Cigarette smoking is the number one cause of lung cancer. Scientists have reported widely on the link between cancer and smoking since the 1960s. Since then, study after study has provided more proof that cigarette smoking is the primary cause of lung cancer.  Using tobacco products has been shown to cause cancer. In fact, smoking tobacco, using smokeless tobacco, and being exposed regularly to second-hand tobacco smoke are responsible for a large number of cancer deaths in the U.S. each year.