mesothelioma A benign (noncancerous) or malignant (cancerous) tumor affecting the lining of the chest or abdomen. Exposure to asbestos particles in the air increases the risk of developing malignant mesothelioma.

asbestos (as-BES-tus) A natural material that is made of tiny fibers. Asbestos can cause several serious diseases, including cancer.

malignant mesothelioma A rare type of cancer in which malignant cells are found in the sac lining the chest or abdomen. Exposure to airborne asbestos particles increases one’s risk of developing malignant mesothelioma.

stage I malignant mesothelioma Cancer is found in the lining of the chest wall and may also be found in the lining of the lung, the lining of the diaphragm (the thin muscle below the lungs and heart that separates the chest from the abdomen), or the lining of the sac that covers the heart on the same side of the chest. Also called localized malignant mesothelioma.

stage II malignant mesothelioma Cancer is found in the lining of the chest wall and the lymph nodes on the same side of the chest. Cancer may also be found in the lining of the lung, the lining of the diaphragm (the thin muscle below the lungs and heart that separates the chest from the abdomen), or the lining of the sac that covers the heart on the same side of the chest. Stages II, III, and IV malignant mesothelioma are also called advanced malignant mesothelioma.

stage III malignant mesothelioma Cancer has spread to the chest wall, mediastinum, heart, lining of the peritoneum, and/or beyond the diaphragm. Cancer may also have spread to lymph nodes on the other side of the chest or outside the chest. Stages II, III, and IV malignant mesothelioma are also called advanced malignant mesothelioma.

stage IV malignant mesothelioma Cancer has spread to distant organs or tissues. Stages II, III, and IV malignant mesothelioma are also called advanced malignant mesothelioma.