Clinical impact of COVID-19 on patients with cancer (CCC19): a cohort study.

BACKGROUND: Data on patients with COVID-19 who have cancer are lacking. Here we characterise the outcomes of a cohort of patients with cancer and COVID-19 and identify potential prognostic factors for mortality and severe illness. METHODS: In this cohort study, we collected de-identified data on patients with active or previous malignancy, aged 18 years and older, with confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection from the USA, Canada, and Spain from the COVID-19 and Cancer Consortium (CCC19) database for whom baseline data were added between March 17 and April 16, 2020. We collected data on baseline clinical conditions, medications, cancer diagnosis and treatment, and COVID-19 disease course. The primary endpoint was all-cause mortality within 30 days of diagnosis of COVID-19. We assessed the association between the outcome and potential prognostic variables using logistic regression analyses, partially adjusted for age, sex, smoking status, and obesity. This study is registered with ClinicalTrials.gov, NCT04354701, and is ongoing. FINDINGS: Of 1035 records entered into the CCC19 database during the study period, 928 patients met inclusion criteria for our analysis. Median age was 66 years (IQR 57-76), 279 (30%) were aged 75 years or older, and 468 (50%) patients were male. The most prevalent malignancies were breast (191 [21%]) and prostate (152 [16%]). 366 (39%) patients were on active anticancer treatment, and 396 (43%) had active (measurable) cancer. At analysis (May 7, 2020), 121 (13%) patients had died. In logistic regression analysis, independent factors associated with increased 30-day mortality, after partial adjustment, were: increased age (per 10 years; partially adjusted odds ratio 1·84, 95% CI 1·53-2·21), male sex (1·63, 1·07-2·48), smoking status (former smoker vs never smoked: 1·60, 1·03-2·47), number of comorbidities (two vs none: 4·50, 1·33-15·28), Eastern Cooperative Oncology Group performance status of 2 or higher (status of 2 vs 0 or 1: 3·89, 2·11-7·18), active cancer (progressing vs remission: 5·20, 2·77-9·77), and receipt of azithromycin plus hydroxychloroquine (vs treatment with neither: 2·93, 1·79-4·79; confounding by indication cannot be excluded). Compared with residence in the US-Northeast, residence in Canada (0·24, 0·07-0·84) or the US-Midwest (0·50, 0·28-0·90) were associated with decreased 30-day all-cause mortality. Race and ethnicity, obesity status, cancer type, type of anticancer therapy, and recent surgery were not associated with mortality. INTERPRETATION: Among patients with cancer and COVID-19, 30-day all-cause mortality was high and associated with general risk factors and risk factors unique to patients with cancer. Longer follow-up is needed to better understand the effect of COVID-19 on outcomes in patients with cancer, including the ability to continue specific cancer treatments. FUNDING: American Cancer Society, National Institutes of Health, and Hope Foundation for Cancer Research.

Antibiotic use during cytarabine consolidation in acute myeloid leukemia.

Acute myeloid leukemia (AML) patients undergoing consolidation chemotherapy with intermediate or high-dose cytarabine (IDAC/HiDAC) are often placed on prophylactic antibacterials. This practice is largely based on the benefits of prophylaxis (PPX) during induction chemotherapy. However, recent concerns regarding antibacterial prophylaxis have emerged including risk of Clostridioides difficile colitis, medication toxicities, and the potential for fostering multidrug-resistant pathogens. We therefore retrospectively explored whether antibacterial PPX is beneficial during cytarabine consolidation. Adult AML patients who received IDAC/HiDAC at our institution from January 2007 to March 2018 were evaluated for receipt of antibacterial PPX. The primary endpoint was rate of febrile neutropenia (FN); secondary endpoints were rates of unplanned hospitalization, bacteremia, infection from resistant organisms, C. difficile colitis, and death from infection. One hundred twenty patients with data from 229 IDAC/HiDAC cycles were included. Patients who received antibacterial PPX were more often hospitalized during cytarabine cycle 1 (C1) than those who received no PPX. Patients who received PPX had significantly more episodes of bacteremia, in addition to infections from resistant, predominantly Gram-positive organisms during cycle 1 of consolidation than those without PPX. Antibacterial PPX during IDAC/HiDAC consolidation treatment at our institution did not decrease the rates of FN, hospitalization, or bacteremia and was associated with higher risk of infection from drug-resistant bacteria in C1. Prospective studies examining antibacterial prophylaxis during cytarabine consolidation for AML patients are necessary, with strong consideration made for institution-specific protocols.

