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Purpose The therascreen PIK3CA mutation assay and the alpha-specific PI3K inhibitor alpelisib are FDA-approved for identifying and treating patients with advanced PIK3CA- mutated ( PIK3CA mut) breast cancer (BC). However, it is currently unknown to what extend this assay detects most PIK3CA mutations in BC. This information is critical as patients and clinicians are using this and other genomic assays to indicate alpelisib. Methods Data from 6338 patients with BC was explored across 10 publicly available studies. The primary objective was to evaluate the proportion and distribution of PIK3CA mutations in BC. Secondary objectives were (1) to evaluate in silico the spectrum of PIK3CA mutations in BC that would be captured by the therascreen panel; (2) to evaluate the proportion and distribution of PIK3CA mutations in hormone receptor-positive/HER2-negative (HR+/HER2−), HER2+, and triple-negative BC (TNBC); and (3) to explore the identification of PIK3CA mutations in a cohort of 48 HR+/HER2− advanced BC patients by the Guardant B360 circulating tumor DNA (ctDNA) assay. Results Patients with PIK3CA mut tumors represented 35.7% (2261/6338). Five PIK3CA mutations comprised 73% of all PIK3CA mutations: H1047R (35%), E545K (17%), E542K (11%), N345K (6%), and H1047L (4%). Therascreen gene list would capture 72% of all PIK3CA mutations and 80% of patients with a known PIK3CA mut BC. Among patients with double PIK3CA mut tumors (12% of all PIK3CA mut), the therascreen panel would capture 78% as harboring 1 single PIK3CA mutation, 17% as PIK3CA mut undetected, and 5% as PIK3CA double-mut. PIK3CA mutation rates were lower in TNBC (16%) compared to HR+/HER2 (42%) and HER2+ (31%) BC; however, the distribution of the 4 main PIK3CA mutations across subtypes was similar. Finally, 28% of PIK3CA mutations identified in ctDNA in 48 patients with advanced HR+/HER2− BC were not part of the therascreen panel. Conclusion PIK3CA mutations in BC are heterogenous and ~ 20% of patients with a known PIK3CA mutation, and 95% with a known double PIK3CA mut tumor, would not be captured by the therascreen panel. Finally, the clinical utility of PIK3CA mutations not present in the therascreen companion diagnostic assay or identified by other sequencing-based assays needs further investigation.

The HER2-enriched (HER2-E) subtype within HER2-positive (HER2+) breast cancer is highly addicted to the HER2 pathway. However, ∼20–60% of HER2+/HER2-E tumors do not achieve a complete response following anti-HER2 therapies. Here we evaluate gene expression data before, during and after neoadjuvant treatment with lapatinib and trastuzumab in HER2+/HER2-E tumors of the PAMELA trial and breast cancer cell lines. Our results reveal that dual HER2 blockade in HER2-E disease induces a low-proliferative Luminal A phenotype both in patient’s tumors and in vitro models. These biological changes are more evident in hormone receptor-positive (HR+) disease compared to HR-negative disease. Interestingly, increasing the luminal phenotype with anti-HER2 therapy increased sensitivity to CDK4/6 inhibition. Finally, discontinuation of HER2-targeted therapy in vitro, or acquired resistance to anti-HER2 therapy, leads to restoration of the original HER2-E phenotype. Our findings support the use of maintenance anti-HER2 therapy and the therapeutic exploitation of subtype switching with CDK4/6 inhibition. HER2-enriched breast cancers within the HER2-positive subtype are addicted to the HER2 pathway. Here, the authors analyse gene expression before, during, and after treatment with anti-HER2-based therapies in the phase II PAMELA clinical trial, finding phenotypic changes induced by treatment.

Immune checkpoint inhibitors have modified the treatment algorithm in a variety of cancer types, including breast cancer. Nevertheless, optimal selection of ideal candidates to these drugs remains an unmet need. Although PD-L1 expression by immunohistochemistry seems to be the most promising biomarker to date, its predictive ability is far from ideal. Thus, the development of new predictive biomarkers is essential for a better selection of patients. Here, we discuss potential biomarkers beyond PD-L1 that could play an important role in precision cancer immunotherapy.

Chimeric antigen receptor (CAR)-T cell therapy for solid tumors faces significant hurdles, including T-cell inhibition mediated by the PD-1/PD-L1 axis. The effects of disrupting this pathway on T-cells are being actively explored and controversial outcomes have been reported. Here, we hypothesize that CAR-antigen affinity may be a key factor modulating T-cell susceptibility towards the PD-1/PD-L1 axis. We systematically interrogate CAR-T cells targeting HER2 with either low (LA) or high affinity (HA) in various preclinical models. Our results reveal an increased sensitivity of LA CAR-T cells to PD-L1-mediated inhibition when compared to their HA counterparts by using in vitro models of tumor cell lines and supported lipid bilayers modified to display varying PD-L1 densities. CRISPR/Cas9-mediated knockout (KO) of PD-1 enhances LA CAR-T cell cytokine secretion and polyfunctionality in vitro and antitumor effect in vivo and results in the downregulation of gene signatures related to T-cell exhaustion. By contrast, HA CAR-T cell features remain unaffected following PD-1 KO. This behavior holds true for CD28 and ICOS but not 4-1BB co-stimulated CAR-T cells, which are less sensitive to PD-L1 inhibition albeit targeting the antigen with LA. Our findings may inform CAR-T therapies involving disruption of PD-1/PD-L1 pathway tailored in particular for effective treatment of solid tumors. It has been suggested that targeting the PD-1/PD-L1 axis can increase the anti-tumor properties of chimeric antigen receptor (CAR)-T cells. Here the authors report that CAR affinity modulates the sensitivity of CAR-T cells to PD-1/PD-L1-mediated inhibition.

