Review
Pulmonary tumor embolism: a review of the literature

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Abstract

Dyspnea in a patient with cancer may have several causes, including infection, thromboembolism, metastases, and therapeutically induced cardiopulmonary disease. Pulmonary tumor embolism is an uncommon cause. Occlusion of the pulmonary microvasculature by tumor cells and associated thrombi can produce a subacute and progressive clinical picture that resembles thromboembolic disease. Unfortunately, microscopic tumor embolism is recognized rarely before death because of difficulty in establishing the diagnosis. We provide a review of the literature about the evaluation and diagnosis of this rare clinical entity.

Section snippets

Clinical presentation

The clinical presentation of nonmassive pulmonary tumor embolism reflects its pathophysiology, specifically progressive cor pulmonale over weeks to months. The most common presenting complaint is dyspnea, in 57% to 100% of cases 3, 4, 5. Cough, chest, and abdominal pain (due to liver metastases or hepatic venous congestion) have also been reported. Signs of elevated pulmonary pressures include ascites, an augmented second heart sound, and peripheral edema. However, the symptoms are usually more

Prevalence

Autopsy series estimate that the incidence of pulmonary tumor embolism is between 3% and 26% among patients with solid tumors 3, 6, 7. Retrospective chart reviews demonstrate that only 8% of patients with pathological evidence for tumor emboli have documented morbidity or mortality attributable to the tumor emboli 3, 7. The majority of reported cases occur in association with breast, lung, or gastric carcinoma, an observation that may simply reflect the relative prevalence of those tumors (Table

Pathology

In a series of 19 cases, Soares et al found tumor emboli involving multiple levels of the microscopic pulmonary vasculature, from the elastic arteries down to the alveolar septal capillaries (4). Kane et al's retrospective review of 16 patients with solid tumors revealed that anywhere from 7% to 81% of the pulmonary arteries in these patients contained emboli (3). Although 8 of these patients had unexplained dyspnea consistent with pulmonary hypertension, the presence of symptoms did not

Pathophysiology

How tumor emboli cause pulmonary hypertension and subacute cor pulmonale is unclear. Dissemination of cancer occurs primarily via a hematogenous route, and the most common site for metastatic disease is the lung. The eventual outcome of malignant cells in the lung—metastasis, invasion of lymphatics, development of pulmonary hypertension, or clearance of the cells—is the result of interactions between signaling pathways that affect angiogenesis, apoptosis, and inflammation (6). Many

Diagnosis

Establishing the diagnosis of pulmonary tumor embolism can be difficult. Clinicians must entertain common diagnoses such as infection, thromboembolism, side effects of toxic chemotherapeutic regimens, and other pulmonary manifestations of the primary neoplasm. Hypoxemia with a normal chest radiograph are the typical findings in a patient with tumor emboli, whereas in cases of infection, interstitial fibrosis, or lymphatic spread, the plain films may be diagnostic. In the first published autopsy

Conclusion

Microscopic pulmonary tumor embolism should be considered in the differential diagnosis of a patient with cancer who presents with subacute dyspnea. This rare and poorly understood entity is underrecognized before death. Even in the symptomatic patient, identifying pulmonary tumor emboli can be challenging due to nonspecific results from radiographic and nuclear medicine studies. The judicious use of multiple diagnostic tests, including ventilation-perfusion scanning and pulmonary arterial

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