Harvard report on cancer prevention. Causes of human cancer. Smoking.

Cigarette smoking increases risk of a wide range of cancers, and early onset of smoking is related particularly to risk of lung cancer and colon cancer. The adverse effects of smoking may occur at different points in the pathway to cancer. Smoking may act early, as seen with colon cancer; it may act early and late, as with lung cancer; or it may act only late in the pathway to cancer, as seen with cancer of the pancreas. The benefits of quitting are substantial and quite rapid for cancer, particularly for cancers of the lung and pancreas.