In advanced breast cancer, biomarker identification and patient selection using a metastatic tumor biopsy is becoming more necessary. However, the biology of metastasis according to the organ site is largely unknown. Here, we evaluated the expression of 771 genes in 184 metastatic samples across 11 organs, including liver, lung, brain, and bone, and made the following observations. First, all PAM50 molecular intrinsic subtypes were represented across organs and within immunohistochemistry‐based groups. Second, HER2‐low disease was identified across all organ sites, including bone, and HER2 expression significantly correlated with ERBB2 expression. Third, the majority of expression variation was explained by intrinsic subtype and not organ of metastasis. Fourth, subtypes and individual subtype‐related genes/signatures were significantly associated with overall survival. Fifth, we identified 74 genes whose expression was organ‐specific and subtype‐independent. Finally, immune profiles were found more expressed in lung compared to brain or liver metastasis. Our results suggest that relevant tumor biology can be captured in metastatic tissues across a variety of organ sites; however, unique biological features according to organ site were also identified and future studies should explore their implications in diagnostic and therapeutic interventions. We evaluated gene expression in 184 metastatic breast cancer samples across 11 organs. All PAM50 subtypes were represented across metastatic sites and associated with survival. HER2‐low disease was identified across sites. Immune gene expression was higher in lung than brain or liver metastasis. Relevant tumor biology can be captured in metastatic tissue, while each site shows unique biological features.

In early-stage HER2-positive breast cancer, escalation or de-escalation of systemic therapy is a controversial topic. As an aid to treatment decisions, we aimed to develop a prognostic assay that integrates multiple data types for predicting survival outcome in patients with newly diagnosed HER2-positive breast cancer. We derived a combined prognostic model using retrospective clinical–pathological data on stromal tumour-infiltrating lymphocytes, PAM50 subtypes, and expression of 55 genes obtained from patients who participated in the Short-HER phase 3 trial. The trial enrolled patients with newly diagnosed, node-positive, HER2-positive breast cancer or, if node negative, with at least one risk factor (ie, tumour size >2 cm, histological grade 3, lymphovascular invasion, Ki67 >20%, age ≤35 years, or hormone receptor negativity), and randomly assigned them to adjuvant anthracycline plus taxane-based combinations with either 9 weeks or 1 year of trastuzumab. Trastuzumab was administered intravenously every 3 weeks (8 mg/kg loading dose at first cycle, and 6 mg/kg thereafter) for 18 doses or weekly (4 mg/kg loading dose in the first week, and 2 mg/kg thereafter) for 9 weeks, starting concomitantly with the first taxane dose. Median follow-up was 91·4 months (IQR 75·1–105·6). The primary objective of our study was to derive and evaluate a combined prognostic score associated with distant metastasis-free survival (the time between randomisation and distant recurrence or death before recurrence), an exploratory endpoint in Short-HER. Patient samples in the training dataset were split into a training set (n=290) and a testing set (n=145), balancing for event and treatment group. The training set was further stratified into 100 iterations of Monte-Carlo cross validation (MCCV). Cox proportional hazard models were fit to MCCV training samples using Elastic-Net. A maximum of 92 features were assessed. The final prognostic model was evaluated in an independent combined dataset of 267 patients with early-stage HER2-positive breast cancer treated with different neoadjuvant and adjuvant anti-HER2-based combinations and from four other studies (PAMELA, CHER-LOB, Hospital Clinic, and Padova) with disease-free survival outcome data. From Short-HER, data from 435 (35%) of 1254 patients for tumour size (T1 vs rest), nodal status (N0 vs rest), number of tumour-infiltrating lymphocytes (continuous variable), subtype (HER2-enriched and basal-like vs rest), and 13 genes composed the final model (named HER2DX). HER2DX was significantly associated with distant metastasis-free survival as a continuous variable (p<0·0001). HER2DX median score for quartiles 1–2 was identified as the cutoff to identify low-risk patients; and the score that distinguished quartile 3 from quartile 4 was the cutoff to distinguish medium-risk and high-risk populations. The 5-year distant metastasis-free survival of the low-risk, medium-risk, and high-risk populations were 98·1% (95% CI 96·3–99·9), 88·9% (83·2–95·0), and 73·9% (66·0–82·7), respectively (low-risk vs high-risk hazard ratio [HR] 0·04, 95% CI 0·0–0·1, p<0·0001). In the evaluation cohort, HER2DX was significantly associated with disease-free survival as a continuous variable (HR 2·77, 95% CI 1·4–5·6, p=0·0040) and as group categories (low-risk vs high-risk HR 0·27, 0·1–0·7, p=0·005). 5-year disease-free survival in the HER2DX low-risk group was 93·5% (89·0–98·3%) and in the high-risk group was 81·1% (71·5–92·1). The HER2DX combined prognostic score identifies patients with early-stage, HER2-positive breast cancer who might be candidates for escalated or de-escalated systemic treatment. Future clinical validation of HER2DX seems warranted to establish its use in different scenarios, especially in the neoadjuvant setting. Instituto Salud Carlos III, Save the Mama, Pas a Pas, Fundación Científica, Asociación Española Contra el Cáncer, Fundación SEOM, National Institutes of Health, Agenzia Italiana del Farmaco, International Agency for Research on Cancer, and the Veneto Institute of Oncology, and Italian Association for Cancer Research.

