Cardio-oncology care in the era of the coronavirus disease 2019 (COVID-19) pandemic: An International Cardio-Oncology Society (ICOS) statement.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has given rise to a pandemic of unprecedented proportions in the modern era because of its highly contagious nature and impact on human health and society: coronavirus disease 2019 (COVID-19). Patients with cardiovascular (CV) risk factors and established CV disease (CVD) are among those initially identified at the highest risk for serious complications, including death. Subsequent studies have pointed out that patients with cancer are also at high risk for a critical disease course. Therefore, the most vulnerable patients are seemingly those with both cancer and CVD, and a careful, unified approach in the evaluation and management of this patient population is especially needed in times of the COVID-19 pandemic. This review provides an overview of the unique implications of the viral outbreak for the field of cardio-oncology and outlines key modifications in the approach to this ever-increasing patient population. These modifications include a shift toward greater utilization of cardiac biomarkers and a more focused CV imaging approach in the broader context of modifications to typical practice pathways. The goal of this strategic adjustment is to minimize the risk of SARS-CoV-2 infection (or other future viral outbreaks) while not becoming negligent of CVD and its important impact on the overall outcomes of patients who are being treated for cancer.

High-throughput antibody screening from complex matrices using intact protein electrospray mass spectrometry.

Toward the goal of increasing the throughput of high-resolution mass characterization of intact antibodies, we developed a RapidFire-mass spectrometry (MS) assay using electrospray ionization. We achieved unprecedented screening throughput as fast as 15 s/sample, which is an order of magnitude improvement over conventional liquid chromatography (LC)-MS approaches. The screening enabled intact mass determination as accurate as 7 ppm with baseline resolution at the glycoform level for intact antibodies. We utilized this assay to characterize and perform relative quantitation of antibody species from 248 samples of 62 different cell line clones at four time points in 2 h using RapidFire-time-of-flight MS screening. The screening enabled selection of clones with the highest purity of bispecific antibody production and the results significantly correlated with conventional LC-MS results. In addition, analyzing antibodies from a complex plasma sample using affinity-RapidFire-MS was also demonstrated and qualified. In summary, the platform affords high-throughput analyses of antibodies, including bispecific antibodies and potential mispaired side products, in cell culture media, or other complex matrices.

Defining cardiovascular toxicities of cancer therapies: an International Cardio-Oncology Society (IC-OS) consensus statement.

The discipline of Cardio-Oncology has seen tremendous growth over the past decade. It is devoted to the cardiovascular (CV) care of the cancer patient, especially to the mitigation and management of CV complications or toxicities of cancer therapies, which can have profound implications on prognosis. To that effect, many studies have assessed CV toxicities in patients undergoing various types of cancer therapies; however, direct comparisons have proven difficult due to lack of uniformity in CV toxicity endpoints. Similarly, in clinical practice, there can be substantial differences in the understanding of what constitutes CV toxicity, which can lead to significant variation in patient management and outcomes. This document addresses these issues and provides consensus definitions for the most commonly reported CV toxicities, including cardiomyopathy/heart failure and myocarditis, vascular toxicity, and hypertension, as well as arrhythmias and QTc prolongation. The current document reflects a harmonizing review of the current landscape in CV toxicities and the definitions used to define these. This consensus effort aims to provide a structure for definitions of CV toxicity in the clinic and for future research. It will be important to link the definitions outlined herein to outcomes in clinical practice and CV endpoints in clinical trials. It should facilitate communication across various disciplines to improve clinical outcomes for cancer patients with CV diseases.

Detailed phenotyping reveals distinct trajectories of cardiovascular function and symptoms with exposure to modern breast cancer therapy.

