1.6What mesothelioma is, and where it grows

Most organs in your body sit inside a thin, slippery sheet of tissue called the mesothelium. It’s what lets your lungs slide inside your chest, your bowel move inside your abdomen, your heartbeat inside its sac. Mesothelioma is a cancer of that sheet.

It comes in four locations, named after where it starts:

Pleural mesothelioma— in the lining around the lungs. This is the most common form, around 9 in 10 UK cases. Early symptoms include breathlessness, chest pain, a persistent cough, weight loss, and sometimes a build-up of fluid in the chest called a pleural effusion.

Peritoneal mesothelioma— in the lining of the abdomen. Around 1 in 10 UK cases. Symptoms are abdominal swelling, pain, a change in bowel habit and weight loss. Peritoneal cases are usually discussed at a national multidisciplinary team (MDT) based at Basingstoke and Alton Hospitals, which is the UK’s specialist peritoneal centre.

Pericardial mesothelioma— in the sac around the heart. Rare, fewer than 1% of cases.

Testicular mesothelioma— in the lining around the testicle. Rarer still.

Three other words you’ll meet in the histology report:

• Epithelioid— the most common cell type and usually the most treatable.
• Sarcomatoid— the least common and generally the hardest to treat.
• Biphasic— a mix of the two.

We’ve put this list early because the histology subtype matters for treatment choices, for prognosis and for clinical trial eligibility. We’ve kept it brief because none of these labels are a verdict on what’s going to happen next for you. Your team will explain how your particular tumour behaves.