Transfusion dependence, use of hospice services, and quality of end-of-life care in leukemia.

Hospice provides high-quality end-of-life care, but patients with leukemias use hospice services less frequently than those with solid tumors. Transfusion dependence (TD) may hinder or delay enrollment, because hospice organizations typically disallow transfusions. We examined the association between TD and end-of-life outcomes among Medicare beneficiaries with leukemia. From the Surveillance, Epidemiology, and End Results-Medicare database, we selected beneficiaries with acute and chronic leukemias who died in 2001-2011. We defined TD as ≥2 transfusions within 30 days before death or hospice enrollment. End points included hospice enrollment and length of stay, reporting relative risk (RR) adjusted for key covariates. Among 21 033 patients with a median age of 79 years, 20% were transfusion dependent before death/hospice enrollment. Use of hospice increased from 35% in 2001 to 49% in 2011. Median time on hospice was 9 days and was shorter for transfusion-dependent patients (6 vs 11 days; P < .001). Adjusting for baseline characteristics, TD was associated with a higher use of hospice services (RR, 1.08; 95% confidence interval [CI], 1.04-1.12) but also with 51% shorter hospice length of stay (RR, 0.49; 95% CI, 0.44-0.54). Hospice enrollees had a lower likelihood of inpatient death and chemotherapy use and lower median Medicare spending at end-of-life, regardless of TD status. In conclusion, relatively increased hospice use combined with a markedly shorter length of stay among transfusion-dependent patients suggests that they have a high and incompletely met need for hospice services and that they experience a barrier to timely referral. Policy solutions supporting palliative transfusions may maximize the benefits of hospice for leukemia patients.

Low dose 100 cGy irradiation as a potential therapy for pulmonary hypertension.

Pulmonary hypertension (PH) is an incurable disease characterized by pulmonary vascular remodeling and ultimately death. Two rodent models of PH include treatment with monocrotaline or exposure to a vascular endothelial growth factor receptor inhibitor and hypoxia. Studies in these models indicated that damaged lung cells evolve extracellular vesicles which induce production of progenitors that travel back to the lung and induce PH. A study in patients with pulmonary myelofibrosis and PH indicated that 100 cGy lung irradiation could remit both diseases. Previous studies indicated that murine progenitors were radiosensitive at very low doses, suggesting that 100 cGy treatment of mice with induced PH might be an effective PH therapy. Our hypothesis is that the elimination of the PH-inducing marrow cells by low dose irradiation would remove the cellular influences creating PH. Here we show that low dose whole-body irradiation can both prevent and reverse established PH in both rodent models of PH.

Predictors of high-intensity care at the end of life among older adults with solid tumors: A population-based study.

