4/6 inhibitor.

Management of patients with advanced-stage HER2-positive breast cancer: current evidence and future perspectives.

Amplification and/or overexpression of ERBB2, the gene encoding HER2, can be found in 15-20% of invasive breast cancers and is associated with an aggressive phenotype and poor clinical outcomes. Relentless research efforts in molecular biology and drug development have led to the implementation of several HER2-targeted therapies, including monoclonal antibodies, tyrosine-kinase inhibitors and antibody-drug conjugates, constituting one of the best examples of bench-to-bedside translation in oncology. Each individual drug class has improved patient outcomes and, importantly, the combinatorial and sequential use of different HER2-targeted therapies has increased cure rates in the early stage disease setting and substantially prolonged survival for patients with advanced-stage disease. In this Review, we describe key steps in the development of the modern paradigm for the treatment of HER2-positive advanced-stage breast cancer, including selecting and sequencing new-generation HER2-targeted therapies, and summarize efficacy and safety outcomes from pivotal studies. We then outline the factors that are currently known to be related to resistance to HER2-targeted therapies, such as HER2 intratumoural heterogeneity, activation of alternative signalling pathways and immune escape mechanisms, as well as potential strategies that might be used in the future to overcome this resistance and further improve patient outcomes.

Nonlobular Invasive Breast Carcinomas with Biallelic Pathogenic CDH1 Somatic Alterations: A Histologic, Immunophenotypic, and Genomic Characterization.

CDH1 encodes for E-cadherin, and its loss of function is the hallmark of invasive lobular carcinoma (ILC). Albeit vanishingly rare, biallelic CDH1 alterations may be found in nonlobular breast carcinomas (NL-BCs). We sought to determine the clinicopathologic characteristics and repertoire of genetic alterations of NL-BCs harboring CDH1 biallelic genetic alterations. Analysis of 5842 breast cancers (BCs) subjected to clinical tumor-normal sequencing with an FDA-cleared multigene panel was conducted to identify BCs with biallelic CDH1 pathogenic/likely pathogenic somatic mutations lacking lobular features. The genomic profiles of NL-BCs with CDH1 biallelic genetic alterations were compared with those of ILCs and invasive ductal carcinomas (IDCs), matched by clinicopathologic characteristics. Of the 896 CDH1-altered BCs, 889 samples were excluded based on the diagnosis of invasive mixed ductal/lobular carcinoma or ILC or the detection of monoallelic CDH1 alterations. Only 7 of the 5842 (0.11%) BCs harbored biallelic CDH1 alterations and lacked lobular features. Of these, 4/7 (57%) cases were ER-positive/HER2-negative, 1/7 (14%) was ER-positive/HER2-positive, and 2/7 (29%) were ER-negative/HER2-negative. In total, 5/7 (71%) were of Nottingham grade 2, and 2/7 (29%) were of grade 3. The NL-BCs with CDH1 biallelic genetic alterations included a mucinous carcinoma (n = 1), IDCs with focal nested growth (n = 2), IDC with solid papillary (n = 1) or apocrine (n = 2) features, and an IDC of no special type (NST; n = 1). E-cadherin expression, as detected by immunohistochemistry, was absent (3/5) or aberrant (discontinuous membranous/cytoplasmic/granular; 2/5). However, NL-BCs with CDH1 biallelic genetic alterations displayed recurrent genetic alterations, including TP53, PIK3CA (57%, 4/7; each), FGFR1, and NCOR1 (28%, 2/7, each) alterations. Compared with CDH1 wild-type IDC-NSTs, NL-BCs less frequently harbored GATA3 mutations (0% vs 47%, P = .03), but no significant differences were detected when compared with matched ILCs. Therefore, NL-BCs with CDH1 biallelic genetic alterations are vanishingly rare, predominantly comprise IDCs with special histologic features, and have genomic features akin to luminal B ER-positive BCs.

