This is a randomized control trial of patients with suspected malignant pleural effusions to compare whether patients who have a thoracentesis or pleuroscopy (pleural biopsy) obtain an adequate biopsy, achieve a diagnosis, and begin cancer-directed therapy faster.

This is a randomized control trial of patients with suspected malignant pleural effusions comparing patients who undergo either pleuroscopy or thoracentesis as the first diagnostic test. Both procedures are considered standard of care for this diagnosis but it is unknown which one provides more adequate biopsy samples and achieves faster diagnosis and shorter time to oncologic treatment. Currently, most patients undergo thoracentesis first and, if this is inadequate for diagnosis, they then undergo pleuroscopy for further biopsy samples. This study seeks to assess whether patients who undergo pleuroscopy as the first test obtain adequate biopsy samples and a faster path to further oncologic care compared to patients who undergo thoracentesis first. Patients will be recruited and randomized in a 1:1 manner.

Ultrasound is routinely used prior to the procedure and a chest x-ray is done after the procedure. Any other imaging will be determined by clinic need only. No imaging will be done for research purposes. No additional samples will be collected other than what is necessary for diagnostic purposes. In patients who have a non-diagnostic thoracentesis, the participants will be referred for pleuroscopy as the next diagnostic step. In the rare case that pleuroscopy does not achieve adequate diagnosis, the next step would be a liquid biopsy (non-invasive serologic testing for oncologic markers.) The need for liquid biopsy in participants in this study will be determined on a case-by-case basis depending on the clinical concern for malignancy.

Inclusion Criteria:

• Referral for diagnostic pleural procedure.
• Age ≥ 18 years.
• Suspected malignant pleural effusion (Suggestive radiologic appearance (based on computed tomography or positron emission tomography) OR suspected cancer with associated effusion.)

Exclusion Criteria:

• Inability to provide informed consent.
• Needs emergent drainage.
• Pleural effusion is known to be malignant.
• Suspected transudative, infectious or inflammatory effusion etiology.
• Having prior inconclusive/non-diagnostic thoracentesis or pleuroscopy.
• Patient is deemed by the clinical team to be more appropriate for VATS biopsy.
• Terminally ill patients in whom a diagnosis will not change management, or who is unlikely to be a candidate for oncological treatment due to significant comorbidities.
• Pregnancy

All of the individual participant data collected during the trial, after deidentification.

Immediately following publication. No end date.

Investigators whose proposed use of the data has been approved by an independent review committee ('learned intermediary') identified for this purpose.

Any purpose. Proposals should be directed to udit.chaddha@mssm.edu. To gain access, data requestors will need to sign a data access agreement. Data are available for 5 years at a third party website (Link tbd).