BACKGROUND: Breast cancer therapies are associated with a risk of cardiac dysfunction, most commonly defined by changes in left ventricular ejection fraction (LVEF). Recently, the authors identified 3 classes of LVEF change after exposure to anthracyclines and/or trastuzumab using latent class growth modeling. The objective of the current study was to characterize the clinical, biochemical, and functional profiles associated with LVEF trajectory class membership. METHODS: Transthoracic echocardiography and biomarker assessments were performed and questionnaires were administered at standardized intervals in a longitudinal cohort of 314 patients with breast cancer who were treated with anthracyclines and/or trastuzumab. Univariable and multivariable multinomial regression analyses evaluated associations between baseline variables and LVEF trajectory class membership. Generalized estimating equations were used to define mean changes in cardiovascular measures over time within each class. RESULTS: Among the 3 distinct subgroups of LVEF changes identified (stable [class 1]; modest, persistent decline [class 2]; and significant early decline followed by partial recovery [class 3]), higher baseline LVEF, radiotherapy, and sequential therapy with anthracyclines and/or trastuzumab were associated with class 2 or 3 membership. Sustained abnormalities in longitudinal strain and N-terminal pro-B-type natriuretic peptide (NT-proBNP) were observed in patients in class 2, as were heart failure symptoms. Similar abnormalities were observed in patients in class 3, but there was a trend toward recovery, particularly for longitudinal strain. CONCLUSIONS: Patients with modest, persistent LVEF declines experienced sustained abnormalities in imaging and biochemical markers of cardiac function and heart failure symptoms. Further investigation is needed to characterize the long-term risk of heart failure, particularly in those with modest LVEF declines.

A 2D LC-MS/MS Strategy for Reliable Detection of 10-ppm Level Residual Host Cell Proteins in Therapeutic Antibodies.

Methodologies employing LC-MS/MS have been increasingly used for characterization and identification of residual host cell proteins (HCPs) in biopharmaceutical products to ensure their consistent product quality and safety for patients. To improve the sensitivity and reliability for HCP detection, we developed a high pH-low pH two-dimensional reversed phase LC-MS/MS approach in conjunction with offline fraction concatenation. Proof-of -concept was established using a model in which seven proteins spanning a size range of 29-78 kDa are spiked into a purified antibody product to simulate the presence of low-level HCPs. By incorporating a tandem column configuration and a shallow gradient through the second-dimension, all seven proteins were consistently identified at 10 ppm with 100% success rate following LC-MS/MS analysis of six concatenated fractions across multiple analysts, column lots and injection loads. Using the more complex Universal Proteomic Standard 1 (UPS-1) as an HCP model, positive identification was consistently achieved for 19 of the 22 proteins in 8-12 ppm range (10 ppm ±20%). For the first time, we demonstrate an effective LC-MS/MS strategy that not only has high sensitivity but also high reliability for HCP detection. The method performance has high impact on pharmaceutical company practices in using advanced LC-MS/MS technology to ensure product quality and patient safety.

How to Develop a Cardio-oncology Fellowship.

Management of cardiovascular disease in patients with cancer and cancer survivors requires particular clinical expertise and skills that are central to cardio-oncology. The areas of knowledge required include specific cardiovascular complications directly related to oncologic therapies and the impact of cancer and its therapies on existing or potential cardiovascular comorbidities. Many cancer therapeutics have potential cardiotoxicity. The conversion of many cancers to chronic conditions, rather than fatal diseases, has produced a population of patients with cancer at high risk for cardiovascular diseases that require specialized knowledge of treating physicians. Thus, there is a compelling need for enhanced cardio-oncology training.

Cardio-Oncology Training: A Proposal From the International Cardioncology Society and Canadian Cardiac Oncology Network for a New Multidisciplinary Specialty.

There is an increasing awareness and clinical interest in cardiac safety during cancer therapy as well as in optimally addressing cardiac issues in cancer survivors. Although there is an emerging expertise in this area, known as cardio-oncology, there is a lack of organization in the essential components of contemporary training. This proposal, an international consensus statement organized by the International Cardioncology Society and the Canadian Cardiac Oncology Network, attempts to marshal the important ongoing efforts for training the next generation of cardio-oncologists. The necessary elements are outlined, including the expectations for exposure necessary to develop adequate training. There should also be a commitment to local, regional, and international education and research in cardio-oncology as a requirement for advancement in the field.

Adult cancer survivorship: evolution, research, and planning care.

Increases in the number of adult cancer survivors and other issues have forced the oncology community to examine, evaluate, and alter the cancer care paradigm. Pediatric oncologists are grappling with the task of transitioning a growing population of adult survivors of childhood cancer to adult medicine, while oncologists caring for adult cancer survivors are seeking models of follow-up care that are acceptable to patients and providers. Workforce and access-to-care issues suggest that primary care providers will see more cancer survivors in their practices across time, although it is unclear how prepared they are for this task. Translational research is needed to develop evidence-based clinical care and survivorship care plans. A broad picture of the evolving field of adult cancer survivorship is presented. The recent focus on young adult survivors of childhood cancer, an overview of translational research needed to inform the physical and psychosocial care of cancer survivors, and the roles of primary and specialty care providers managing this population is examined. Finally, an overview of evolving treatment summary and care plan initiatives is presented.