INTRODUCTION: High-intensity end-of-life (EoL) care can be burdensome for patients, caregivers, and health systems and does not confer any meaningful clinical benefit. Yet, there are significant knowledge gaps regarding the predictors of high-intensity EoL care. In this study, we identify risk factors associated with high-intensity EoL care among older adults with the four most common malignancies, including breast, prostate, lung, and colorectal cancer. MATERIALS AND METHODS: Using SEER-Medicare data, we conducted a retrospective analysis of Medicare beneficiaries aged 65 and older who died of breast, prostate, lung, or colorectal cancer between 2011 and 2015. We used multivariable logistic regression to identify clinical, demographic, socioeconomic, and geographic predictors of high-intensity EoL care, which we defined as death in an acute care hospital, receipt of any oral or parenteral chemotherapy within 14 days of death, one or more admissions to the intensive care unit within 30 days of death, two or more emergency department visits within 30 days of death, or two or more inpatient admissions within 30 days of death. RESULTS: Among 59,355 decedents, factors associated with increased likelihood of receiving high-intensity EoL care were increased comorbidity burden (odds ratio [OR]:1.29; 95% confidence interval [CI]:1.28-1.30), female sex (OR:1.05; 95% CI:1.01-1.09), Black race (OR:1.14; 95% CI:1.07-1.23), Other race/ethnicity (OR:1.20; 95% CI:1.10-1.30), stage III disease (OR:1.11; 95% CI:1.05-1.18), living in a county with >1,000,000 people (OR:1.23; 95% CI:1.16-1.31), living in a census tract with 10%-<20% poverty (OR:1.09; 95% CI:1.03-1.16) or 20%-100% poverty (OR:1.12; 95% CI:1.04-1.19), and having state-subsidized Medicare premiums (OR:1.18; 95% CI:1.12-1.24). The risk of high-intensity EoL care was lower among patients who were older (OR:0.98; 95% CI:0.98-0.99), lived in the Midwest (OR:0.69; 95% CI:0.65-0.75), South (OR:0.70; 95% CI:0.65-0.74), or West (OR:0.81; 95% CI:0.77-0.86), lived in mostly rural areas (OR:0.92; 95% CI:0.86-1.00), and had poor performance status (OR:0.26; 95% CI:0.25-0.28). Results were largely consistent across cancer types. DISCUSSION: The risk factors identified in our study can inform the development of new interventions for patients with cancer who are likely to receive high-intensity EoL care. Health systems should consider incorporating these risk factors into decision-support tools to assist clinicians in identifying which patients should be referred to hospice and palliative care.

The Importance of Recency of Cancer Diagnosis in Patients Hospitalized with COVID-19-Glimpses from an EHR-based Study.

Multiple prior studies have shown an increased risk of severe disease and death from SARS-CoV-2 infection in patients with cancer. Nolan and colleagues conducted a multi-institution, electronic health record (EHR)-based study of adults hospitalized with COVID-19 delineating the difference in outcomes when stratified by current versus former cancer diagnosis and found that only a current diagnosis appears to confer an increased risk of severe COVID-19 and death.We review these findings in the context of other studies examining outcomes for individuals with cancer diagnoses and COVID-19. We also address questions raised by this type of study about the significant challenges of EHR-based studies and discuss potential avenues for future research in this arena. See related article by Nolan et al., p. 12.

Systemic Anticancer Therapy and Thromboembolic Outcomes in Hospitalized Patients With Cancer and COVID-19.

