Tobacco smoking is associated with many forms of cancer,[19] and causes 80% of lung cancer.[20] Decades of research has demonstrated the link between tobacco use and cancer in the lung, larynx, head, neck, stomach, bladder, kidney, esophagus and pancreas.[21] There is some evidence suggesting a small increased risk of developing myeloid leukemia, squamous cell sinonasal cancer, liver cancer, colorectal cancer, cancers of the gallbladder, the adrenal gland, the small intestine, and various childhood cancers.[21] Tobacco smoke contains over fifty known carcinogens, including nitrosamines and polycyclic aromatic hydrocarbons.[22] Tobacco is responsible for about one in three of all cancer deaths in the developed world,[19] and about one in five worldwide.[22] Lung cancer death rates in the United States have mirrored smoking patterns, with increases in smoking followed by dramatic increases in lung cancer death rates and, more recently, decreases in smoking rates since the 1950s followed by decreases in lung cancer death rates in men since 1990.[23][24] However, the numbers of smokers worldwide is still rising, leading to what some organizations have described as the tobacco epidemic.[25]