Longitudinal Changes in Multiple Biomarkers Are Associated with Cardiotoxicity in Breast Cancer Patients Treated with Doxorubicin, Taxanes, and Trastuzumab.

BACKGROUND: Biomarkers may play an important role in identifying patients at risk for cancer therapy cardiotoxicity. Our objectives were to define the patterns of change in biomarkers with cancer therapy and their associations with cardiotoxicity. METHODS: In a multicenter cohort of 78 breast cancer patients undergoing doxorubicin and trastuzumab therapy, 8 biomarkers were evaluated at baseline and every 3 months over a maximum follow-up of 15 months. These biomarkers, hypothesized to be mechanistically relevant to cardiotoxicity, included high-sensitivity cardiac troponin I (hs-cTnI), high-sensitivity C-reactive protein (hsCRP), N-terminal pro-B-type natriuretic peptide (NT-proBNP), growth differentiation factor 15 (GDF-15), myeloperoxidase (MPO), placental growth factor (PlGF), soluble fms-like tyrosine kinase receptor-1 (sFlt-1), and galectin 3 (gal-3). We determined if biomarker increases were associated with cardiotoxicity at the same visit and the subsequent visit over the entire course of therapy. Cardiotoxicity was defined by the Cardiac Review and Evaluation Criteria; alternative definitions were also considered. RESULTS: Across the entire cohort, all biomarkers except NT-proBNP and gal-3 demonstrated increases by 3 months; these increases persisted for GDF-15, PlGF, and hs-cTnI at 15 months. Increases in MPO, PlGF, and GDF-15 were associated with cardiotoxicity at the same visit [MPO hazard ratio 1.38 (95% CI 1.10-1.71), P = 0.02; PlGF 3.78 (1.30-11.0), P = 0.047; GDF-15 1.71 (1.15-2.55), P = 0.01] and the subsequent visit. MPO was robust to alternative outcome definitions. CONCLUSIONS: Increases in MPO are associated with cardiotoxicity over the entire course of doxorubicin and trastuzumab therapy. Assessment with PlGF and GDF-15 may also be of value. These findings motivate validation studies in additional cohorts.

Patterns of cardiac toxicity associated with irreversible proteasome inhibition in the treatment of multiple myeloma.

Carfilzomib is a novel irreversible proteasome inhibitor (PI) used with increasing frequency to treat patients with relapsed and/or refractory multiple myeloma (RRMM). This agent is an effective treatment for this challenging population, but proteasome inhibition has the potential of significant cardiac toxicity via the accumulation of intracellular protein aggregates. Although large clinical trials have not suggested an excess of heart failure with PI therapy, nonhuman animal studies and case reports in humans with the PI bortezomib have suggested otherwise. We describe the clinical presentation and management of 6 patients with RRMM who experienced significant cardiac toxicity associated with carfilzomib treatment. A common clinical syndrome of dyspnea associated with left ventricular systolic and/or diastolic dysfunction was identified. These abnormalities were largely reversible with prompt cessation of PI therapy and initiation of traditional heart failure treatments. Safe readministration of carfilzomib with dose modification was possible in some cases.

Impact of Atrial Fibrillation on Heart Failure in Patients Treated With Anthracycline Chemotherapy.

Atrial fibrillation (AF) and anthracyclines are known risk factors for heart failure (HF). The magnitude of the effect of preexisting AF (preanthracycline AF) and newly developed AF (postanthracycline AF) in patients treated with anthracyclines on the occurrence of HF is unknown. The aim of our study was to characterize the impact of preanthracycline and postanthracycline AF on the subsequent occurrence of HF in patients treated with anthracyclines. In 5,598 patients treated with new anthracycline therapy at a tertiary center between 2008 and 2021, propensity score matching was used to match 204 pairs with or without preanthracycline AF and 135 pairs with or without postanthracycline AF. The primary outcome was new-onset symptomatic HF defined by the American Heart Association/American College of Cardiology guidelines. Patients with and without preanthracycline and postanthracycline AF were well matched for age, gender, medications, and cardiovascular risk factors. A total of 45 patients with preanthracycline AF and 23 matched patients developed HF (5-year cumulative incidence: 29% in the preanthracycline AF group and 13% in the matched group, p = 0.003; hazard ratio 2.1, 95% confidence interval 1.3 to 3.4, p = 0.004). A total of 161 patients (2.9%) developed postanthracycline AF. A total of 39 patients (5-year cumulative incidence: 40%) with postanthracycline AF and 9 matched patients (5-year cumulative incidence: 7%) developed HF (hazard ratio 6.1, 95% confidence interval 3.0 to 12.4, p <0.001). Preanthracycline AF and postanthracycline AF are associated with a high incidence of subsequent HF in patients treated with anthracyclines. Prospective studies of therapies are required to decrease HF in these high-risk patients.