Somatic estrogen receptor α mutations that induce dimerization promote receptor activity and breast cancer proliferation.

Physiologic activation of estrogen receptor α (ERα) is mediated by estradiol (E2) binding in the ligand-binding pocket of the receptor, repositioning helix 12 (H12) to facilitate binding of coactivator proteins in the unoccupied coactivator binding groove. In breast cancer, activation of ERα is often observed through point mutations that lead to the same H12 repositioning in the absence of E2. Through expanded genetic sequencing of breast cancer patients, we identified a collection of mutations located far from H12 but nonetheless capable of promoting E2-independent transcription and breast cancer cell growth. Using machine learning and computational structure analyses, this set of mutants was inferred to act distinctly from the H12-repositioning mutants and instead was associated with conformational changes across the ERα dimer interface. Through both in vitro and in-cell assays of full-length ERα protein and isolated ligand-binding domain, we found that these mutants promoted ERα dimerization, stability, and nuclear localization. Point mutations that selectively disrupted dimerization abrogated E2-independent transcriptional activity of these dimer-promoting mutants. The results reveal a distinct mechanism for activation of ERα function through enforced receptor dimerization and suggest dimer disruption as a potential therapeutic strategy to treat ER-dependent cancers.

ESR1 F404 Mutations and Acquired Resistance to Fulvestrant in ESR1-Mutant Breast Cancer.

Fulvestrant is used to treat patients with hormone receptor-positive advanced breast cancer, but acquired resistance is poorly understood. PlasmaMATCH Cohort A (NCT03182634) investigated the activity of fulvestrant in patients with activating ESR1 mutations in circulating tumor DNA (ctDNA). Baseline ESR1 mutations Y537S are associated with poor outcomes and Y537C with good outcomes. Sequencing of baseline and EOT ctDNA samples (n = 69) revealed 3/69 (4%) patients acquired novel ESR1 F404 mutations (F404L, F404I, and F404V), in cis with activating mutations. In silico modeling revealed that ESR1 F404 contributes to fulvestrant binding to estrogen receptor-alpha (ERα) through a pi-stacking bond, with mutations disrupting this bond. In vitro analysis demonstrated that single F404L, E380Q, and D538G models were less sensitive to fulvestrant, whereas compound mutations D538G + F404L and E380Q + F404L were resistant. Several oral ERα degraders were active against compound mutant models. We have identified a resistance mechanism specific to fulvestrant that can be targeted by treatments in clinical development. SIGNIFICANCE: Novel F404 ESR1 mutations may be acquired to cause overt resistance to fulvestrant when combined with preexisting activating ESR1 mutations. Novel combinations of mutations in the ER ligand binding domain may cause drug-specific resistance, emphasizing the potential of similar drug-specific mutations to impact the efficacy of oral ER degraders in development. This article is featured in Selected Articles from This Issue, p. 201.

Incidence of HER2-expressing brain metastases in patients with HER2-null breast cancer: a matched case analysis.

The HER2-directed antibody-drug conjugate trastuzumab deruxtecan is active against lower levels of HER2 expression than prior-generation therapies. The rate of HER2 expression in brain metastases among patients with initially HER2-null breast cancer is undefined, and receptor discordance in advanced breast cancer with brain metastases may underestimate CNS response potential in the absence of brain metastasis sampling. In this cohort study including 136 patients with 401 samples scored according to ASCO/CAP guidelines, 15/28 patients (54%) with HER2-null primary breast cancer have detectable HER2 expression in subsequently resected brain metastases, a significant discordant population.

Sequential activation of E2F via Rb degradation and c-Myc drives resistance to CDK4/6 inhibitors in breast cancer.

Cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) are key therapeutic agents in the management of metastatic hormone-receptor-positive breast cancer. However, the emergence of drug resistance limits their long-term efficacy. Here, we show that breast cancer cells develop CDK4/6i resistance via a sequential two-step process of E2F activation. This process entails retinoblastoma (Rb)-protein degradation, followed by c-Myc-mediated amplification of E2F transcriptional activity. CDK4/6i treatment halts cell proliferation in an Rb-dependent manner but dramatically reduces Rb-protein levels. However, this reduction in Rb levels insufficiently induces E2F activity. To develop CDK4/6i resistance, upregulation or activating mutations in mitogenic or hormone signaling are required to stabilize c-Myc levels, thereby augmenting E2F activity. Our analysis of pre-treatment tumor samples reveals a strong correlation between c-Myc levels, rather than Rb levels, and poor therapeutic outcomes after CDK4/6i treatment. Moreover, we propose that proteasome inhibitors can potentially reverse CDK4/6i resistance by restoring Rb levels.

A Druggable FOXA1-Glucocorticoid Receptor Transcriptional Axis Drives Tumor Growth in a Subset of Non-Small Cell Lung Cancer.

The FOXA1 pioneer factor is an essential mediator of steroid receptor function in multiple hormone-dependent cancers, including breast and prostate cancers, enabling nuclear receptors such as estrogen receptor (ER) and androgen receptor (AR) to activate lineage-specific growth programs. FOXA1 is also highly expressed in non-small cell lung cancer (NSCLC), but whether and how it regulates tumor growth in this context is not known. Analyzing data from loss-of-function screens, we identified a subset of NSCLC tumor lines where proliferation is FOXA1 dependent. Using rapid immunoprecipitation and mass spectrometry of endogenous protein, we identified chromatin-localized interactions between FOXA1 and glucocorticoid receptor (GR) in these tumor cells. Knockdown of GR inhibited proliferation of FOXA1-dependent, but not FOXA1-independent NSCLC cells. In these FOXA1-dependent models, FOXA1 and GR cooperate to regulate gene targets involved in EGF signaling and G1-S cell-cycle progression. To investigate the therapeutic potential for targeting this complex, we examined the effects of highly selective inhibitors of the GR ligand-binding pocket and found that GR antagonism with ORIC-101 suppressed FOXA1/GR target expression, activation of EGF signaling, entry into the S-phase, and attendant proliferation in vitro and in vivo. Taken together, our findings point to a subset of NSCLCs harboring a dependence on the FOXA1/GR growth program and provide rationale for its therapeutic targeting. Significance: NSCLC is the leading cause of cancer deaths worldwide. There is a need to identify novel druggable dependencies. We identify a subset of NSCLCs dependent on FOXA1-GR and sensitive to GR antagonism.

Therapeutic resistance to anti-oestrogen therapy in breast cancer.

The hormone receptor oestrogen receptor-α (ER) orchestrates physiological mammary gland development, breast carcinogenesis and the progression of breast tumours into lethal, treatment-refractory systemic disease. Selective antagonism of ER signalling has been one of the most successful therapeutic approaches in oncology, benefiting patients as both a cancer preventative measure and a cancer treatment strategy. However, resistance to anti-oestrogen therapy is a major clinical challenge. Over the past decade, we have gained an understanding of how breast cancers evolve under the pressure of anti-oestrogen therapy. This is best depicted by the case of oestrogen-independent mutations in the gene encoding ER (ESR1), which are virtually absent in primary breast cancer but highly prevalent (20-40%) in anti-oestrogen-treated metastatic disease. These and other findings highlight the 'evolvability' of ER+ breast cancer and the need to understand molecular processes by which this evolution occurs. Recent development and approval of next-generation ER antagonists to target ESR1-mutant breast cancer underscores the clinical importance of this evolvability and sets a new paradigm for the treatment of ER+ breast cancers.

An Open-label Phase I Study of GDC-0927 in Postmenopausal Women with Locally Advanced or Metastatic Estrogen Receptor-Positive Breast Cancer.

