Most people accept that smoking causes cancer, but the detailed mechanisms behind that are not completely understood. In a new study, researchers solved part of the puzzle when they discovered that smoking causes extensive damage to DNA in the genome of the tissues directly exposed to smoke and also in organs all over the body.
Smoking is associated with at least 17 types of cancer, and it contributes to the deaths of six million people every year. The World Health Organization estimates there will be at least one billion tobacco-related deaths in this century. Smoking is usually associated with lung cancer, but it also causes cancers of the mouth, throat, bladder, liver, stomach, ovaries, cervix, kidney, pancreas, colon and even leukemia.
Tobacco smoke is a complex mixture of chemicals including at least 60 known carcinogens, which cause damage to DNA. If the damage is not corrected, the mutation is passed on when cells divide. Scientists have long known that certain genes lead to cancer when they are mutated. The process of a gene causing cancer can be random and complex, and it can take a long time. As DNA damage and mutations accumulate, the likelihood of a cell turning cancerous increases. The total number of mutations varies among individuals, but increases in the mutational rate accelerate the pathway to cancer.
Any process that leads to mutations in cells leaves a characteristic signature of such changes. Researchers got samples of over 5,000 cancers from both smokers and non-smokers and compared the DNA of similar cancers between the two groups in hopes of finding the signatures.
The study identified several mutation signatures linked to smoking that were significantly different from other regions of the DNA. One such signature, present in all the samples from smokers, appears to increase the rate at which mutations occur. These mutations do not appear to be caused by the smoke directly, but by the changes in cellular mechanisms that mutate the DNA. Another signature was found in all tissues that were directly exposed to smoke, indicating that it was caused by the carcinogens in smoke.
It is not clear what mechanisms cause mutations in the tissues throughout the body that are not exposed to smoke. Behaviors such as drinking alcohol, natural radiation sources and environmental pollutants could also contribute to the accumulation of cancer-causing mutations. Regardless of how these mutations in DNA happen, they represent permanent changes to genetic information. If cells are also exposed to cigarette smoke, they will accumulate additional mutations, and it is only a matter of time before the combination of mutations in cancer-causing genes leads to the development of a tumor.
If you don’t quit smoking for yourself, do it for your spouse, kids, friends and co-workers. Secondhand smoke inhaled by people around you and third-hand smoke accumulated on surfaces in homes and cars puts non-smokers at higher risk of cancer. This new study shows just how dangerous smoking is for your body, and highlights the importance of quitting the habit as soon as possible. Or better yet― don’t start.
For help quitting, call 1-800-QUIT-NOW.
Medical Discovery News is hosted by professors Norbert Herzog at Quinnipiac University, and David Niesel of the University of Texas Medical Branch. Learn more at www.medicaldiscoverynews.com.