Symptomatic Heart Failure and Clonal Hematopoiesis-Related Mutations in Patients With Acute Myeloid Leukemia.

Clonal hematopoiesis of indeterminate potential (CHIP) is a common risk factor for hematologic malignancies and cardiovascular diseases. This study aimed to investigate the association between CHIP-related mutations and symptomatic heart failure (HF) in patients diagnosed with acute myeloid leukemia (AML). A total of 563 patients with newly diagnosed AML who underwent DNA sequencing of bone marrow before treatment were retrospectively investigated. Cox proportional hazard regression models and Fine and Gray's subdistribution hazard regression models were used to assess the association between CHIP-related mutations and symptomatic HF. A total of 79.0% patients had at least 1 CHIP-related mutation; the most frequent mutations were DNMT3A, ASXL1, and TET2. A total of 51 patients (9.1%) developed symptomatic HF. The incidence of symptomatic HF was more frequent in patients with DNMT3A mutations (p <0.01), with a 1-year cumulative incidence of symptomatic HF in patients with DNMT3A mutations of 11.4%, compared with 3.9% in patients with wild-type DNMT3A (p <0.01). After adjustment for age and anthracyclines dose, DNMT3A mutations remained independently correlated with HF (hazard ratio 2.32, 95% confidence interval 1.26 to 4.29, p = 0.01). In conclusion, in patients with AML, the presence of DNMT3A mutations was associated with a twofold increased risk for symptomatic HF, irrespective of age and anthracyclines use.

Developing a Clinical Cardio-Oncology Program and the Building Blocks for Success: JACC: CardioOncology How To.

•Cardio-oncology programs are necessary to provide optimal cardiovascular care to cancer patients and survivors.•Focus on developing a clear vision and mission-successful programs must be tailored to an organization's unique landscape.•Fostering partnerships with cardiologists and oncologists to provide high-quality patient-centered care is crucial.•Patience is essential-program development takes time, but success can be achieved.

Combining regulated and constitutive protein expression significantly boosts protein expression by increasing productivity without affecting CHO cell growth.

Chinese hamster ovary (CHO) cells are commonly used for the expression of therapeutic proteins. To increase the titer output of CHO production cultures either specific productivity (Qp), growth, or both need to be increased. Generally, Qp and growth are inversely correlated and cell lines with high Qp have slower growth and vice versa. During the cell line development (CLD) process, the faster-growing cells tend to take over the culture and represent the majority of the isolated clones post single cell cloning. In this study, combinations of regulated and constitutive expression systems were used to supertransfect targeted integration (TI) cell lines expressing the same antibody either constitutively or under-regulated expression. Clone screening with a hybrid expression system (inducible + constitutive) allowed identification and selection of higher titer clones under uninduced conditions, without a negative impact on cell growth during clone selection and expansion. Induction of the regulated promoter(s) during the production phase increased the Qp without negatively affecting growth, resulting in approximately twofold higher titers (from 3.5 to 6-7 g/L). This was also confirmed using a 2-site TI host where the gene of interest was expressed inducibly from Site 1 and constitutively from Site 2. Our findings suggest that such a hybrid expression CLD system can be used to increase production titers, providing a novel approach for expression of therapeutic proteins with high titer market demands.

The Association of Metformin With Heart Failure in Patients With Diabetes Mellitus Receiving Anthracycline Chemotherapy.

