Patient inclusion cannot be completed within time limits

Recurrent unilateral, non-infectious pleural exudate is suspicious for primary or secondary pleural malignancy. Both conditions are associated with 5-year survival of 10%. Work-up is difficult, as the pleural surface is large and <33% of pleural malignancies shed malignant cells to the pleural fluid. Even so, additional tissue biopsies are needed for establishing mutation status for targeted therapies.

Optimal imaging to guide tissue sampling is pivotal. PET-CT has higher sensitivity than conventional CT for detecting malignant lesions >10mm. However, no randomised trial has investigated differences in diagnostic accuracy, time-to-diagnosis, or economics. Falsely PET-positive lesions in e.g. colon, however, lead to more derived tests than do CT alone.

Gold standard for pleural tissue sampling is the surgical (VATS) thoracoscopy, allowing direct visual guiding of tissue sampling from all pleural surfaces. Yet, globally the medical (pleuroscopy) thoracoscopy is more widely used: cheaper, outpatient procedure, but allows only sampling from the parietal pleura. To date, no randomised studies have compared medical and surgical thoracoscopy concerning diagnostic hit rates, adverse events, or economics.

Investigators will perform two randomized studies to investigate whether

1. PET/CT is comparable to CT alone
2. VATS is comparable to pleuroscopy concerning hit rate, total investigations performed, time-to-diagnosis.

Inclusion Criteria:

1. Patients with recurrent pleural effusion of unknown origin after a first pleural tap according to BTS guidelines.
2. Indication for thoracoscopy according to BTS guidelines.
3. Patients accept further investigation according to Danish and BTS guidelines.
4. Have received oral and written consent and agreed.
5. At the time of inclusion, above 18 years of age.

Exclusion Criteria:

1. Female patients: pregnancy or breastfeeding.
2. Lack of language comprehension.
3. Legally incompetent patients.
4. Life expectancy less than 3 month.
5. Contraindications to pleural tissue sampling.