1 Smokeless tobacco products are a major source of cancer-causing nitrosamines and a known cause of human cancer. 2  They increase the risk of developing cancer of the mouth and throat, esophagus (swallowing tube), and pancreas. Tobacco use accounts for at least 30% of all cancer deaths, causing 87% of lung cancer deaths in men, and 70% of lung cancer deaths in women. ( 2 Source: Cancer Facts & Figures 2014).