Background: The prevention of heart failure (HF) is an important issue in patients treated with anthracyclines. Metformin, widely used to treat diabetes mellitus (DM), protects from anthracycline-induced cardiotoxicity in vitro and in animal models. Objectives: The aim of our study was to test the association of metformin with the occurrence of symptomatic HF in patients with DM receiving anthracyclines. Methods: A total of 561 patients with DM received new anthracycline therapy between 2008 and 2021 in a tertiary care center; propensity score matching was used to compare patients with or without metformin treatment. The primary outcome was new onset symptomatic HF occurring within 1 year of the initiation of anthracyclines. Results: A total of 315 patients (65 ± 11 years of age, 33.7% male) were included. Patients with and without metformin were well matched for age, sex, type of cancer, medications, and cardiovascular risk factors. Six patients treated with metformin and 17 matched patients developed HF within 1 year of anthracycline initiation. The incidence of HF in patients treated with metformin was lower than patients without metformin within 1 year after anthracyclines (cumulative incidence: 3.6% vs 10.5%; P = 0.022; HR: 0.35; 95% CI: 0.14-0.90; P = 0.029). The use of metformin (HR: 0.71; 95% CI: 0.50-1.00; P = 0.049), was also associated with lower mortality. Conclusions: The use of metformin was associated with a lower incidence of HF and overall mortality in patients with DM receiving anthracyclines. Our findings should be further confirmed by randomized control trials.

Adverse Cardiovascular Events Associated With Cyclin-Dependent Kinase 4/6 Inhibitors in Patients With Metastatic Breast Cancer.

Background Cyclin-dependent kinase (CDK) 4 and 6 inhibitors have significantly improved survival in patients with hormone receptor-positive metastatic breast cancer. There are few data regarding the epidemiology of cardiovascular adverse events (CVAEs) with these therapies. Methods and Results Using the OneFlorida Data Trust, adult patients without prior cardiovascular disease who received at least 1 CDK4/6 inhibitor were included in the analysis. CVAEs identified from International Classification of Diseases, Ninth and Tenth Revisions (ICD-9/10) codes included hypertension, atrial fibrillation(AF)/atrial flutter (AFL), heart failure/cardiomyopathy, ischemic heart disease, and pericardial disease. Competing risk analysis (Fine-Gray model) was used to determine the association between CDK4/6 inhibitor therapy and incident CVAEs. The effect of CVAEs on all-cause death was studied using Cox proportional hazard models. Propensity-weight analyses were performed to compare these patients to a cohort of patients treated with anthracyclines. A total of 1376 patients treated with CDK4/6 inhibitors were included in the analysis. CVAEs occurred in 24% (35.9 per 100 person-years). CVAEs were slightly higher in patients who received CKD4/6 inhibitors compared with anthracyclines (P=0.063), with higher death rate associated with the development of AF/AFL or cardiomyopathy/heart failure in the CDK4/6 group. The development of cardiomyopathy/heart failure and AF/AFL was associated with increased all-cause death (adjusted hazard ratio [HR], 4.89 [95% CI, 2.98-8.05]; and 5.88 [95% CI, 3.56-9.73], respectively). Conclusions CVAEs may be more common with CDK4/6 inhibitors than previously recognized, with increased death rates in these patients who develop AF/AFL or heart failure. Further research is needed to definitively determine cardiovascular risk associated with these novel anticancer treatments.

Incidence of MACE in Patients Treated With CAR-T Cell Therapy: A Prospective Study.

Background: Previous retrospective studies have shown that chimeric antigen receptor T (CAR-T) cell therapy may be associated with major adverse cardiovascular events (MACE), especially in the context of cytokine-release syndrome (CRS) events. Objectives: The aim of this prospective observational study was to define the occurrence of MACE in adults undergoing treatment with CAR-T cell therapy and identify associated risk factors. Methods: Vital signs, blood samples, and an echocardiogram were collected prior to and 2 days, 1 week, 1 month, and 6 months after CAR-T cell infusion, and charts were consulted at 12 months. In the event of CRS, echocardiography was repeated within 72 hours. MACE were defined as cardiovascular death, symptomatic heart failure, acute coronary syndrome, ischemic stroke, and de novo cardiac arrhythmia. Results: A total of 44 patients were enrolled (mean age 58 ± 11 years, 77% men). The median follow-up duration was 487 days (Q1-Q3: 258-622 days). There were 24 episodes of CRS in 23 patients (52%) (13 grade 1, 10 grade 2, and 1 grade 3), with a median time to CRS of 4 days. Two patients had MACE (heart failure with preserved ejection fraction and atrial fibrillation) within 1 year and 6 and 7 days after CAR-T cell infusion. There was no change in left ventricular ejection fraction, but a modest decrease in global longitudinal strain was noted. Conclusions: There were few cardiac effects associated with contemporary CAR-T cell therapy. As MACE occurred after CRS episodes, aggressive treatment and close follow-up during CRS events are essential.

Prospective surveillance and management of cardiac toxicity and health in breast cancer survivors.

