The malignant pleural effusion (MPE) incidence in the United States is estimated to be more than 150,000 cases annually (1). Most of the MPEs are symptomatic and commonly present with dyspnea, dry cough, dull chest pain and constitutional symptoms (2). While there is a fair amount of data about symptomatic MPEs, including epidemiology, clinical presentation and treatment options, the management of asymptomatic MPEs is mostly through observation (3,4).
Small studies showed that the prevalence of asymptomatic MPEs varies from 14% to 41% (5,6). Data regarding the size of asymptomatic MPE is not clear in the literature. After diagnostic thoracentesis, asymptomatic MPEs are managed mainly by observation, and other interventions are only performed if symptoms develop.
The life expectancy of patients with MPE is limited to an average of 3 to 12 months (7). The goal of managing MPE is to palliate symptoms using one of the available approaches such as repeated thoracentesis, chest tube thoracostomy with pleurodesis, indwelling pleural catheter placement with or without concomitant pleurodesis and in some cases surgical pleurodesis (3).
In the era of new cancer agents using mutations-targeted drugs and immunotherapy, many patients with metastatic disease are expected to have longer survival (8,9). Moreover, patients with non-lung cancer MPEs such as breast, colon, and lymphoma have a better outcome compared to those with MPEs of lung cancer etiology (3,10).
Long standing MPE’s have been associated with trapped lung and loculation (11). MPE’s affect lung volumes, decrease total lung capacity, and may cause restrictive lung physiology (12). The larger the MPE, the more the impact is on lung function. Typically, asymptomatic MPE’s are managed with observation whether they are mild, moderate, or large.
It is not clearly known how many asymptomatic MPE’s become symptomatic, and it’s hard to predict which asymptomatic MPE will eventually become symptomatic. This probably depends on the size of the effusion, type of primary malignancy and the general medical condition of the patient. In one small group of patients with MPE investigated by Tremblay et al., only one patient out of fourteen (7.1%) developed symptoms over time (6). Others stated that all MPE’s eventually become symptomatic at one point of their disease (13).
In patients with symptomatic MPE’s caused by rapidly-responsive malignant disease, it is reasonable to observe these patients after starting systemic therapy. Many of these effusions will decrease or resolve with cancer therapy, and therapeutic thoracentesis can be performed as needed (3,14). Other clinical situations may justify treating asymptomatic MPE with drainage.
Herrtedt et al. compared 30 patients with small cell lung cancer (SCLC) with MPE with 30 patients with SCLC without MPE. They showed that in patients with MPE, initial chemotherapy led to a significant drop in blood cell and thrombocyte counts compared to patients without MPE, which necessitated a reduction in the chemotherapy dose. This finding suggests that some chemotherapeutic agents may accumulate in the pleural fluid and cause toxicity (15).
Whether asymptomatic MPEs should all be observed without any intervention warrants more investigation. Small MPEs will probably not benefit from intervention, but in patients with moderate and large MPEs, the management should probably be personalized, and more studies are needed to investigate this hypothesis. Patients with asymptomatic moderate to large MPEs, which negatively impact lung function, may be more vulnerable to hypoxia or other respiratory symptoms if they subsequently develop new lung diseases such as pneumonia or contralateral pleural effusions. Therefore, patients with malignancies who are likely to have long-term survival should be considered for intervention to manage their asymptomatic moderate to large MPEs. Nevertheless, more investigational trials are warranted before making such recommendations.
Conflicts of Interest: The authors have no conflicts of interest to declare.
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