Importance: Systematic data on the association between anticancer therapies and thromboembolic events (TEEs) in patients with COVID-19 are lacking. Objective: To assess the association between anticancer therapy exposure within 3 months prior to COVID-19 and TEEs following COVID-19 diagnosis in patients with cancer. Design, Setting, and Participants: This registry-based retrospective cohort study included patients who were hospitalized and had active cancer and laboratory-confirmed SARS-CoV-2 infection. Data were accrued from March 2020 to December 2021 and analyzed from December 2021 to October 2022. Exposure: Treatments of interest (TOIs) (endocrine therapy, vascular endothelial growth factor inhibitors/tyrosine kinase inhibitors [VEGFis/TKIs], immunomodulators [IMiDs], immune checkpoint inhibitors [ICIs], chemotherapy) vs reference (no systemic therapy) in 3 months prior to COVID-19. Main Outcomes and Measures: Main outcomes were (1) venous thromboembolism (VTE) and (2) arterial thromboembolism (ATE). Secondary outcome was severity of COVID-19 (rates of intensive care unit admission, mechanical ventilation, 30-day all-cause mortality following TEEs in TOI vs reference group) at 30-day follow-up. Results: Of 4988 hospitalized patients with cancer (median [IQR] age, 69 [59-78] years; 2608 [52%] male), 1869 had received 1 or more TOIs. Incidence of VTE was higher in all TOI groups: endocrine therapy, 7%; VEGFis/TKIs, 10%; IMiDs, 8%; ICIs, 12%; and chemotherapy, 10%, compared with patients not receiving systemic therapies (6%). In multivariable log-binomial regression analyses, relative risk of VTE (adjusted risk ratio [aRR], 1.33; 95% CI, 1.04-1.69) but not ATE (aRR, 0.81; 95% CI, 0.56-1.16) was significantly higher in those exposed to all TOIs pooled together vs those with no exposure. Among individual drugs, ICIs were significantly associated with VTE (aRR, 1.45; 95% CI, 1.01-2.07). Also noted were significant associations between VTE and active and progressing cancer (aRR, 1.43; 95% CI, 1.01-2.03), history of VTE (aRR, 3.10; 95% CI, 2.38-4.04), and high-risk site of cancer (aRR, 1.42; 95% CI, 1.14-1.75). Black patients had a higher risk of TEEs (aRR, 1.24; 95% CI, 1.03-1.50) than White patients. Patients with TEEs had high intensive care unit admission (46%) and mechanical ventilation (31%) rates. Relative risk of death in patients with TEEs was higher in those exposed to TOIs vs not (aRR, 1.12; 95% CI, 0.91-1.38) and was significantly associated with poor performance status (aRR, 1.77; 95% CI, 1.30-2.40) and active/progressing cancer (aRR, 1.55; 95% CI, 1.13-2.13). Conclusions and Relevance: In this cohort study, relative risk of developing VTE was high among patients receiving TOIs and varied by the type of therapy, underlying risk factors, and demographics, such as race and ethnicity. These findings highlight the need for close monitoring and perhaps personalized thromboprophylaxis to prevent morbidity and mortality associated with COVID-19-related thromboembolism in patients with cancer.

Coinfections in Patients With Cancer and COVID-19: A COVID-19 and Cancer Consortium (CCC19) Study.

BACKGROUND: The frequency of coinfections and their association with outcomes have not been adequately studied among patients with cancer and coronavirus disease 2019 (COVID-19), a high-risk group for coinfection. METHODS: We included adult (≥18 years) patients with active or prior hematologic or invasive solid malignancies and laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) infection, using data from the COVID-19 and Cancer Consortium (CCC19, NCT04354701). We captured coinfections within ±2 weeks from diagnosis of COVID-19, identified factors cross-sectionally associated with risk of coinfection, and quantified the association of coinfections with 30-day mortality. RESULTS: Among 8765 patients (hospitalized or not; median age, 65 years; 47.4% male), 16.6% developed coinfections: 12.1% bacterial, 2.1% viral, 0.9% fungal. An additional 6.4% only had clinical diagnosis of a coinfection. The adjusted risk of any coinfection was positively associated with age >50 years, male sex, cardiovascular, pulmonary, and renal comorbidities, diabetes, hematologic malignancy, multiple malignancies, Eastern Cooperative Oncology Group Performance Status, progressing cancer, recent cytotoxic chemotherapy, and baseline corticosteroids; the adjusted risk of superinfection was positively associated with tocilizumab administration. Among hospitalized patients, high neutrophil count and C-reactive protein were positively associated with bacterial coinfection risk, and high or low neutrophil count with fungal coinfection risk. Adjusted mortality rates were significantly higher among patients with bacterial (odds ratio [OR], 1.61; 95% CI, 1.33-1.95) and fungal (OR, 2.20; 95% CI, 1.28-3.76) coinfections. CONCLUSIONS: Viral and fungal coinfections are infrequent among patients with cancer and COVID-19, with the latter associated with very high mortality rates. Clinical and laboratory parameters can be used to guide early empiric antimicrobial therapy, which may improve clinical outcomes.