PURPOSE: GDC-0927 is a novel, potent, nonsteroidal, orally bioavailable, selective estrogen receptor (ER) degrader that induces tumor regression in ER+ breast cancer xenograft models. PATIENTS AND METHODS: This phase I dose-escalation multicenter study enrolled postmenopausal women with ER+/HER2- metastatic breast cancer to determine the safety, pharmacokinetics, and recommended phase II dose of GDC-0927. Pharmacodynamics was assessed with [18F]-fluoroestradiol (FES) PET scans. RESULTS: Forty-two patients received GDC-0927 once daily. The MTD was not reached. The most common adverse events (AE) regardless of causality were nausea, constipation, diarrhea, arthralgia, fatigue, hot flush, back pain, and vomiting. There were no deaths, grade 4/5 AEs, or treatment-related serious AEs. Two patients experienced grade 2 AEs of special interest of deep vein thrombosis and jugular vein thrombosis, both considered unrelated to GDC-0927. Following dosing, approximately 1.6-fold accumulation was observed, consistent with the observed half-life and dosing frequency. There were no complete or partial responses. Pharmacodynamics was supported by >90% reduction in FES uptake and an approximately 40% reduction in ER expression, suggesting ER degradation is not the mechanistic driver of ER antagonism. Twelve patients (29%) achieved clinical benefit; 17 patients (41%) showed a confirmed best overall response of stable disease. Baseline levels of ER and progesterone receptor protein and mutant ESR1 circulating tumor DNA did not correlate with clinical benefit. CONCLUSIONS: GDC-0927 appeared to be well tolerated with pharmacokinetics supporting once-daily dosing. There was evidence of target engagement and preliminary evidence of antitumor activity in heavily pretreated patients with advanced/metastatic ER+/HER2- breast cancer with and without ESR1 mutations.

Rise of Antibody-Drug Conjugates: The Present and Future.

Antibody-drug conjugates (ADCs) embody a simple, but elegant, vision for cancer therapy-the delivery of a potent cytotoxic agent to tumor cells with minimal damage to normal cells-so-called smart chemo. Although there were significant challenges in achieving this milestone culminating in the first Food and Drug Administration approval in 2000, subsequent advancements in technology have led to rapid drug development with regulatory approvals for ADCs targeting a variety of tumor types. The most successful application for solid tumors has been in breast cancer, with ADCs becoming the standard of care across traditional human epidermal growth factor receptor 2 (HER2)+, hormone receptor+ (HR+) and triple-negative disease subtypes. Moreover, the improved features and gains in potency with the development of ADCs have expanded the treatment-eligible population to those with low/heterogeneous expression of the target antigen on the tumor with trastuzumab deruxtecan or in the case of sacituzumab govitecan, agnostic to target expression. Despite their antibody-directed homing, these novel agents come with their share of toxicities obligating appropriate patient selection and vigilant monitoring while on treatment. As more ADCs are included in the treatment armamentarium, mechanisms of resistance need to be studied and understood for optimal sequencing. Modifying the payload to use immune-stimulating agents or combination therapies with immunotherapy and other effective targeted therapies may further extend the utility of these agents in the treatment of solid tumors.

ADCs or: How I Learned to Stop Worrying and Love Chemotherapy.

Antibody-drug conjugates are transforming cancer treatment, and payload characteristics are emerging as crucial determinants of clinical activity. As exemplified by Weng and colleagues, advancements in the linker and payload chemistry may provide the next evolutionary step in enabling this class of drugs to overcome chemoresistance and deliver even more profound responses. See related article by Weng et al., p. 950 (2).

Emerging Therapies for Breast Cancer.

The steady, incremental improvements in outcomes for both early-stage and advanced breast cancer patients are, in large part, attributable to the success of novel systemic therapies. In this review, we discuss key conceptual paradigms that have underpinned this success including (1) targeting the driver: the identification and targeting of major oncoproteins in breast cancers; (2) targeting the lineage pathway: inhibition of those pathways that drive normal mammary epithelial cell proliferation that retain importance in cancer; (3) targeting precisely: the application of molecular classifiers to refine therapy selection for specific cancers, and of antibody-drug conjugates to pinpoint tumor and tumor promoting cells for eradication; and (4) exploiting synthetic lethality: leveraging unique vulnerabilities that cancer-specific molecular alterations induce. We describe promising examples of novel therapies that have been discovered within each of these paradigms and suggest how future drug development efforts might benefit from the continued application of these principles.

