Mesothelioma is a cancer of the thin membrane that lines the chest and abdomen. Around 2500 people in the UK are diagnosed with mesothelioma each year and the median survival is approximately 8.5 months. Exposure to asbestos is the most common cause although the cancer does not usually become apparent until 40-60 years after exposure. Anti-cancer drugs (chemotherapy) are usually given to help treat mesothelioma and sometimes lung-sparing surgery (pleurectomy decortication) is undertaken. However, it is not known if this surgery, in addition to chemotherapy, can increase survival and improve the quality of life for patients. The aim of the MARS2 study is to compare surgery - (extended) pleurectomy decortication - with no surgery with respect to overall survival, cost-effectiveness and quality of life. Patients will be followed up by phone at regular intervals for 2 years. Patients will be asked to complete and return a Quality of Life Questionnaire at these time points.

MARS 2 also includes an optional 'Information study', where consenting patients may be interviewed or have their consultations audio-recorded. The aim of the Information study is to explore how a patient makes a decision to take part in research or not, with the overall aim of improving recruitment to clinical trials.

Inclusion criteria:

1. 16 years of age or over
2. Tissue (cytology or histology) confirmed epithelioid, sarcomatoid or biphasic mesothelioma
3. Disease confined to one hemi-thorax based on CT assessment
4. Disease deemed surgically resectable
5. Fit for surgery
6. Capacity to provide written informed consent to participate in the trial

Exclusion criteria:

1. Severe shortness of breath (this is defined as an Eastern Cooperative Oncology Group (ECOG) status ≥ 2, or if lung function tests are performed: pre-operative forced expiratory volume after one second (FEV1) or transfer factor of the lung for carbon monoxide (TLco) less than 20%)
2. Serious concomitant disorder that would compromise participant safety during surgery (e.g. evidence of end organ failure)
3. Severe heart failure (this is defined as NYHA III or IV or if an echocardiogram is performed an ejection fraction less than 30%)
4. End stage kidney failure requiring dialysis
5. Liver failure (e.g. encephalopathy and/or coagulation abnormalities)
6. Prisoner
7. Patient lacks capacity to consent
8. Existing co-enrolment in another interventional clinical trial that aims to improve survival