The investigators want to determine the incidence of malignant disease, type of malignant disease and overall survival in patients diagnosed with NSP after VATS.

Using Landspatientregisteret (LPR) (the National Patient register) the investigators will identify patients who have received a thoracoscopic pleural-biopsy using the SKS-codes KGAC01 and/or KGAA31 and/or KGAC00. From LPR and Cancerregisteret (the National Cancer-register) the investigators will receive diagnosis and additional descriptive data. From dødsårsagsregisteret (the National cause-of-death-register) death date and further descriptive data will be acquired.

Patients with NSP will be identified as patients with no diagnosis six months after pleural-biopsy, despite a thorough investigation.

Patients with a malignant effusion and non-malignant effusion (with known cause) will be used for survival analysis and comparison.

Data Data will be registered in the individual patients CRF (Case Report File) (digital) and will be transferred to a database-program for further processing. Background-variables will be used to describe the study population. Only study-coordinators will have access to data. All data including back-up will be stored and kept in a locked cupboard in a locked room. Only study coordinators possess relevant keys.

Statistics The investigators define significance level (α) as 0.05, and power (β) as 0.80. Descriptive data will be analysed using nonparametric statistics: Chi2-test for categorical data and Mann-Whitney for discrete data. Statistical significance is defined as: p-value < 0.05.

The overall survival of patients with NSP will be analysed using a Caplan-Meier plot and comparison of NSP patients to patients with malignant pleural-effusion the investigators use the Logrank test.

All statistical tests is conducted using STATA14 (4905 Lakeway Dr., College Station, TX 77845).

Ethics This study will not require the approval from Videnskabsetisk komité (the Health Research Ethics Committee), but approval will be sought from Datatilsynet (the Danish Data Protection Agency).

All results will be stored and analysed by computer, and the patients' anonymity will be secured according to the national laws. The data will be stored (anonymised), after completion of the study: data containing cpr.-numbers will be stored behind double-lock at the department.

No patients or investigators have economic incentives for completing the project.

Economy

Expenses related to gathering of data including contact with LPR, Dødsårsagsregisteret and the Danish Cancer Register are already financed through primary investigators PhD-project.

Publication The results from the study will be presented at international scientific congresses and published in international journals. Positive as well as negative results will be published. The scientists right to freely publish the results cannot be limited. All information will be passed anonymously.

The order of authors will follow the Vancouver Declaration, and will thus reflect the amount and significance of work relevant to the specific manuscript.

Inclusion Criteria:

• All patients with a VATS thoracoscopy

Exclusion Criteria:

• None

All patients with a VATS thoracoscopy