According to the American Cancer Society, smoking accounts for a number of cancers and for at least 30 percent of all cancer-related deaths. Many known carcinogens, substances known to directly cause cancer, are present in cigarettes. The risk of developing any of the smoking-related cancers increases with exposure. In other words, both the number of cigarettes one smokes a day as well as the number of years one smokes increase the risk of developing cancer.
Lung Cancer
Lung cancer ranks as the second most common cancer diagnosed for men and women in the U.S. and leads in cancer-related deaths. Duration of smoking and amount smoked affects the level of lung cancer risk. The National Cancer Institute notes that 90 percent of all lung cancer deaths among men and 80 percent among women relate directly to smoking.
Oral and Digestive Cancers
Oral cancers include cancers of the lips and inside the mouth or oral cavity. The latter includes the tongue and under the tongue, the inside lining of the cheeks and lips, the bony part of the top of the mouth known as the hard palate, the gums and the small area behind the wisdom teeth. The American Cancer Society points out that at least 90 percent of oral cancers relate to smoking and tobacco use.
There also seems to be some evidence that smoking increases the risk of developing colorectal cancer. Colorectal means the entire colon, or large intestine, including the lower portion called the rectum. Not only does smoking appear to cause colorectal cancer, but additionally seems to increase the risk for precancerous colon lesions to recur, according to the National Cancer Institute. Other digestive cancers associated with smoking include cancers of the pharynx, the esophagus, the stomach, the liver and the pancreas.
Cervical Cancer
While most cervical cancer results from an infection with the Human Papilloma Virus, or HPV, long-standing evidence shows smoking can also cause cervical cancer, states the National Cancer Institute. Smoking may double or even triple cervical cancer risk, particularly among women exposed to HPV. Even exposure to secondhand smoke can cause cervical cancer.
Breast and Prostate Cancers
Although most studies have found little connection between breast cancer and smoking, in the report "Canadian Expert Panel on Tobacco Smoke and Breast Cancer Risk," an expert panel presented their belief that smoking does cause breast cancer, most notably among long-term smokers who had a particular gene that leads to more susceptibility to carcinogens. About half of North American women have this type of gene; and in the presence of smoking, this could significantly increase their risk for breast cancer.
While there is little evidence that smoking causes prostate cancer, a study published in "The Journal of Urology" concluded that smoking does seem to increase the growth and spread of prostate cancer.
Other Cancers
Smoking causes or contributes to a number of other cancers as well, notes the American Cancer Society. These include cancers of the larynx, kidney, bladder and some types of leukemia.