Anti-HER2 antibodies are effective but often lead to resistance in patients with HER2+ breast cancer. Here, we report an epigenetic crosstalk with aberrant glycerophospholipid metabolism and inflammation as a key resistance mechanism of anti-HER2 therapies in HER2+ breast cancer. Histone reader ZMYND8 specifically confers resistance to cancer cells against trastuzumab and/or pertuzumab. Mechanistically, ZMYND8 enhances cPLA2α expression in resistant tumor cells through inducing c-Myc. cPLA2α inactivates phosphatidylcholine-specific phospholipase C to inhibit phosphatidylcholine breakdown into diacylglycerol, which diminishes protein kinase C activity leading to interleukin-27 secretion. Supplementation with interleukin-27 protein counteracts cPLA2α loss to reinforce trastuzumab resistance in HER2+ tumor cells and patient-derived organoids. Upregulation of ZMYND8, c-Myc, cPLA2α, and IL-27 is prevalent in HER2+ breast cancer patients following HER2-targeted therapies. Targeting c-Myc or cPLA2α effectively overcomes anti-HER2 therapy resistance in patient-derived xenografts. Collectively, this study uncovers a druggable signaling cascade that drives resistance to HER2-targeted therapies in HER2+ breast cancer. While HER2-targeted therapies such as trastuzumab can be effective in patients with breast cancer, resistance often develops. Here, the authors demonstrate that the histone reader ZYMND8 promotes glycerophospholipid metabolic reprogramming via c-Myc and cPLA2α to increase secretion of IL-27, mediating resistance to HER2-targeted antibodies in preclinical models of breast cancer.

Older adults with HER2-positive early breast cancer are underrepresented in clinical trials, and the benefit of chemotherapy in this population remains uncertain. We evaluated the HER2DX genomic assay within the randomized RESPECT trial (NCT01104935), which compared adjuvant trastuzumab with or without chemotherapy in patients aged 70–80 years. In this prespecified translational analysis (Trans-RESPECT), HER2DX scores were available for 154 patients. The HER2DX risk score classified 74.0% as low risk and 26.0% as high risk. Ten-year relapse-free and overall survival were higher in the low-risk group. HER2DX remained independently associated with overall survival in multivariable analysis. The HER2DX immune, luminal, and proliferation signatures that compose the risk score were also prognostic. While the HER2DX pCR score was not prognostic overall, exploratory subgroup analyses suggested a potential survival benefit from chemotherapy in the pCR-high group. HER2DX offers prognostic value and may guide chemotherapy use in older patients with HER2-positive early breast cancer. Clinical Trial Information NCT01104935 In the RESPECT randomized trial (trastuzumab ± chemotherapy) in women aged 70–80 with HER2-positive early breast cancer, tumor/immune profiling with HER2DX stratified prognosis and helped identify when chemotherapy may be avoided.

Triple negative breast cancers (TNBCs) lack recurrent targetable driver mutations but demonstrate frequent copy number aberrations (CNAs). Here, we describe an integrative genomic and RNAi-based approach that identifies and validates gene addictions in TNBCs. CNAs and gene expression alterations are integrated and genes scored for pre-specified target features revealing 130 candidate genes. We test functional dependence on each of these genes using RNAi in breast cancer and non-malignant cells, validating malignant cell selective dependence upon 37 of 130 genes. Further analysis reveals a cluster of 13 TNBC addiction genes frequently co-upregulated that includes genes regulating cell cycle checkpoints, DNA damage response, and malignant cell selective mitotic genes. We validate the mechanism of addiction to a potential drug target: the mitotic kinesin family member C1 (KIFC1/HSET), essential for successful bipolar division of centrosome-amplified malignant cells and develop a potential selection biomarker to identify patients with tumors exhibiting centrosome amplification. Triple negative breast cancers harbor multiple copy number aberrations driving gene expression changes thought to underpin their malignant phenotypes. Here the authors integrate these features, finding and functionally validating 37 gene addictions among which they identify the mechanism of addiction to KIFC1, a potential selective drug target.