Early Palliative Care Services and End-of-Life Care in Medicare Beneficiaries with Hematologic Malignancies: A Population-Based Retrospective Cohort Study.

Background: Patients with hematologic malignancies (HM) often receive aggressive care at the end of life (EOL). Early palliative care (PC) has been shown to improve EOL care outcomes, but its benefits are less established in HM than in solid tumors. Objectives: We sought to describe the use of billed PC services among Medicare beneficiaries with HM. We hypothesized that receipt of early PC services (rendered >30 days before death) may be associated with less aggressive EOL care. Design: Retrospective cohort analysis Setting/Subjects: Using the Surveillance, Epidemiology, and End Results-Medicare registry, we studied patients with leukemia, lymphoma, myeloma, myelodysplastic syndrome, or myeloproliferative neoplasm who died between 2001 and 2015. Measurements: We described trends in the use of PC services and evaluated the association between early PC services and metrics of EOL care aggressiveness. Results: Among 139,191 decedents, the proportion receiving PC services increased from 0.4% in 2001 to 13.3% in 2015. Median time from first encounter to death was 10 days and 84.3% of encounters occurred during hospitalizations. In patients who survived >30 days from diagnosis (N = 120,741), the use of early PC services was more frequent in acute leukemia, women, and black patients, among other characteristics. Early PC services were associated with increased hospice use and decreased health care utilization at the EOL. Conclusion: Among patients with HM, there was an upward trend in PC services, and early PC services were associated with less aggressive EOL care. Our results support the need for prospective trials of early PC in HM.

Detection of clonotypic DNA in the cerebrospinal fluid as a marker of central nervous system invasion in lymphoma.

The diagnosis of parenchymal central nervous system (CNS) invasion and prediction of risk for future CNS recurrence are major challenges in the management of aggressive lymphomas, and accurate biomarkers are needed to supplement clinical risk predictors. For this purpose, we studied the results of a next-generation sequencing (NGS)-based assay that detects tumor-derived DNA for clonotypic immunoglobulin gene rearrangements in the cerebrospinal fluid (CSF) of patients with lymphomas. Used as a diagnostic tool, the NGS-minimal residual disease (NGS-MRD) assay detected clonotypic DNA in 100% of CSF samples from 13 patients with known CNS involvement. They included 7 patients with parenchymal brain disease only, whose CSF tested negative by standard cytology and flow cytometry, and 6 historical DNA aliquots collected from patients at a median of 39 months before accession, which had failed to show clonal rearrangements using standard polymerase chain reaction. For risk prognostication, we prospectively collected CSF from 22 patients with newly diagnosed B-cell lymphomas at high clinical risk of CNS recurrence, of whom 8 (36%) had detectable clonotypic DNA in the CSF. Despite intrathecal prophylaxis, a positive assay of CSF was associated with a 29% cumulative risk of CNS recurrence within 12 months of diagnosis, in contrast with a 0% risk among patients with negative CSF (P = .045). These observations suggest that detection of clonotypic DNA can aid in the diagnosis of suspected parenchymal brain recurrence in aggressive lymphoma. Furthermore, the NGS-MRD assay may enhance clinical risk assessment for CNS recurrence among patients with newly diagnosed lymphomas and help select those who may benefit most from novel approaches to CNS-directed prophylaxis.

The CoVID-TE risk assessment model for venous thromboembolism in hospitalized patients with cancer and COVID-19.

