Such tumors are called malignant tumors, or cancer. Because of the different manner in which tissue cells in the same organ system may respond to varying types of exposure to cancer producing agents, several different types of cancer may be found in any organ. This is well illustrated by the primary cancers affecting the lung, which are described below. Because it spreads rapidly from its characteristically central location, surgery is rarely the best treatment. As cigarette smoking is the major cause of lung cancer today, it is important to understand how it affects the lungs.
Smoking causes lung cancer in two ways.
First of all smoke inhalation damages the normal cleansing processes by which the lung protects itself from injury. Hair like cilia on these cells beat in rhythmic fashion to move the mucus continually upwards from the lungs, removing any inhaled particles, which have been trapped in the sticky mucus. When these changes have occurred, the lung can no longer keep itself clean. Consequently, cancer n producing agents in the cigarette smoke remain trapped in the mucus on the surface lining on the airway long enough to pass into the cells before these substances can be removed by coughing, the only cleansing mechanism which remains. Cigarette smoking is therefore a cancer n producing form of pollution in the inhaled air, which possesses not only the ability to destroy the cleansing mechanism, but also dangerous, cancer n producing chemicals.