Cigarette smoke has been associated with 17 different types of cancer that claim the lives of over 6 million people each year. The cancer most commonly associated with cigarettes is lung cancer but it is known that incidences of oral, bladder, liver, and stomach cancer are associated with smoking. Cigarettes contain a mixture of harmful chemicals, many of which are known to be carcinogenic. These compounds cause cancer by damaging the DNA within a cell and causing mutations that alter the abundance or function of certain proteins (refresher on DNA, RNA and proteins here). Cancer can develop when these mutations are in pieces of DNA that code for proteins controlling cell growth and movement. Scientists analyzed the cancer DNA of 5243 tumors known to be associated with smoking in an effort to understand what sorts of tobacco specific mutations are present in the cells of these cancers.
The scientists, working out of the United States, identified 150 DNA mutations in the lung caused by smoking one pack of cigarettes a day for a year. These mutations contributed to the development of small cell lung cancer, lung adenocarcinomas, and squamous lung cancer. In addition, smoking a pack a day for a year resulted in 97 mutations in the DNA from the larynx, 39 from the pharynx, 23 in the mouth, 18 in the bladder, and 6 in the liver. The researchers also identified different mechanisms of DNA mutations depending on if the organ came into direct contact with the cigarette smoke or not. In the lung, carcinogens in cigarette smoke are likely to directly mutate the DNA in the cells. In sites not directly exposed to cigarette smoke, the mutations seemed to be caused by a speeding up of the cellular clock that results in age related mutations.
This result gives strong evidence that DNA mutations caused by cigarettes are the reason for the increase in cancer risk in smokers. While this may not be surprising, the results are important for understanding the mutational steps necessary for cancer to form in response to cigarette smoke so that we can understand proper treatment options and prevention steps. Of course, the most surefire way to prevent lung cancer and other forms of cancer is to stop smoking and live a healthy life style.