BACKGROUND: Hospitalized patients with COVID-19 have increased risks of venous (VTE) and arterial thromboembolism (ATE). Active cancer diagnosis and treatment are well-known risk factors; however, a risk assessment model (RAM) for VTE in patients with both cancer and COVID-19 is lacking. OBJECTIVES: To assess the incidence of and risk factors for thrombosis in hospitalized patients with cancer and COVID-19. METHODS: Among patients with cancer in the COVID-19 and Cancer Consortium registry (CCC19) cohort study, we assessed the incidence of VTE and ATE within 90 days of COVID-19-associated hospitalization. A multivariable logistic regression model specifically for VTE was built using a priori determined clinical risk factors. A simplified RAM was derived and internally validated using bootstrap. RESULTS: From March 17, 2020 to November 30, 2020, 2804 hospitalized patients were analyzed. The incidence of VTE and ATE was 7.6% and 3.9%, respectively. The incidence of VTE, but not ATE, was higher in patients receiving recent anti-cancer therapy. A simplified RAM for VTE was derived and named CoVID-TE (Cancer subtype high to very-high risk by original Khorana score +1, VTE history +2, ICU admission +2, D-dimer elevation +1, recent systemic anti-cancer Therapy +1, and non-Hispanic Ethnicity +1). The RAM stratified patients into two cohorts (low-risk, 0-2 points, n = 1423 vs. high-risk, 3+ points, n = 1034) where VTE occurred in 4.1% low-risk and 11.3% high-risk patients (c statistic 0.67, 95% confidence interval 0.63-0.71). The RAM performed similarly well in subgroups of patients not on anticoagulant prior to admission and moderately ill patients not requiring direct ICU admission. CONCLUSIONS: Hospitalized patients with cancer and COVID-19 have elevated thrombotic risks. The CoVID-TE RAM for VTE prediction may help real-time data-driven decisions in this vulnerable population.

End-of-life care quality outcomes among Medicare beneficiaries with hematologic malignancies.

Patients with hematologic malignancies are thought to receive more aggressive end-of-life (EOL) care and have suboptimal hospice use compared with patients with solid tumors, but descriptions of EOL outcomes from comprehensive cohorts have been lacking. We used the population-based Surveillance, Epidemiology, and End Results-Medicare dataset to describe hospice use and indicators of aggressive EOL care among Medicare beneficiaries who died of hematologic malignancies in 2008-2015. Overall, 56.5% of decedents used hospice services for median 9 days (interquartile range, 3-27), 33.0% died in an acute hospital setting, 36.8% had an intensive care unit (ICU) admission in the last 30 days of life, and 13.3% received chemotherapy within the last 14 days of life. Hospice use was associated with 96% lower probability of inpatient death (adjusted risk ratio [aRR], 0.038; 95% confidence interval [CI], 0.035-0.042), 44% lower probability of an ICU stay in the last 30 days of life (aRR, 0.56; 95% CI, 0.54-0.57), and 62% decrease in chemotherapy use in the last 14 days of life (aRR, 0.38; 95% CI, 0.35-0.41). Hospice enrollees spent on average 41% fewer days as inpatient during the last month of life (adjusted means ratio, 0.59; 95% CI, 0.57-0.60) and had 38% lower mean Medicare spending in the last month of life (adjusted means ratio, 0.62; 95% CI, 0.61-0.64). These associations were consistent across histologic subgroups. In conclusion, EOL care quality outcomes and hospice enrollment were suboptimal among older decedents with hematologic cancers, but hospice use was associated with a consistent decrease in aggressive care at EOL.

Utilization of COVID-19 Treatments and Clinical Outcomes among Patients with Cancer: A COVID-19 and Cancer Consortium (CCC19) Cohort Study.

Among 2,186 U.S. adults with invasive cancer and laboratory-confirmed SARS-CoV-2 infection, we examined the association of COVID-19 treatments with 30-day all-cause mortality and factors associated with treatment. Logistic regression with multiple adjustments (e.g., comorbidities, cancer status, baseline COVID-19 severity) was performed. Hydroxychloroquine with any other drug was associated with increased mortality versus treatment with any COVID-19 treatment other than hydroxychloroquine or untreated controls; this association was not present with hydroxychloroquine alone. Remdesivir had numerically reduced mortality versus untreated controls that did not reach statistical significance. Baseline COVID-19 severity was strongly associated with receipt of any treatment. Black patients were approximately half as likely to receive remdesivir as white patients. Although observational studies can be limited by potential unmeasured confounding, our findings add to the emerging understanding of patterns of care for patients with cancer and COVID-19 and support evaluation of emerging treatments through inclusive prospective controlled trials. SIGNIFICANCE: Evaluating the potential role of COVID-19 treatments in patients with cancer in a large observational study, there was no statistically significant 30-day all-cause mortality benefit with hydroxychloroquine or high-dose corticosteroids alone or in combination; remdesivir showed potential benefit. Treatment receipt reflects clinical decision-making and suggests disparities in medication access.This article is highlighted in the In This Issue feature, p. 1426.

