Unsuspected Pulmonary Embolism in Cancer Patients: A Multicenter, International, Prospective, Observational Study
Authors: Bleker Suzanne , van Es Nick , Kleinjan Ankie , Büller Harry R. , Middeldorp Saskia , Dinisio Marcello 
Published: October 2019

Abstract
INTRODUCTION
Clinically unsuspected pulmonary embolism (UPE) is frequently diagnosed in cancer patients undergoing routine computed tomography scans for staging purposes or treatment response evaluation. The reported incidence of UPE ranges from 1% to 5%, and is likely to increase further with the improvements of imaging techniques.
Current guidelines suggest that UPE should receive similar initial and long-term anticoagulant treatment as for symptomatic PE. However, direct evidence is scarce. Selected subgroups of cancer patients with UPE such as those with subsegmental UPE may be treated conservatively by withholding anticoagulation as subsegmental PE seems to have a more benign course than more proximal PE.
AIM
The aim of this study is to evaluate the current treatment approaches for UPE and to assess their efficacy and safety in a large prospective cohort of cancer patients.
MATERIAL AND METHODS
This is a prospective, observational, multicenter, international study in cancer patients with UPE. Adult patients with UPE are consecutively included in the study. Patients already treated with anticoagulant therapy and patients with a life expectancy of less than 3 months are not eligible for participation. All patients will be followed for 12 months after diagnosis. The outcome variables (recurrent VTE, bleeding and mortality) will be recorded at 3, 6 and 12 months of follow-up. All outcomes will be adjudicated by a central independent adjudication committee. To enable sufficient power for a comparison of VTE recurrence rate between patients with (sub)segmental PE and those with central and/or lobar PE, a sample size of 610 patients was calculated based on an assumed overall recurrent VTE rate of 13% and an odds of 3:1 of (sub)segmental PE versus central PE.
RESULTS
From April 2012 to June 2014 a total of 123 cancer patients with UPE were enrolled, of whom 71 (57.8%) had lobar or central PE. 116 patients (94.3%) were treated and 83.6% of them received low molecular weight heparin (LMWH) as the initial and long-term treatment. The baseline characteristics are depicted in Table 1.
The incidence of VTE recurrence, bleeding and mortality at 3 months of follow-up are 4.9%, 8.5% and 11%, respectively. At 6 months these rates are 4.9%, 18%, and 18.1% and at 12 months of follow-up 4.9%, 18% and 43.1%, respectively. Follow-up and central adjudication are being completed and an update of this ongoing project will be presented.
CONCLUSIONS
The results from this study will give insight in the current treatment strategies in cancer patients with UPE. Important prospective data on the outcome of UPE in terms of recurrent VTE, bleeding and mortality in cancer patients will be generated, especially regarding the outcome of (sub)segmental UPE. These distally located PE may have a more benign course compared with lobar and/or central PE thus requiring no or short anticoagulant treatment. This will be tested in subsequent randomized trials.
Baseline characteristics of cancer patients with UPE.
Table 1 Table 1.
SD = standard deviation; LMWH = low-molecular weight heparin; UFH = unfractionated heparin

Disclosures
No relevant conflicts of interest to declare.