ERα-LBD, an isoform of estrogen receptor alpha, promotes breast cancer proliferation and endocrine resistance.

Estrogen receptor alpha (ERα) drives mammary gland development and breast cancer (BC) growth through an evolutionarily conserved linkage of DNA binding and hormone activation functions. Therapeutic targeting of the hormone binding pocket is a widely utilized and successful strategy for breast cancer prevention and treatment. However, resistance to this endocrine therapy is frequently encountered and may occur through bypass or reactivation of ER-regulated transcriptional programs. We now identify the induction of an ERα isoform, ERα-LBD, that is encoded by an alternative ESR1 transcript and lacks the activation function and DNA binding domains. Despite lacking the transcriptional activity, ERα-LBD is found to promote breast cancer growth and resistance to the ERα antagonist fulvestrant. ERα-LBD is predominantly localized to the cytoplasm and mitochondria of BC cells and leads to enhanced glycolysis, respiration and stem-like features. Intriguingly, ERα-LBD expression and function does not appear to be restricted to cancers that express full length ERα but also promotes growth of triple-negative breast cancers and ERα-LBD transcript (ESR1-LBD) is also present in BC samples from both ERα(+) and ERα(-) human tumors. These findings point to ERα-LBD as a potential mediator of breast cancer progression and therapy resistance.

PRC2-Inactivating Mutations in Cancer Enhance Cytotoxic Response to DNMT1-Targeted Therapy via Enhanced Viral Mimicry.

Polycomb repressive complex 2 (PRC2) has oncogenic and tumor-suppressive roles in cancer. There is clinical success of targeting this complex in PRC2-dependent cancers, but an unmet therapeutic need exists in PRC2-loss cancer. PRC2-inactivating mutations are a hallmark feature of high-grade malignant peripheral nerve sheath tumor (MPNST), an aggressive sarcoma with poor prognosis and no effective targeted therapy. Through RNAi screening in MPNST, we found that PRC2 inactivation increases sensitivity to genetic or small-molecule inhibition of DNA methyltransferase 1 (DNMT1), which results in enhanced cytotoxicity and antitumor response. Mechanistically, PRC2 inactivation amplifies DNMT inhibitor-mediated expression of retrotransposons, subsequent viral mimicry response, and robust cell death in part through a protein kinase R (PKR)-dependent double-stranded RNA sensor. Collectively, our observations posit DNA methylation as a safeguard against antitumorigenic cell-fate decisions in PRC2-loss cancer to promote cancer pathogenesis, which can be therapeutically exploited by DNMT1-targeted therapy. SIGNIFICANCE: PRC2 inactivation drives oncogenesis in various cancers, but therapeutically targeting PRC2 loss has remained challenging. Here we show that PRC2-inactivating mutations set up a tumor context-specific liability for therapeutic intervention via DNMT1 inhibitors, which leads to innate immune signaling mediated by sensing of derepressed retrotransposons and accompanied by enhanced cytotoxicity. See related commentary by Guil and Esteller, p. 2020. This article is highlighted in the In This Issue feature, p. 2007.

AMEERA-1 phase 1/2 study of amcenestrant, SAR439859, in postmenopausal women with ER-positive/HER2-negative advanced breast cancer.