The return of gemtuzumab ozogamicin: a humanized anti-CD33 monoclonal antibody-drug conjugate for the treatment of newly diagnosed acute myeloid leukemia.

Through the years gemtuzumab ozogamicin (GO) has moved from a panacea in the treatment of acute myeloid leukemia (AML) to a pariah and back again. Early promise of targeted therapy with accelerated approval in the United States in 2000 gave way to fear over increased toxicity in the absence of efficacy, which subsequently resulted in the drug manufacturer voluntarily withdrawing GO from the market in 2010. We outline the history of GO in terms of initial drug development and early clinical trials that ultimately led the way to GO frontline use in AML based on a series of Phase III studies. Among these studies, we discuss the similarities and differences in terms of dosing, frequency, response rates, and toxicities that ultimately led to the re-approval of GO in 2017 based on efficacy, particularly in patients with core-binding factor (CBF) leukemia. Herein, we also review the clinical efficacy of GO in the frontline treatment of acute promyelocytic leukemia, which is based on either initial patient high-risk disease or potential co-morbidities that preclude the use of arsenic trioxide (ATO). Finally, we assess the current evidence for biomarkers aside from initial cytogenetics that may predict a favorable response to GO.

Endothelial to haematopoietic transition contributes to pulmonary arterial hypertension.

AIMS: The pathogenic mechanisms of pulmonary arterial hypertension (PAH) remain unclear, but involve dysfunctional endothelial cells (ECs), dysregulated immunity and inflammation in the lung. We hypothesize that a developmental process called endothelial to haematopoietic transition (EHT) contributes to the pathogenesis of pulmonary hypertension (PH). We sought to determine the role of EHT in mouse models of PH, to characterize specific cell types involved in this process, and to identify potential therapeutic targets to prevent disease progression. METHODS AND RESULTS: When transgenic mice with fluorescence protein ZsGreen-labelled ECs were treated with Sugen/hypoxia (Su/Hx) combination to induce PH, the percentage of ZsGreen+ haematopoietic cells in the peripheral blood, primarily of myeloid lineage, significantly increased. This occurrence coincided with the depletion of bone marrow (BM) ZsGreen+ c-kit+ CD45- endothelial progenitor cells (EPCs), which could be detected accumulating in the lung upon PH-induction. Quantitative RT-PCR based gene array analysis showed that key transcription factors driving haematopoiesis were expressed in these EPCs. When transplanted into lethally irradiated recipient mice, the BM-derived EPCs exhibited long-term engraftment and haematopoietic differentiation capability, indicating these EPCs are haemogenic in nature. Specific inhibition of the critical haematopoietic transcription factor Runx1 blocked the EHT process in vivo, prevented egress of the BM EPCs and ultimately attenuated PH progression in Su/Hx- as well as in monocrotaline-induced PH in mice. Thus, myeloid-skewed EHT promotes the development of PH and inhibition of this process prevents disease progression in mouse models of PH. Furthermore, high levels of Runx1 expression were found in circulating CD34+ CD133+ EPCs isolated from peripheral blood of patients with PH, supporting the clinical relevance of our proposed mechanism of EHT. CONCLUSION: EHT contributes to the pathogenesis of PAH. The transcription factor Runx1 may be a novel therapeutic target for the treatment of PAH.