Breast cancer is commonly diagnosed in postmenopausal women, the majority of whom express 1 or more cardiovascular disease risk factors. Cardiovascular disease poses a significant competing risk for morbidity and mortality among nonmetastatic breast cancer survivors. Adjuvant systemic therapies may result in late-cardiac toxicity decades after treatment completion. The cumulative incidence of treatment-related cardiotoxic outcomes may be as high as 33% after some adjuvant breast cancer therapies. Breast cancer treatment-induced cardiotoxicity may manifest as cardiomyopathy, coronary ischemia, thromboembolism, arrhythmias and conduction abnormalities, and valvular and pericardial disease. Evidence indicates that preexisting cardiovascular conditions such as hypertension or left ventricular dysfunction may compound the adverse effects of cardiotoxic treatments. There are currently no published clinical practice guidelines that address ongoing cardiac surveillance for cardiotoxicity after breast cancer, and existing guidelines for monitoring and promoting cardiovascular health in older women are often not followed. The multidisciplinary prospective surveillance system proposed elsewhere in this supplement would allow for earlier detection of cardiotoxicity from treatment and may improve monitoring of cardiovascular health in the growing population of breast cancer survivors.

A ribonucleoprotein-based decaplex CRISPR/Cas9 knockout strategy for CHO host engineering.

Chinese hamster ovary (CHO) cell engineering based on CRISPR/Cas9 knockout (KO) technology requires the delivery of guide RNA (gRNA) and Cas9 enzyme for efficient gene targeting. With an ever-increasing list of promising gene targets, developing, and optimizing a multiplex gene KO protocol is crucial for rapid CHO cell engineering. Here, we describe a method that can support efficient targeting and KO of up to 10 genes through sequential transfections. This method utilizes Cas9 protein to first screen multiple synthetic gRNAs per gene, followed by Sanger sequencing indel analysis, to identify effective gRNA sequences. Using sequential transfections of these potent gRNAs led to the isolation of single cell clones with the targeted deletion of all 10 genes (as confirmed by Sanger sequencing at the DNA level and mass spectrometry at the protein level). Screening 704 single cell clones yielded 6 clones in which all 10 genes were deleted through sequential transfections, demonstrating the success of this decaplex gene editing strategy. This pragmatic approach substantially reduces the time and effort required to generate multiple gene knockouts in CHO cells.

Paraoxonase-1 Activity in Breast Cancer Patients Treated With Doxorubicin With or Without Trastuzumab.

The objective of this study was to determine associations of paraoxonase-1 (PON-1) with development of cancer therapy-related cardiac dysfunction (CTRCD). PON-1 is a cardioprotective enzyme associated with high-density lipoprotein that prevents oxidized low-density lipoprotein formation. Given the role of oxidative stress in doxorubicin-induced cardiotoxicity, PON-1 activity may have relevance for the prediction of CTRCD. In 225 patients with breast cancer receiving doxorubicin with or without trastuzumab, we quantified PON-1 activity through its paraoxonase (Pon) and arylesterase (Aryl) enzymatic activity at baseline, during, and after doxorubicin completion. Echocardiograms were performed at baseline, during therapy, and annually. CTRCD was defined as a decrease in left ventricular ejection fraction by ≥10% from baseline to <50%. Associations between baseline biomarkers and clinical variables were determined using multivariable linear regression. Associations between changes in biomarker activity and time to CTRCD were evaluated using Cox regression. Pon was directly associated with Black race and inversely associated with Stage 2 cancer. Aryl was inversely associated with body mass index. After doxorubicin completion, activity levels of Pon and Aryl were significantly decreased (median ratio compared with baseline for Pon: 0.95 [Q1-Q3: 0.81-1.07, P < 0.001]; for Aryl: 0.97 [Q1-Q3: 0.85-1.08, P = 0.010]). A total of 184 patients had an available quantitated echocardiogram at baseline and at least 1 follow-up visit. Increases from baseline in Pon at doxorubicin completion were independently associated with increased CTRCD risk (per 10% increase: hazard ratio [HR]: 1.21; 95% confidence interval [CI]: 1.05-1.39; P = 0.007). Associations between increases in Aryl and CTRCD tended in the same direction but were of borderline statistical significance (HR: 1.17; 95% CI: 0.99-1.38; P = 0.071). In patients with breast cancer treated with doxorubicin with or without trastuzumab, increases in the Pon enzymatic activity level of PON-1 were associated with increased CTRCD risk. PON-1 activity may be relevant to mechanistic risk prediction of cardiotoxicity with anthracyclines.