For patients with cancer complaining of acute shortness of breath, venous thromboembolism (VTE) is often at the top of the differential diagnosis.

The hypercoaguable state that cancer causes, along with the potential for extended time periods of immobility secondary to pain or chemotherapy, places these patients at higher risk for developing clots and associated pulmonary embolism (PE). 

Although ruling out VTE is an important part of the acute shortness of breath work-up for a patient with cancer, the possibility of a tumor embolus exists and should also be considered as a differential diagnosis.

Tumor cells can gain access to the primary circulation of the body through direct invasion of the vasculature.  If these cells are 10 microns or greater in size, they can become trapped within the pulmonary blood vessels, which can lead to compromised circulation and oxygenation. Although tumor emboli can be an unfortunate result of cancer and typically carry a poor prognosis, they are not considered metastases. 

Up to one quarter of all patients who die from cancer are found to have tumor emboli.1 Patients with kidney, liver, lung, and ovarian cancer, as well as adenocarcinomas (eg, breast, stomach, and colon), have been reported to be more likely to have tumor emboli compared with other types of cancer.2

Patients with cancer who have with tumor emboli present with similar symptoms as patients with VTE.  These patients can present with shortness of breath, dyspnea on exertion, pleuritic chest pain, cough, general malaise, and palpitations.  Therefore, it can often be very difficult to discern the two diagnoses.  Ventilation/perfusion scans in patients with tumor emboli usually show multiple perfusion defects in the periphery, which is a finding similar to patients with fat emboli.

Tumor emboli typically evolve over time, so echocardiography can show elevated mean pulmonary artery pressures greater than 50 mmHg.  In comparison, VTE are usually more acute, so mean pulmonary artery pressures tend to be lower than 40 mmHg. 

Positron emission tomography (PET) scans can also be used to differentiate tumor emboli from VTE since tumor emboli will “light up” more on PET scans.  Lung biopsy is the definitive way to diagnose tumor emboli; however, this is not performed as frequently as other diagnostic tests since it is more invasive.

Treatment for tumor emboli is relatively conservative with supportive care and targeted chemotherapy for the main tumor causing the emboli.  Inferior vena cava filters and embolectomies are rarely used and only performed in clinical scenarios in which there are large tumor emboli identified below the diaphragm.

Since VTE and tumor emboli that occur in patients with cancer can present very similarly, both diagnoses should be considered when the patient is complaining of shortness of breath or dyspnea on exertion.  The most commonly implicated cancers with tumor emboli should be kept in mind along with the subtle ways to distinguish the two diagnoses based on imaging.


References

1. Goldhaber SZ, Dricker E, Buring JE, et al. Clinical suspicion of autopsy-proven thrombotic and tumor pulmonary embolism in cancer patients. Am Heart J. 1987 Dec;114(6):1432-5.

2. Sakuma M, Fukui S, Nakamura M, et al. Cancer and pulmonary embolism: thrombotic embolism, tumor embolism, and tumor invasion into a large vein. Circ J. 2006 Jun;70(6):744-9.