What is mesothelioma?

Mesothelioma is a tumour of the mesothelium. This is the thin lining (membrane) that covers the outer surface of most of our body's organs. On this page Pleural mesothelioma Peritoneal mesothelioma Rare types of mesothelioma Cell types of mesothelioma More than 2,500 people are diagnosed with mesothelioma in the UK each year. The mesothelium has different names in different parts of the body. For example: • in the chest it’s called the pleura • in the abdomen it’s called the peritoneum. A cancer of the mesothelium is called a malignant mesothelioma. However, it’s usually referred to simply as mesothelioma. There are other tumours of the mesothelium, such as adenomatoid tumours, benign cystic mesotheliomas and solitary fibrous tumours of the pleura. Our cancer information specialists can give you information about these. This section is about malignant mesothelioma. There are two main types of malignant mesothelioma: pleural mesothelioma and peritoneal mesothelioma. Pleural mesothelioma is much more common than peritoneal mesothelioma. Around 9 out of 10 cases (90%) of mesothelioma develop in the pleura, compared with around 1 in 10 (10%) in the peritoneum. Ratio of pleural mesothelioma to peritoneal mesothelioma Ratio of pleural mesothelioma to peritoneal mesothelioma. View a large copy of the infographic showing the ratio of pleural mesothelioma to peritoneal mesothelioma Pleural mesothelioma Back to top The pleura is the smooth outer lining (membrane) that covers each lung. It has two layers: the inner (visceral) layer, which is next to the lung, and the outer (parietal) layer, which lines the chest wall. The two layers of the pleura are usually in contact and slide over each other as we breathe. The layers produce fluid, which allows them to move smoothly over each other. When mesothelioma develops in the pleura (pleural mesothelioma), the delicate layers of the pleura thicken and may press inwards on the lung. Fluid may also collect between the two layers, which is known as a pleural effusion. Pleural mesothelioma can sometimes spread to the lymph nodes in the chest or above the collarbone, or elsewhere in the body. Structure of the lungs and pleura Structure of the lungs and pleura. View a large copy of the infographic showing the structure of the lungs and pleura Peritoneal mesothelioma Back to top The outer lining (membrane) that covers the organs in the abdomen is known as the peritoneum. The peritoneum helps protect the organs of the abdomen and keep them in place. It also has two layers: the inner (visceral) layer, which is next to the abdominal organs, and the outer (parietal) layer, which lines the abdominal wall. Side view of the abdomen Side view of the abdomen. The peritoneum is shown as the thick line surrounding the abdominal organs. View a large version of the image showing the side view of the abdomen Mesothelioma in the peritoneum is called peritoneal mesothelioma. It causes thickening of the peritoneum and a collection of fluid in the abdomen. The collection of fluid is called ascites and causes swelling of the tummy (abdomen). Rare types of mesothelioma Back to top Very rarely, a mesothelioma may develop in the outer lining of the heart (pericardial mesothelioma) or in the outer lining of the testes (testicular mesothelioma). These are not discussed in this booklet. If you’d like information about them, contact our cancer information specialists on 0808 808 00 00. Cell types of mesothelioma Back to top Pleural and peritoneal mesothelioma can also be grouped according to how the cells look under a microscope. There are three main types: • epithelial – this is the most common • sarcomatoid (fibrous) • mixed (biphasic) – this has both epithelial and sarcomatoid cells. Knowing the type of cell involved may give your doctors an idea of how well the disease will respond to treatment.