AMEERA-1 is a Phase 1/2 open-label single-arm study evaluating once-daily (QD) amcenestrant, an orally bioavailable selective estrogen receptor (ER) degrader, in postmenopausal women with ER+/HER2- advanced breast cancer (NCT03284957), who were mostly heavily pretreated (including targeted therapies and fulvestrant). In the dose escalation phase (Part A: n = 16), patients received amcenestrant 20-600 mg QD. Based on absence of dose-limiting toxicities, paired functional 18F-fluoroestradiol positron emission tomography, and pharmacokinetics, 400 mg QD was selected as recommended Phase 2 dose (RP2D) for the dose expansion phase (Part B: n = 49). No Grade ≥3 treatment-related adverse events or clinically significant cardiac/eye toxicities were reported. The Part B primary endpoint, confirmed objective response rate (ORR) was 3/45 at the interim analysis and 5/46 (10.9%) at the final analysis. The overall clinical benefit rate (CBR) was 13/46 (28.3%). CBRs among patients with baseline wild-type and mutated ESR1 were 9/26 (34.6%) and 4/19 (21.1%), respectively. Paired tumor biopsy and cell-free DNA analyses revealed ER inhibition and degradation, and a reduction in detectable ESR1 mutations, including Y537S. In conclusion, amcenestrant at RP2D of 400 mg QD for monotherapy is well-tolerated with no dose-limiting toxicities, and demonstrates preliminary antitumor activity irrespective of baseline ESR1 mutation status.

Accelerating drug development in breast cancer: New frontiers for ER inhibition.

The estrogen receptor (ER) is an important driver in the proliferation, tumorigenesis, and progression of breast cancers, and targeting ER signaling at different levels is a successful strategy in the control of hormone receptor positive (HR+) breast cancer. Endocrine therapy has been the treatment of choice for HR+ breast cancer in the early and advanced stages with multiple agents, including selective estrogen receptor modulators (SERMS), selective estrogen receptor degraders (SERDs), and aromatase inhibitors (AIs), which vary in their mechanisms of action and pharmacokinetics. Combination strategies also employ cyclin dependent kinase 4 and 6 and phosphatidylinositol 3-kinase to maximize the benefits of endocrine therapy. This paper reviews the clinical development of SERDs and other novel ER inhibitors, as well as combination strategies to overcome mechanisms of ER pathway escape. It also assesses the advantages of newer oral ER inhibitors with increased bioavailability, improved therapeutic index, better administration, and increased efficacy, as well as discussing future directions in the field.

Management of Advanced Human Epidermal Growth Factor Receptor 2-Positive Breast Cancer and Brain Metastases: ASCO Guideline Update.

PURPOSE: To provide updated evidence- and consensus-based guideline recommendations to practicing oncologists and others on the management of brain metastases for patients with human epidermal growth factor receptor 2 (HER2)-positive advanced breast cancer up to 2021. METHODS: An Expert Panel conducted a targeted systematic literature review (for both systemic therapy for non-CNS metastases and for CNS metastases of HER2+ guideline updates) that identified 545 articles. Outcomes of interest included overall survival, progression-free survival, and adverse events. RESULTS: Of the 545 publications identified and reviewed, six on systemic therapy were identified to form the evidentiary basis for the systemic therapy for CNS metastases guideline recommendations. RECOMMENDATIONS: Patients with brain metastases should receive appropriate local therapy and systemic therapy, if indicated. Local therapies include surgery, whole-brain radiotherapy, and stereotactic radiosurgery. Memantine and hippocampal avoidance should be added to whole-brain radiotherapy when possible. Treatments depend on factors such as patient prognosis, presence of symptoms, resectability, number and size of metastases, prior therapy, and whether metastases are diffuse. Other options include systemic therapy, best supportive care, enrollment onto a clinical trial, and/or palliative care. There are insufficient data to recommend for or against performing routine magnetic resonance imaging to screen for brain metastases; clinicians should have a low threshold for magnetic resonance imaging of the brain because of the high incidence of brain metastases among patients with HER2-positive advanced breast cancer.Additional information is available at www.asco.org/breast-cancer-guidelines.

Systemic Therapy for Advanced Human Epidermal Growth Factor Receptor 2-Positive Breast Cancer: ASCO Guideline Update.

