Mesothelioma

Malignant mesothelioma is a rare, aggressive cancer. It starts in mesothelial cells, the cells that make up the thin lining covering the outside of organs such as the lungs, and most of the time it shows up in the pleura, the lining that surrounds each lung. One part of the pleura, the parietal pleura, lines the inside of the chest wall, and another, the visceral pleura, wraps around the lung itself. Picture the wallpaper on the walls of a room and the cover on a cushion sitting in that same room.

This cancer is strongly tied to asbestos, a material whose fibers can be breathed in. Breathing in those fibers can inflame the pleura over and over. It can also throw off mitosis, the process a cell uses to divide; switch on proto-oncogenes, genes that control cell growth and that, when they're too active, push the cell to multiply out of control; and generate free radicals, unstable molecules that damage whatever they touch. Together, all of that damage contributes to the disease.

The tumor usually starts as nodules, small lumps of tissue, on the parietal pleura (the wallpaper on the wall) and often reaches the visceral pleura (the cover on the lung). The most common first finding is a pleural effusion, meaning fluid that collects between the layers of the pleura. And often, the clue that gives it away is shortness of breath.