Fifty years ago, a landmark study by the U.S. Surgeon General identified the links between tobacco use, cancer and death. In the half century since, smoking rates in the U.S. have been cut by nearly 50 percent and an estimated 8 million American lives have been saved from premature smoking-related deaths.

The number of tobacco-related illnesses and fatalities remains too high, however, and new products such as electronic cigarettes raise new questions and challenges.

Prior to the report, there had been evidence for at least a decade of higher incidences of lung cancer among heavy smokers; in 1954 the American Cancer Society announced that smokers had a higher risk of cancer. Three years later, and again in 1959, the U.S. surgeon general, the country's highest ranking government health official, said heavy smoking caused lung cancer.