PURPOSE: To update evidence-based guideline recommendations to practicing oncologists and others on systemic therapy for patients with human epidermal growth factor receptor 2 (HER2)-positive advanced breast cancer. METHODS: An Expert Panel conducted a targeted systematic literature review (for both systemic treatment and CNS metastases) and identified 545 articles. Outcomes of interest included efficacy and safety. RESULTS: Of the 545 publications identified and reviewed, 14 were identified to form the evidentiary basis for the guideline recommendations. RECOMMENDATIONS: HER2-targeted therapy is recommended for patients with HER2-positive advanced breast cancer, except for those with clinical congestive heart failure or significantly compromised left ventricular ejection fraction, who should be evaluated on a case-by-case basis. Trastuzumab, pertuzumab, and taxane for first-line treatment and trastuzumab deruxtecan for second-line treatment are recommended. In the third-line setting, clinicians should offer other HER2-targeted therapy combinations. There is a lack of head-to-head trials; therefore, there is insufficient evidence to recommend one regimen over another. The patient and the clinician should discuss differences in treatment schedule, route, toxicities, etc during the decision-making process. Options include regimens with tucatinib, trastuzumab emtansine, trastuzumab deruxtecan (if either not previously administered), neratinib, lapatinib, chemotherapy, margetuximab, hormonal therapy, and abemaciclib plus trastuzumab plus fulvestrant, and may offer pertuzumab if the patient has not previously received it. Optimal duration of chemotherapy is at least 4-6 months or until maximum response, depending on toxicity and in the absence of progression. HER2-targeted therapy can continue until time of progression or unacceptable toxicities. For patients with HER2-positive and estrogen receptor-positive or progesterone receptor-positive breast cancer, clinicians may recommend either standard first-line therapy or, for selected patients, endocrine therapy plus HER2-targeted therapy or endocrine therapy alone.Additional information is available at www.asco.org/breast-cancer-guidelines.

Recurrent WWTR1 S89W mutations and Hippo pathway deregulation in clear cell carcinomas of the cervix.

Clear cell carcinoma (CCC) of the cervix (cCCC) is a rare and aggressive type of human papillomavirus (HPV)-negative cervical cancer with limited effective treatment options for recurrent or metastatic disease. Historically, CCCs of the lower genital tract were associated with in utero diethylstilbestrol exposure; however, the genetic landscape of sporadic cCCCs remains unknown. Here we sought to define the molecular underpinning of cCCCs. Using a combination of whole-exome, targeted capture, and RNA-sequencing, we identified pathogenic genetic alterations in the Hippo signaling pathway in 50% (10/20) of cCCCs, including recurrent WWTR1 S89W somatic mutations in 40% (4/10) of the cases harboring mutations in the Hippo pathway. Irrespective of the presence or absence of Hippo pathway genetic alterations, however, all primary cCCCs analyzed in this study (n = 20) harbored features of Hippo pathway deregulation at the transcriptomic and protein levels. In vitro functional analysis revealed that expression of the WWTR1 S89W mutation leads to reduced binding of TAZ to 14-3-3, promoting constitutive nuclear translocation of TAZ and Hippo pathway repression. WWTR1 S89W expression was found to lead to acquisition of oncogenic behavior, including increased proliferation, migration, and colony formation in vitro as well as increased tumorigenesis in vivo, which could be reversed by targeted inhibition of the TAZ/YAP1 complex with verteporfin. Finally, xenografts expressing WWTR1 S89W displayed a shift in tumor phenotype, becoming more infiltrative as well as less differentiated, and were found to be composed of cells with conspicuous cytoplasmic clearing as compared to controls. Our results demonstrate that Hippo pathway alterations are likely drivers of cCCCs and likely contribute to the clear cell phenotype. Therapies targeting this pathway may constitute a new class of treatment for these rare, aggressive tumors. © 2022 The Pathological Society of Great Britain and Ireland.